text: /*
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version 2
   * of the License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
   *
   * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
   * All rights reserved.
   */
  
  /** \file
   * \ingroup edinterface
   */
  
  /* a full doc with API notes can be found in
   * bf-blender/trunk/blender/doc/guides/interface_API.txt */
  
  #include <ctype.h>
  #include <math.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "MEM_guardedalloc.h"
  
  #include "PIL_time.h"
  
  #include "BLI_blenlib.h"
  #include "BLI_math.h"
  #include "BLI_utildefines.h"
  
  #include "BLT_translation.h"
  
  #include "DNA_userdef_types.h"
  
  #include "BKE_context.h"
  #include "BKE_screen.h"
  
  #include "BLF_api.h"
  
  #include "WM_api.h"
  #include "WM_types.h"
  
  #include "ED_screen.h"
  
  #include "UI_interface.h"
  #include "UI_interface_icons.h"
  #include "UI_resources.h"
  #include "UI_view2d.h"
  
  #include "GPU_batch_presets.h"
  #include "GPU_immediate.h"
  #include "GPU_matrix.h"
  #include "GPU_state.h"
  
  #include "interface_intern.h"
  
  /*********************** defines and structs ************************/
  
  #define ANIMATION_TIME 0.30
  #define ANIMATION_INTERVAL 0.02
  
  #define PNL_LAST_ADDED 1
  #define PNL_ACTIVE 2
  #define PNL_WAS_ACTIVE 4
  #define PNL_ANIM_ALIGN 8
  #define PNL_NEW_ADDED 16
  #define PNL_FIRST 32
  
  /* only show pin header button for pinned panels */
  #define USE_PIN_HIDDEN
  
  /* the state of the mouse position relative to the panel */
  typedef enum uiPanelMouseState {
    PANEL_MOUSE_OUTSIDE,        /* mouse is not in the panel */
    PANEL_MOUSE_INSIDE_CONTENT, /* mouse is in the actual panel content */
    PANEL_MOUSE_INSIDE_HEADER,  /* mouse is in the panel header */
    PANEL_MOUSE_INSIDE_SCALE,   /* mouse is inside panel scale widget */
  } uiPanelMouseState;
  
  typedef enum uiHandlePanelState {
    PANEL_STATE_DRAG,
    PANEL_STATE_DRAG_SCALE,
    PANEL_STATE_WAIT_UNTAB,
    PANEL_STATE_ANIMATION,
    PANEL_STATE_EXIT,
  } uiHandlePanelState;
  
  typedef struct uiHandlePanelData {
    uiHandlePanelState state;
  
    /* animation */
    wmTimer *animtimer;
    double starttime;
  
    /* dragging */
    int startx, starty;
    int startofsx, startofsy;
    int startsizex, startsizey;
  } uiHandlePanelData;
  
  static int get_panel_real_size_y(const Panel *panel);
  static void panel_activate_state(const bContext *C, Panel *panel, uiHandlePanelState state);
  
  static void panel_title_color_get(bool show_background, uchar color[4])
  {
    if (show_background) {
      UI_GetThemeColor4ubv(TH_TITLE, color);
    }
    else {
      /* Use menu colors for floating panels. */
      bTheme *btheme = UI_GetTheme();
      const uiWidgetColors *wcol = &btheme->tui.wcol_menu_back;
      copy_v4_v4_uchar(color, (const uchar *)wcol->text);
    }
  }
  
  /*********************** space specific code ************************/
  /* temporary code to remove all sbuts stuff from panel code         */
  
  /* SpaceProperties.align */
  typedef enum eSpaceButtons_Align {
    BUT_HORIZONTAL = 0,
    BUT_VERTICAL = 1,
    BUT_AUTO = 2,
  } eSpaceButtons_Align;
  
  static int panel_aligned(const ScrArea *area, const ARegion *region)
  {
    if (area->spacetype == SPACE_PROPERTIES && region->regiontype == RGN_TYPE_WINDOW) {
      return BUT_VERTICAL;
    }
    else if (area->spacetype == SPACE_USERPREF && region->regiontype == RGN_TYPE_WINDOW) {
      return BUT_VERTICAL;
    }
    else if (area->spacetype == SPACE_FILE && region->regiontype == RGN_TYPE_CHANNELS) {
      return BUT_VERTICAL;
    }
    else if (area->spacetype == SPACE_IMAGE && region->regiontype == RGN_TYPE_PREVIEW) {
      return BUT_VERTICAL;
    }
    else if (ELEM(region->regiontype,
                  RGN_TYPE_UI,
                  RGN_TYPE_TOOLS,
                  RGN_TYPE_TOOL_PROPS,
                  RGN_TYPE_HUD,
                  RGN_TYPE_NAV_BAR,
                  RGN_TYPE_EXECUTE)) {
      return BUT_VERTICAL;
    }
  
    return 0;
  }
  
  static bool panel_active_animation_changed(ListBase *lb, Panel **pa_animation, bool *no_animation)
  {
    LISTBASE_FOREACH (Panel *, panel, lb) {
      /* Detect panel active flag changes. */
      if (!(panel->type && panel->type->parent)) {
        if ((panel->runtime_flag & PNL_WAS_ACTIVE) && !(panel->runtime_flag & PNL_ACTIVE)) {
          return true;
        }
        if (!(panel->runtime_flag & PNL_WAS_ACTIVE) && (panel->runtime_flag & PNL_ACTIVE)) {
          return true;
        }
      }
  
      if ((panel->runtime_flag & PNL_ACTIVE) && !(panel->flag & PNL_CLOSED)) {
        if (panel_active_animation_changed(&panel->children, pa_animation, no_animation)) {
          return true;
        }
      }
  
      /* Detect animation. */
      if (panel->activedata) {
        uiHandlePanelData *data = panel->activedata;
        if (data->state == PANEL_STATE_ANIMATION) {
          *pa_animation = panel;
        }
        else {
          /* Don't animate while handling other interaction. */
          *no_animation = true;
        }
      }
      if ((panel->runtime_flag & PNL_ANIM_ALIGN) && !(*pa_animation)) {
        *pa_animation = panel;
      }
    }
  
    return false;
  }
  
  static bool panels_need_realign(ScrArea *area, ARegion *region, Panel **r_panel_animation)
  {
    *r_panel_animation = NULL;
  
    if (area->spacetype == SPACE_PROPERTIES && region->regiontype == RGN_TYPE_WINDOW) {
      SpaceProperties *sbuts = area->spacedata.first;
  
      if (sbuts->mainbo != sbuts->mainb) {
        return true;
      }
    }
    else if (area->spacetype == SPACE_IMAGE && region->regiontype == RGN_TYPE_PREVIEW) {
      return true;
    }
    else if (area->spacetype == SPACE_FILE && region->regiontype == RGN_TYPE_CHANNELS) {
      return true;
    }
  
    /* Detect if a panel was added or removed. */
    Panel *panel_animation = NULL;
    bool no_animation = false;
    if (panel_active_animation_changed(&region->panels, &panel_animation, &no_animation)) {
      return true;
    }
  
    /* Detect panel marked for animation, if we're not already animating. */
    if (panel_animation) {
      if (!no_animation) {
        *r_panel_animation = panel_animation;
      }
      return true;
    }
  
    return false;
  }
  
  /****************************** panels ******************************/
  
  static void panels_collapse_all(ScrArea *area, ARegion *region, const Panel *from_panel)
  {
    const bool has_category_tabs = UI_panel_category_is_visible(region);
    const char *category = has_category_tabs ? UI_panel_category_active_get(region, false) : NULL;
    const int flag = ((panel_aligned(area, region) == BUT_HORIZONTAL) ? PNL_CLOSEDX : PNL_CLOSEDY);
    const PanelType *from_pt = from_panel->type;
    Panel *panel;
  
    for (panel = region->panels.first; panel; panel = panel->next) {
      PanelType *pt = panel->type;
  
      /* close panels with headers in the same context */
      if (pt && from_pt && !(pt->flag & PNL_NO_HEADER)) {
        if (!pt->context[0] || !from_pt->context[0] || STREQ(pt->context, from_pt->context)) {
          if ((panel->flag & PNL_PIN) || !category || !pt->category[0] ||
              STREQ(pt->category, category)) {
            panel->flag &= ~PNL_CLOSED;
            panel->flag |= flag;
          }
        }
      }
    }
  }
  
  Panel *UI_panel_find_by_type(ListBase *lb, PanelType *pt)
  {
    Panel *panel;
    const char *idname = pt->idname;
  
    for (panel = lb->first; panel; panel = panel->next) {
      if (STREQLEN(panel->panelname, idname, sizeof(panel->panelname))) {
        return panel;
      }
    }
    return NULL;
  }
  
  /**
   * \note \a panel should be return value from #UI_panel_find_by_type and can be NULL.
   */
  Panel *UI_panel_begin(ScrArea *area,
                        ARegion *region,
                        ListBase *lb,
                        uiBlock *block,
                        PanelType *pt,
                        Panel *panel,
                        bool *r_open)
  {
    Panel *panel_last, *panel_next;
    const char *drawname = CTX_IFACE_(pt->translation_context, pt->label);
    const char *idname = pt->idname;
    const bool newpanel = (panel == NULL);
    int align = panel_aligned(area, region);
  
    if (!newpanel) {
      panel->type = pt;
    }
    else {
      /* new panel */
      panel = MEM_callocN(sizeof(Panel), "new panel");
      panel->type = pt;
      BLI_strncpy(panel->panelname, idname, sizeof(panel->panelname));
  
      if (pt->flag & PNL_DEFAULT_CLOSED) {
        if (align == BUT_VERTICAL) {
          panel->flag |= PNL_CLOSEDY;
        }
        else {
          panel->flag |= PNL_CLOSEDX;
        }
      }
  
      panel->ofsx = 0;
      panel->ofsy = 0;
      panel->sizex = 0;
      panel->sizey = 0;
      panel->blocksizex = 0;
      panel->blocksizey = 0;
      panel->runtime_flag |= PNL_NEW_ADDED;
  
      BLI_addtail(lb, panel);
    }
  
    /* Do not allow closed panels without headers! Else user could get "disappeared" UI! */
    if ((pt->flag & PNL_NO_HEADER) && (panel->flag & PNL_CLOSED)) {
      panel->flag &= ~PNL_CLOSED;
      /* Force update of panels' positions! */
      panel->sizex = 0;
      panel->sizey = 0;
      panel->blocksizex = 0;
      panel->blocksizey = 0;
    }
  
    BLI_strncpy(panel->drawname, drawname, sizeof(panel->drawname));
  
    /* if a new panel is added, we insert it right after the panel
     * that was last added. this way new panels are inserted in the
     * right place between versions */
    for (panel_last = lb->first; panel_last; panel_last = panel_last->next) {
      if (panel_last->runtime_flag & PNL_LAST_ADDED) {
        BLI_remlink(lb, panel);
        BLI_insertlinkafter(lb, panel_last, panel);
        break;
      }
    }
  
    if (newpanel) {
      panel->sortorder = (panel_last) ? panel_last->sortorder + 1 : 0;
  
      for (panel_next = lb->first; panel_next; panel_next = panel_next->next) {
        if (panel_next != panel && panel_next->sortorder >= panel->sortorder) {
          panel_next->sortorder++;
        }
      }
    }
  
    if (panel_last) {
      panel_last->runtime_flag &= ~PNL_LAST_ADDED;
    }
  
    /* assign to block */
    block->panel = panel;
    panel->runtime_flag |= PNL_ACTIVE | PNL_LAST_ADDED;
    if (region->alignment == RGN_ALIGN_FLOAT) {
      UI_block_theme_style_set(block, UI_BLOCK_THEME_STYLE_POPUP);
    }
  
    *r_open = false;
  
    if (panel->flag & PNL_CLOSED) {
      return panel;
    }
  
    *r_open = true;
  
    return panel;
  }
  
  static float panel_region_offset_x_get(const ARegion *region, int align)
  {
    if (UI_panel_category_is_visible(region)) {
      if (align == BUT_VERTICAL &&
          (RGN_ALIGN_ENUM_FROM_MASK(region->alignment) != RGN_ALIGN_RIGHT)) {
        return UI_PANEL_CATEGORY_MARGIN_WIDTH;
      }
    }
  
    return 0;
  }
  
  void UI_panel_end(
      const ScrArea *area, const ARegion *region, uiBlock *block, int width, int height, bool open)
  {
    Panel *panel = block->panel;
  
    /* Set panel size excluding children. */
    panel->blocksizex = width;
    panel->blocksizey = height;
  
    /* Compute total panel size including children. */
    LISTBASE_FOREACH (Panel *, pachild, &panel->children) {
      if (pachild->runtime_flag & PNL_ACTIVE) {
        width = max_ii(width, pachild->sizex);
        height += get_panel_real_size_y(pachild);
      }
    }
  
    /* Update total panel size. */
    if (panel->runtime_flag & PNL_NEW_ADDED) {
      panel->runtime_flag &= ~PNL_NEW_ADDED;
      panel->sizex = width;
      panel->sizey = height;
    }
    else {
      int old_sizex = panel->sizex, old_sizey = panel->sizey;
      int old_region_ofsx = panel->runtime.region_ofsx;
  
      /* update width/height if non-zero */
      if (width != 0) {
        panel->sizex = width;
      }
      if (height != 0 || open) {
        panel->sizey = height;
      }
  
      /* check if we need to do an animation */
      if (panel->sizex != old_sizex || panel->sizey != old_sizey) {
        panel->runtime_flag |= PNL_ANIM_ALIGN;
        panel->ofsy += old_sizey - panel->sizey;
      }
  
      int align = panel_aligned(area, region);
      if (old_region_ofsx != panel_region_offset_x_get(region, align)) {
        panel->runtime_flag |= PNL_ANIM_ALIGN;
      }
    }
  }
  
  static void ui_offset_panel_block(uiBlock *block)
  {
    const uiStyle *style = UI_style_get_dpi();
  
    /* compute bounds and offset */
    ui_block_bounds_calc(block);
  
    int ofsy = block->panel->sizey - style->panelspace;
  
    LISTBASE_FOREACH (uiBut *, but, &block->buttons) {
      but->rect.ymin += ofsy;
      but->rect.ymax += ofsy;
    }
  
    block->rect.xmax = block->panel->sizex;
    block->rect.ymax = block->panel->sizey;
    block->rect.xmin = block->rect.ymin = 0.0;
  }
  
  /**************************** drawing *******************************/
  
  /* triangle 'icon' for panel header */
  void UI_draw_icon_tri(float x, float y, char dir, const float color[4])
  {
    float f3 = 0.05 * U.widget_unit;
    float f5 = 0.15 * U.widget_unit;
    float f7 = 0.25 * U.widget_unit;
  
    if (dir == 'h') {
      UI_draw_anti_tria(x - f3, y - f5, x - f3, y + f5, x + f7, y, color);
    }
    else if (dir == 't') {
      UI_draw_anti_tria(x - f5, y - f7, x + f5, y - f7, x, y + f3, color);
    }
    else { /* 'v' = vertical, down */
      UI_draw_anti_tria(x - f5, y + f3, x + f5, y + f3, x, y - f7, color);
    }
  }
  
  static void ui_draw_anti_x(uint pos, float x1, float y1, float x2, float y2)
  {
  
    /* set antialias line */
    GPU_line_smooth(true);
    GPU_blend(true);
  
    GPU_line_width(2.0);
  
    immBegin(GPU_PRIM_LINES, 4);
  
    immVertex2f(pos, x1, y1);
    immVertex2f(pos, x2, y2);
  
    immVertex2f(pos, x1, y2);
    immVertex2f(pos, x2, y1);
  
    immEnd();
  
    GPU_line_smooth(false);
    GPU_blend(false);
  }
  
  /* x 'icon' for panel header */
  static void ui_draw_x_icon(uint pos, float x, float y)
  {
  
    ui_draw_anti_x(pos, x, y, x + 9.375f, y + 9.375f);
  }
  
  #define PNL_ICON UI_UNIT_X /* could be UI_UNIT_Y too */
  
  static void ui_draw_panel_scalewidget(uint pos, const rcti *rect)
  {
    float xmin, xmax, dx;
    float ymin, ymax, dy;
  
    xmin = rect->xmax - PNL_HEADER + 2;
    xmax = rect->xmax - 3;
    ymin = rect->ymin + 3;
    ymax = rect->ymin + PNL_HEADER - 2;
  
    dx = 0.5f * (xmax - xmin);
    dy = 0.5f * (ymax - ymin);
  
    GPU_blend(true);
    immUniformColor4ub(255, 255, 255, 50);
  
    immBegin(GPU_PRIM_LINES, 4);
  
    immVertex2f(pos, xmin, ymin);
    immVertex2f(pos, xmax, ymax);
  
    immVertex2f(pos, xmin + dx, ymin);
    immVertex2f(pos, xmax, ymax - dy);
  
    immEnd();
  
    immUniformColor4ub(0, 0, 0, 50);
  
    immBegin(GPU_PRIM_LINES, 4);
  
    immVertex2f(pos, xmin, ymin + 1);
    immVertex2f(pos, xmax, ymax + 1);
  
    immVertex2f(pos, xmin + dx, ymin + 1);
    immVertex2f(pos, xmax, ymax - dy + 1);
  
    immEnd();
  
    GPU_blend(false);
  }
  
  /* For button layout next to label. */
  void UI_panel_label_offset(uiBlock *block, int *r_x, int *r_y)
  {
    Panel *panel = block->panel;
    const bool is_subpanel = (panel->type && panel->type->parent);
  
    *r_x = UI_UNIT_X * 1.0f;
    *r_y = UI_UNIT_Y * 1.5f;
  
    if (is_subpanel) {
      *r_x += (0.7f * UI_UNIT_X);
    }
  }
  
  static void ui_draw_aligned_panel_header(
      uiStyle *style, uiBlock *block, const rcti *rect, char dir, const bool show_background)
  {
    Panel *panel = block->panel;
    rcti hrect;
    int pnl_icons;
    const char *activename = panel->drawname[0] ? panel->drawname : panel->panelname;
    const bool is_subpanel = (panel->type && panel->type->parent);
    uiFontStyle *fontstyle = (is_subpanel) ? &style->widgetlabel : &style->paneltitle;
    uchar col_title[4];
  
    /* + 0.001f to avoid flirting with float inaccuracy */
    if (panel->control & UI_PNL_CLOSE) {
      pnl_icons = (panel->labelofs + (2.0f * PNL_ICON)) / block->aspect + 0.001f;
    }
    else {
      pnl_icons = (panel->labelofs + (1.1f * PNL_ICON)) / block->aspect + 0.001f;
    }
  
    /* draw text label */
    panel_title_color_get(show_background, col_title);
    col_title[3] = 255;
  
    hrect = *rect;
    if (dir == 'h') {
      hrect.xmin = rect->xmin + pnl_icons;
      hrect.ymin -= 2.0f / block->aspect;
      UI_fontstyle_draw(fontstyle,
                        &hrect,
                        activename,
                        col_title,
                        &(struct uiFontStyleDraw_Params){
                            .align = UI_STYLE_TEXT_LEFT,
                        });
    }
    else {
      /* ignore 'pnl_icons', otherwise the text gets offset horizontally
       * + 0.001f to avoid flirting with float inaccuracy
       */
      hrect.xmin = rect->xmin + (PNL_ICON + 5) / block->aspect + 0.001f;
      UI_fontstyle_draw_rotated(fontstyle, &hrect, activename, col_title);
    }
  }
  
  /* panel integrated in buttonswindow, tool/property lists etc */
  void ui_draw_aligned_panel(uiStyle *style,
                             uiBlock *block,
                             const rcti *rect,
                             const bool show_pin,
                             const bool show_background)
  {
    Panel *panel = block->panel;
    rcti headrect;
    rctf itemrect;
    float color[4];
    const bool is_closed_x = (panel->flag & PNL_CLOSEDX) ? true : false;
    const bool is_closed_y = (panel->flag & PNL_CLOSEDY) ? true : false;
    const bool is_subpanel = (panel->type && panel->type->parent);
    const bool show_drag = (!is_subpanel &&
                            /* FIXME(campbell): currently no background means floating panel which
                             * can't be dragged. This may be changed in future. */
                            show_background);
    const int panel_col = is_subpanel ? TH_PANEL_SUB_BACK : TH_PANEL_BACK;
  
    if (panel->type && (panel->type->flag & PNL_NO_HEADER)) {
      if (show_background) {
        uint pos = GPU_vertformat_attr_add(
            immVertexFormat(), "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
        immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
        immUniformThemeColor(panel_col);
        immRectf(pos, rect->xmin, rect->ymin, rect->xmax, rect->ymax);
        immUnbindProgram();
      }
      return;
    }
  
    /* calculate header rect */
    /* + 0.001f to prevent flicker due to float inaccuracy */
    headrect = *rect;
    headrect.ymin = headrect.ymax;
    headrect.ymax = headrect.ymin + floor(PNL_HEADER / block->aspect + 0.001f);
  
    rcti titlerect = headrect;
    if (is_subpanel) {
      titlerect.xmin += (0.7f * UI_UNIT_X) / block->aspect + 0.001f;
    }
  
    uint pos = GPU_vertformat_attr_add(immVertexFormat(), "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
    immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
  
    if (show_background && !is_subpanel) {
      float minx = rect->xmin;
      float maxx = is_closed_x ? (minx + PNL_HEADER / block->aspect) : rect->xmax;
      float y = headrect.ymax;
  
      GPU_blend(true);
  
      /* draw with background color */
      immUniformThemeColor(TH_PANEL_HEADER);
      immRectf(pos, minx, headrect.ymin, maxx, y);
  
      immBegin(GPU_PRIM_LINES, 4);
  
      immVertex2f(pos, minx, y);
      immVertex2f(pos, maxx, y);
  
      immVertex2f(pos, minx, y);
      immVertex2f(pos, maxx, y);
  
      immEnd();
  
      GPU_blend(false);
    }
  
    immUnbindProgram();
  
    /* draw optional pin icon */
  
  #ifdef USE_PIN_HIDDEN
    if (show_pin && (block->panel->flag & PNL_PIN))
  #else
    if (show_pin)
  #endif
    {
      uchar col_title[4];
      panel_title_color_get(show_background, col_title);
  
      GPU_blend(true);
      UI_icon_draw_ex(headrect.xmax - ((PNL_ICON * 2.2f) / block->aspect),
                      headrect.ymin + (5.0f / block->aspect),
                      (panel->flag & PNL_PIN) ? ICON_PINNED : ICON_UNPINNED,
                      (block->aspect * U.inv_dpi_fac),
                      1.0f,
                      0.0f,
                      col_title,
                      false);
      GPU_blend(false);
    }
  
    /* horizontal title */
    if (is_closed_x == false) {
      ui_draw_aligned_panel_header(style, block, &titlerect, 'h', show_background);
  
      if (show_drag) {
        /* itemrect smaller */
        const float scale = 0.7;
        itemrect.xmax = headrect.xmax - (0.2f * UI_UNIT_X);
        itemrect.xmin = itemrect.xmax - BLI_rcti_size_y(&headrect);
        itemrect.ymin = headrect.ymin;
        itemrect.ymax = headrect.ymax;
        BLI_rctf_scale(&itemrect, scale);
  
        GPU_matrix_push();
        GPU_matrix_translate_2f(itemrect.xmin, itemrect.ymin);
  
        const int col_tint = 84;
        float col_high[4], col_dark[4];
        UI_GetThemeColorShade4fv(TH_PANEL_HEADER, col_tint, col_high);
        UI_GetThemeColorShade4fv(TH_PANEL_BACK, -col_tint, col_dark);
  
        GPUBatch *batch = GPU_batch_preset_panel_drag_widget(
            U.pixelsize, col_high, col_dark, BLI_rcti_size_y(&headrect) * scale);
        GPU_batch_program_set_builtin(batch, GPU_SHADER_2D_FLAT_COLOR);
        GPU_batch_draw(batch);
        GPU_matrix_pop();
      }
    }
  
    /* if the panel is minimized vertically:
     * (------)
     */
    if (is_closed_y) {
      /* skip */
    }
    else if (is_closed_x) {
      /* draw vertical title */
      ui_draw_aligned_panel_header(style, block, &headrect, 'v', show_background);
      pos = GPU_vertformat_attr_add(immVertexFormat(), "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
    }
    /* an open panel */
    else {
      /* in some occasions, draw a border */
      if (panel->flag & PNL_SELECT) {
        if (panel->control & UI_PNL_SOLID) {
          UI_draw_roundbox_corner_set(UI_CNR_ALL);
        }
        else {
          UI_draw_roundbox_corner_set(UI_CNR_NONE);
        }
  
        UI_GetThemeColorShade4fv(TH_BACK, -120, color);
        UI_draw_roundbox_aa(false,
                            0.5f + rect->xmin,
                            0.5f + rect->ymin,
                            0.5f + rect->xmax,
                            0.5f + headrect.ymax + 1,
                            8,
                            color);
      }
  
      immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
  
      GPU_blend(true);
  
      if (show_background) {
        /* panel backdrop */
        immUniformThemeColor(panel_col);
        immRectf(pos, rect->xmin, rect->ymin, rect->xmax, rect->ymax);
      }
  
      if (panel->control & UI_PNL_SCALE) {
        ui_draw_panel_scalewidget(pos, rect);
      }
  
      immUnbindProgram();
    }
  
    uchar col_title[4];
    panel_title_color_get(show_background, col_title);
  
    /* draw optional close icon */
  
    if (panel->control & UI_PNL_CLOSE) {
      const int ofsx = 6;
      immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
      immUniformColor3ubv(col_title);
      ui_draw_x_icon(pos, rect->xmin + 2 + ofsx, rect->ymax + 2);
      immUnbindProgram();
    }
  
    /* draw collapse icon */
  
    /* itemrect smaller */
    itemrect.xmin = titlerect.xmin;
    itemrect.xmax = itemrect.xmin + BLI_rcti_size_y(&titlerect);
    itemrect.ymin = titlerect.ymin;
    itemrect.ymax = titlerect.ymax;
  
    BLI_rctf_scale(&itemrect, 0.25f);
  
    {
      float tria_color[4];
      rgb_uchar_to_float(tria_color, col_title);
      tria_color[3] = 1.0f;
  
      if (is_closed_y) {
        ui_draw_anti_tria_rect(&itemrect, 'h', tria_color);
      }
      else if (is_closed_x) {
        ui_draw_anti_tria_rect(&itemrect, 'h', tria_color);
      }
      else {
        ui_draw_anti_tria_rect(&itemrect, 'v', tria_color);
      }
    }
  }
  
  /************************** panel alignment *************************/
  
  static int get_panel_header(const Panel *panel)
  {
    if (panel->type && (panel->type->flag & PNL_NO_HEADER)) {
      return 0;
    }
  
    return PNL_HEADER;
  }
  
  static int get_panel_size_y(const Panel *panel)
  {
    if (panel->type && (panel->type->flag & PNL_NO_HEADER)) {
      return panel->sizey;
    }
  
    return PNL_HEADER + panel->sizey;
  }
  
  static int get_panel_real_size_y(const Panel *panel)
  {
    int sizey = (panel->flag & PNL_CLOSED) ? 0 : panel->sizey;
  
    if (panel->type && (panel->type->flag & PNL_NO_HEADER)) {
      return sizey;
    }
  
    return PNL_HEADER + sizey;
  }
  
  int UI_panel_size_y(const Panel *panel)
  {
    return get_panel_real_size_y(panel);
  }
  
  /* this function is needed because uiBlock and Panel itself don't
   * change sizey or location when closed */
  static int get_panel_real_ofsy(Panel *panel)
  {
    if (panel->flag & PNL_CLOSEDY) {
      return panel->ofsy + panel->sizey;
    }
    else {
      return panel->ofsy;
    }
  }
  
  static int get_panel_real_ofsx(Panel *panel)
  {
    if (panel->flag & PNL_CLOSEDX) {
      return panel->ofsx + get_panel_header(panel);
    }
    else {
      return panel->ofsx + panel->sizex;
    }
  }
  
  typedef struct PanelSort {
    Panel *panel, *orig;
  } PanelSort;
  
  /**
   * \note about sorting;
   * the sortorder has a lower value for new panels being added.
   * however, that only works to insert a single panel, when more new panels get
   * added the coordinates of existing panels and the previously stored to-be-inserted
   * panels do not match for sorting
   */
  
  static int find_leftmost_panel(const void *a1, const void *a2)
  {
    const PanelSort *ps1 = a1, *ps2 = a2;
  
    if (ps1->panel->ofsx > ps2->panel->ofsx) {
      return 1;
    }
    else if (ps1->panel->ofsx < ps2->panel->ofsx) {
      return -1;
    }
    else if (ps1->panel->sortorder > ps2->panel->sortorder) {
      return 1;
    }
    else if (ps1->panel->sortorder < ps2->panel->sortorder) {
      return -1;
    }
  
    return 0;
  }
  
  static int find_highest_panel(const void *a1, const void *a2)
  {
    const PanelSort *ps1 = a1, *ps2 = a2;
  
    /* stick uppermost header-less panels to the top of the region -
     * prevent them from being sorted (multiple header-less panels have to be sorted though) */
    if (ps1->panel->type->flag & PNL_NO_HEADER && ps2->panel->type->flag & PNL_NO_HEADER) {
      /* skip and check for ofs and sortorder below */
    }
    else if (ps1->panel->type->flag & PNL_NO_HEADER) {
      return -1;
    }
    else if (ps2->panel->type->flag & PNL_NO_HEADER) {
      return 1;
    }
  
    if (ps1->panel->ofsy + ps1->panel->sizey < ps2->panel->ofsy + ps2->panel->sizey) {
      return 1;
    }
    else if (ps1->panel->ofsy + ps1->panel->sizey > ps2->panel->ofsy + ps2->panel->sizey) {
      return -1;
    }
    else if (ps1->panel->sortorder > ps2->panel->sortorder) {
      return 1;
    }
    else if (ps1->panel->sortorder < ps2->panel->sortorder) {
      return -1;
    }
  
    return 0;
  }
  
  static int compare_panel(const void *a1, const void *a2)
  {
    const PanelSort *ps1 = a1, *ps2 = a2;
  
    if (ps1->panel->sortorder > ps2->panel->sortorder) {
      return 1;
    }
    else if (ps1->panel->sortorder < ps2->panel->sortorder) {
      return -1;
    }
  
    return 0;
  }
  
  static void align_sub_panels(Panel *panel)
  {
    /* Position sub panels. */
    int ofsy = panel->ofsy + panel->sizey - panel->blocksizey;
  
    LISTBASE_FOREACH (Panel *, pachild, &panel->children) {
      if (pachild->runtime_flag & PNL_ACTIVE) {
        pachild->ofsx = panel->ofsx;
        pachild->ofsy = ofsy - get_panel_size_y(pachild);
        ofsy -= get_panel_real_size_y(pachild);
  
        if (pachild->children.first) {
          align_sub_panels(pachild);
        }
      }
    }
  }
  
  /* this doesn't draw */
  /* returns 1 when it did something */
  static bool uiAlignPanelStep(ScrArea *area, ARegion *region, const float fac, const bool drag)
  {
    Panel *panel;
    PanelSort *ps, *panelsort, *psnext;
    int a, tot = 0;
    bool done;
    int align = panel_aligned(area, region);
  
    /* count active, not tabbed panels */
    for (panel = region->panels.first; panel; panel = panel->next) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        tot++;
      }
    }
  
    if (tot == 0) {
      return 0;
    }
  
    /* extra; change close direction? */
    for (panel = region->panels.first; panel; panel = panel->next) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        if ((panel->flag & PNL_CLOSEDX) && (align == BUT_VERTICAL)) {
          panel->flag ^= PNL_CLOSED;
        }
        else if ((panel->flag & PNL_CLOSEDY) && (align == BUT_HORIZONTAL)) {
          panel->flag ^= PNL_CLOSED;
        }
      }
    }
  
    /* sort panels */
    panelsort = MEM_callocN(tot * sizeof(PanelSort), "panelsort");
  
    ps = panelsort;
    for (panel = region->panels.first; panel; panel = panel->next) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        ps->panel = MEM_dupallocN(panel);
        ps->orig = panel;
        ps++;
      }
    }
  
    if (drag) {
      /* while we are dragging, we sort on location and update sortorder */
      if (align == BUT_VERTICAL) {
        qsort(panelsort, tot, sizeof(PanelSort), find_highest_panel);
      }
      else {
        qsort(panelsort, tot, sizeof(PanelSort), find_leftmost_panel);
      }
  
      for (ps = panelsort, a = 0; a < tot; a++, ps++) {
        ps->orig->sortorder = a;
      }
    }
    else {
      /* otherwise use sortorder */
      qsort(panelsort, tot, sizeof(PanelSort), compare_panel);
    }
  
    /* no smart other default start loc! this keeps switching f5/f6/etc compatible */
    ps = panelsort;
    ps->panel->runtime.region_ofsx = panel_region_offset_x_get(region, align);
    ps->panel->ofsx = 0;
    ps->panel->ofsy = -get_panel_size_y(ps->panel);
    ps->panel->ofsx += ps->panel->runtime.region_ofsx;
  
    for (a = 0; a < tot - 1; a++, ps++) {
      psnext = ps + 1;
  
      if (align == BUT_VERTICAL) {
        psnext->panel->ofsx = ps->panel->ofsx;
        psnext->panel->ofsy = get_panel_real_ofsy(ps->panel) - get_panel_size_y(psnext->panel);
      }
      else {
        psnext->panel->ofsx = get_panel_real_ofsx(ps->panel);
        psnext->panel->ofsy = ps->panel->ofsy + get_panel_size_y(ps->panel) -
                              get_panel_size_y(psnext->panel);
      }
    }
  
    /* we interpolate */
    done = false;
    ps = panelsort;
    for (a = 0; a < tot; a++, ps++) {
      if ((ps->panel->flag & PNL_SELECT) == 0) {
        if ((ps->orig->ofsx != ps->panel->ofsx) || (ps->orig->ofsy != ps->panel->ofsy)) {
          ps->orig->ofsx = round_fl_to_int(fac * (float)ps->panel->ofsx +
                                           (1.0f - fac) * (float)ps->orig->ofsx);
          ps->orig->ofsy = round_fl_to_int(fac * (float)ps->panel->ofsy +
                                           (1.0f - fac) * (float)ps->orig->ofsy);
          done = true;
        }
      }
    }
  
    /* set locations for tabbed and sub panels */
    for (panel = region->panels.first; panel; panel = panel->next) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        if (panel->children.first) {
          align_sub_panels(panel);
        }
      }
    }
  
    /* free panelsort array */
    for (ps = panelsort, a = 0; a < tot; a++, ps++) {
      MEM_freeN(ps->panel);
    }
    MEM_freeN(panelsort);
  
    return done;
  }
  
  static void ui_panels_size(ScrArea *area, ARegion *region, int *r_x, int *r_y)
  {
    Panel *panel;
    int align = panel_aligned(area, region);
    int sizex = 0;
    int sizey = 0;
  
    /* compute size taken up by panels, for setting in view2d */
    for (panel = region->panels.first; panel; panel = panel->next) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        int pa_sizex, pa_sizey;
  
        if (align == BUT_VERTICAL) {
          pa_sizex = panel->ofsx + panel->sizex;
          pa_sizey = get_panel_real_ofsy(panel);
        }
        else {
          pa_sizex = get_panel_real_ofsx(panel) + panel->sizex;
          pa_sizey = panel->ofsy + get_panel_size_y(panel);
        }
  
        sizex = max_ii(sizex, pa_sizex);
        sizey = min_ii(sizey, pa_sizey);
      }
    }
  
    if (sizex == 0) {
      sizex = UI_PANEL_WIDTH;
    }
    if (sizey == 0) {
      sizey = -UI_PANEL_WIDTH;
    }
  
    *r_x = sizex;
    *r_y = sizey;
  }
  
  static void ui_do_animate(const bContext *C, Panel *panel)
  {
    uiHandlePanelData *data = panel->activedata;
    ScrArea *area = CTX_wm_area(C);
    ARegion *region = CTX_wm_region(C);
    float fac;
  
    fac = (PIL_check_seconds_timer() - data->starttime) / ANIMATION_TIME;
    fac = min_ff(sqrtf(fac), 1.0f);
  
    /* for max 1 second, interpolate positions */
    if (uiAlignPanelStep(area, region, fac, false)) {
      ED_region_tag_redraw(region);
    }
    else {
      fac = 1.0f;
    }
  
    if (fac >= 1.0f) {
      panel_activate_state(C, panel, PANEL_STATE_EXIT);
      return;
    }
  }
  
  static void panel_list_clear_active(ListBase *lb)
  {
    /* set all panels as inactive, so that at the end we know
     * which ones were used */
    LISTBASE_FOREACH (Panel *, panel, lb) {
      if (panel->runtime_flag & PNL_ACTIVE) {
        panel->runtime_flag = PNL_WAS_ACTIVE;
      }
      else {
        panel->runtime_flag = 0;
      }
  
      panel_list_clear_active(&panel->children);
    }
  }
  
  void UI_panels_begin(const bContext *UNUSED(C), ARegion *region)
  {
    panel_list_clear_active(&region->panels);
  }
  
  /* only draws blocks with panels */
  void UI_panels_end(const bContext *C, ARegion *region, int *r_x, int *r_y)
  {
    ScrArea *area = CTX_wm_area(C);
    uiBlock *block;
    Panel *panel, *panel_first;
  
    /* offset contents */
    for (block = region->uiblocks.first; block; block = block->next) {
      if (block->active && block->panel) {
        ui_offset_panel_block(block);
      }
    }
  
    /* re-align, possibly with animation */
    if (panels_need_realign(area, region, &panel)) {
      if (panel) {
        panel_activate_state(C, panel, PANEL_STATE_ANIMATION);
      }
      else {
        uiAlignPanelStep(area, region, 1.0, false);
      }
    }
  
    /* tag first panel */
    panel_first = NULL;
    for (block = region->uiblocks.first; block; block = block->next) {
      if (block->active && block->panel) {
        if (!panel_first || block->panel->sortorder < panel_first->sortorder) {
          panel_first = block->panel;
        }
      }
    }
  
    if (panel_first) {
      panel_first->runtime_flag |= PNL_FIRST;
    }
  
    /* compute size taken up by panel */
    ui_panels_size(area, region, r_x, r_y);
  }
  
  void UI_panels_draw(const bContext *C, ARegion *region)
  {
    uiBlock *block;
  
    if (region->alignment != RGN_ALIGN_FLOAT) {
      UI_ThemeClearColor(TH_BACK);
    }
  
    /* Draw panels, selected on top. Also in reverse order, because
     * UI blocks are added in reverse order and we need child panels
     * to draw on top. */
    for (block = region->uiblocks.last; block; block = block->prev) {
      if (block->active && block->panel && !(block->panel->flag & PNL_SELECT)) {
        UI_block_draw(C, block);
      }
    }
  
    for (block = region->uiblocks.last; block; block = block->prev) {
      if (block->active && block->panel && (block->panel->flag & PNL_SELECT)) {
        UI_block_draw(C, block);
      }
    }
  }
  
  void UI_panels_scale(ARegion *region, float new_width)
  {
    uiBlock *block;
    uiBut *but;
  
    for (block = region->uiblocks.first; block; block = block->next) {
      if (block->panel) {
        float fac = new_width / (float)block->panel->sizex;
        block->panel->sizex = new_width;
  
        for (but = block->buttons.first; but; but = but->next) {
          but->rect.xmin *= fac;
          but->rect.xmax *= fac;
        }
      }
    }
  }
  
  /* ------------ panel merging ---------------- */
  
  static void check_panel_overlap(ARegion *region, Panel *panel)
  {
    Panel *panel_list;
  
    /* also called with (panel == NULL) for clear */
  
    for (panel_list = region->panels.first; panel_list; panel_list = panel_list->next) {
      panel_list->flag &= ~PNL_OVERLAP;
      if (panel && (panel_list != panel)) {
        if (panel_list->runtime_flag & PNL_ACTIVE) {
          float safex = 0.2, safey = 0.2;
  
          if (panel_list->flag & PNL_CLOSEDX) {
            safex = 0.05;
          }
          else if (panel_list->flag & PNL_CLOSEDY) {
            safey = 0.05;
          }
          else if (panel->flag & PNL_CLOSEDX) {
            safex = 0.05;
          }
          else if (panel->flag & PNL_CLOSEDY) {
            safey = 0.05;
          }
  
          if (panel_list->ofsx > panel->ofsx - safex * panel->sizex) {
            if (panel_list->ofsx + panel_list->sizex < panel->ofsx + (1.0f + safex) * panel->sizex) {
              if (panel_list->ofsy > panel->ofsy - safey * panel->sizey) {
                if (panel_list->ofsy + panel_list->sizey <
                    panel->ofsy + (1.0f + safey) * panel->sizey) {
                  panel_list->flag |= PNL_OVERLAP;
                }
              }
            }
          }
        }
      }
    }
  }
  
  /************************ panel dragging ****************************/
  
  static void ui_do_drag(const bContext *C, const wmEvent *event, Panel *panel)
  {
    uiHandlePanelData *data = panel->activedata;
    ScrArea *area = CTX_wm_area(C);
    ARegion *region = CTX_wm_region(C);
    short align = panel_aligned(area, region), dx = 0, dy = 0;
  
    /* first clip for window, no dragging outside */
    if (!BLI_rcti_isect_pt_v(&region->winrct, &event->x)) {
      return;
    }
  
    dx = (event->x - data->startx) & ~(PNL_GRID - 1);
    dy = (event->y - data->starty) & ~(PNL_GRID - 1);
  
    dx *= (float)BLI_rctf_size_x(&region->v2d.cur) / (float)BLI_rcti_size_x(&region->winrct);
    dy *= (float)BLI_rctf_size_y(&region->v2d.cur) / (float)BLI_rcti_size_y(&region->winrct);
  
    if (data->state == PANEL_STATE_DRAG_SCALE) {
      panel->sizex = MAX2(data->startsizex + dx, UI_PANEL_MINX);
  
      if (data->startsizey - dy < UI_PANEL_MINY) {
        dy = -UI_PANEL_MINY + data->startsizey;
      }
  
      panel->sizey = data->startsizey - dy;
      panel->ofsy = data->startofsy + dy;
    }
    else {
      /* reset the panel snapping, to allow dragging away from snapped edges */
      panel->snap = PNL_SNAP_NONE;
  
      panel->ofsx = data->startofsx + dx;
      panel->ofsy = data->startofsy + dy;
      check_panel_overlap(region, panel);
  
      if (align) {
        uiAlignPanelStep(area, region, 0.2, true);
      }
    }
  
    ED_region_tag_redraw(region);
  }
  
  /******************* region level panel interaction *****************/
  
  static uiPanelMouseState ui_panel_mouse_state_get(const uiBlock *block,
                                                    const Panel *panel,
                                                    const int mx,
                                                    const int my)
  {
    /* open panel */
    if (panel->flag & PNL_CLOSEDX) {
      if ((block->rect.xmin <= mx) && (block->rect.xmin + PNL_HEADER >= mx)) {
        return PANEL_MOUSE_INSIDE_HEADER;
      }
    }
    /* outside left/right side */
    else if ((block->rect.xmin > mx) || (block->rect.xmax < mx)) {
      /* pass */
    }
    else if ((block->rect.ymax <= my) && (block->rect.ymax + PNL_HEADER >= my)) {
      return PANEL_MOUSE_INSIDE_HEADER;
    }
    /* open panel */
    else if (!(panel->flag & PNL_CLOSEDY)) {
      if (panel->control & UI_PNL_SCALE) {
        if (block->rect.xmax - PNL_HEADER <= mx) {
          if (block->rect.ymin + PNL_HEADER >= my) {
            return PANEL_MOUSE_INSIDE_SCALE;
          }
        }
      }
      if ((block->rect.xmin <= mx) && (block->rect.xmax >= mx)) {
        if ((block->rect.ymin <= my) && (block->rect.ymax + PNL_HEADER >= my)) {
          return PANEL_MOUSE_INSIDE_CONTENT;
        }
      }
    }
    return PANEL_MOUSE_OUTSIDE;
  }
  
  typedef struct uiPanelDragCollapseHandle {
    bool was_first_open;
    int xy_init[2];
  } uiPanelDragCollapseHandle;
  
  static void ui_panel_drag_collapse_handler_remove(bContext *UNUSED(C), void *userdata)
  {
    uiPanelDragCollapseHandle *dragcol_data = userdata;
    MEM_freeN(dragcol_data);
  }
  
  static void ui_panel_drag_collapse(bContext *C,
                                     uiPanelDragCollapseHandle *dragcol_data,
                                     const int xy_dst[2])
  {
    ScrArea *area = CTX_wm_area(C);
    ARegion *region = CTX_wm_region(C);
    uiBlock *block;
    Panel *panel;
  
    for (block = region->uiblocks.first; block; block = block->next) {
      float xy_a_block[2] = {UNPACK2(dragcol_data->xy_init)};
      float xy_b_block[2] = {UNPACK2(xy_dst)};
      rctf rect = block->rect;
      int oldflag;
      const bool is_horizontal = (panel_aligned(area, region) == BUT_HORIZONTAL);
  
      if ((panel = block->panel) == 0 || (panel->type && (panel->type->flag & PNL_NO_HEADER))) {
        continue;
      }
      oldflag = panel->flag;
  
      /* lock one axis */
      if (is_horizontal) {
        xy_b_block[1] = dragcol_data->xy_init[1];
      }
      else {
        xy_b_block[0] = dragcol_data->xy_init[0];
      }
  
      /* use cursor coords in block space */
      ui_window_to_block_fl(region, block, &xy_a_block[0], &xy_a_block[1]);
      ui_window_to_block_fl(region, block, &xy_b_block[0], &xy_b_block[1]);
  
      /* set up rect to match header size */
      rect.ymin = rect.ymax;
      rect.ymax = rect.ymin + PNL_HEADER;
      if (panel->flag & PNL_CLOSEDX) {
        rect.xmax = rect.xmin + PNL_HEADER;
      }
  
      /* touch all panels between last mouse coord and the current one */
      if (BLI_rctf_isect_segment(&rect, xy_a_block, xy_b_block)) {
        /* force panel to close */
        if (dragcol_data->was_first_open == true) {
          panel->flag |= (is_horizontal ? PNL_CLOSEDX : PNL_CLOSEDY);
        }
        /* force panel to open */
        else {
          panel->flag &= ~PNL_CLOSED;
        }
  
        /* if panel->flag has changed this means a panel was opened/closed here */
        if (panel->flag != oldflag) {
          panel_activate_state(C, panel, PANEL_STATE_ANIMATION);
        }
      }
    }
  }
  
  /**
   * Panel drag-collapse (modal handler)
   * Clicking and dragging over panels toggles their collapse state based on the panel that was first
   * dragged over. If it was open all affected panels incl the initial one are closed and vice versa.
   */
  static int ui_panel_drag_collapse_handler(bContext *C, const wmEvent *event, void *userdata)
  {
    wmWindow *win = CTX_wm_window(C);
    uiPanelDragCollapseHandle *dragcol_data = userdata;
    short retval = WM_UI_HANDLER_CONTINUE;
  
    switch (event->type) {
      case MOUSEMOVE:
        ui_panel_drag_collapse(C, dragcol_data, &event->x);
  
        retval = WM_UI_HANDLER_BREAK;
        break;
      case LEFTMOUSE:
        if (event->val == KM_RELEASE) {
          /* done! */
          WM_event_remove_ui_handler(&win->modalhandlers,
                                     ui_panel_drag_collapse_handler,
                                     ui_panel_drag_collapse_handler_remove,
                                     dragcol_data,
                                     true);
          ui_panel_drag_collapse_handler_remove(C, dragcol_data);
        }
        /* don't let any left-mouse event fall through! */
        retval = WM_UI_HANDLER_BREAK;
        break;
    }
  
    return retval;
  }
  
  static void ui_panel_drag_collapse_handler_add(const bContext *C, const bool was_open)
  {
    wmWindow *win = CTX_wm_window(C);
    const wmEvent *event = win->eventstate;
    uiPanelDragCollapseHandle *dragcol_data = MEM_mallocN(sizeof(*dragcol_data), __func__);
  
    dragcol_data->was_first_open = was_open;
    copy_v2_v2_int(dragcol_data->xy_init, &event->x);
  
    WM_event_add_ui_handler(C,
                            &win->modalhandlers,
                            ui_panel_drag_collapse_handler,
                            ui_panel_drag_collapse_handler_remove,
                            dragcol_data,
                            0);
  }
  
  /* this function is supposed to call general window drawing too */
  /* also it supposes a block has panel, and isn't a menu */
  static void ui_handle_panel_header(
      const bContext *C, uiBlock *block, int mx, int my, int event, short ctrl, short shift)
  {
    ScrArea *area = CTX_wm_area(C);
    ARegion *region = CTX_wm_region(C);
  #ifdef USE_PIN_HIDDEN
    const bool show_pin = UI_panel_category_is_visible(region) &&
                          (block->panel->type->parent == NULL) && (block->panel->flag & PNL_PIN);
  #else
    const bool show_pin = UI_panel_category_is_visible(region) &&
                          (block->panel->type->parent == NULL);
  #endif
    const bool is_subpanel = (block->panel->type && block->panel->type->parent);
    const bool show_drag = !is_subpanel;
  
    int align = panel_aligned(area, region), button = 0;
  
    rctf rect_drag, rect_pin;
    float rect_leftmost;
  
    /* drag and pin rect's */
    rect_drag = block->rect;
    rect_drag.xmin = block->rect.xmax - (PNL_ICON * 1.5f);
    rect_pin = rect_drag;
    if (show_pin) {
      BLI_rctf_translate(&rect_pin, -PNL_ICON, 0.0f);
    }
    rect_leftmost = rect_pin.xmin;
  
    /* mouse coordinates in panel space! */
  
    /* XXX weak code, currently it assumes layout style for location of widgets */
  
    /* check open/collapsed button */
    if (event == EVT_RETKEY) {
      button = 1;
    }
    else if (event == EVT_AKEY) {
      button = 1;
    }
    else if (ELEM(event, 0, EVT_RETKEY, LEFTMOUSE) && shift) {
      if (block->panel->type->parent == NULL) {
        block->panel->flag ^= PNL_PIN;
        button = 2;
      }
    }
    else if (block->panel->flag & PNL_CLOSEDX) {
      if (my >= block->rect.ymax) {
        button = 1;
      }
    }
    else if (block->panel->control & UI_PNL_CLOSE) {
      /* whole of header can be used to collapse panel (except top-right corner) */
      if (mx <= block->rect.xmax - 8 - PNL_ICON) {
        button = 2;
      }
      // else if (mx <= block->rect.xmin + 10 + 2 * PNL_ICON + 2) {
      //  button = 1;
      //}
    }
    else if (mx < rect_leftmost) {
      button = 1;
    }
  
    if (button) {
      if (button == 2) { /* close */
        ED_region_tag_redraw(region);
      }
      else { /* collapse */
        if (ctrl) {
          /* Only collapse all for parent panels. */
          if (block->panel->type != NULL && block->panel->type->parent == NULL) {
            panels_collapse_all(area, region, block->panel);
  
            /* reset the view - we don't want to display a view without content */
            UI_view2d_offset(&region->v2d, 0.0f, 1.0f);
          }
        }
  
        if (block->panel->flag & PNL_CLOSED) {
          block->panel->flag &= ~PNL_CLOSED;
          /* snap back up so full panel aligns with screen edge */
          if (block->panel->snap & PNL_SNAP_BOTTOM) {
            block->panel->ofsy = 0;
          }
  
          if (event == LEFTMOUSE) {
            ui_panel_drag_collapse_handler_add(C, false);
          }
        }
        else if (align == BUT_HORIZONTAL) {
          block->panel->flag |= PNL_CLOSEDX;
  
          if (event == LEFTMOUSE) {
            ui_panel_drag_collapse_handler_add(C, true);
          }
        }
        else {
          /* snap down to bottom screen edge */
          block->panel->flag |= PNL_CLOSEDY;
          if (block->panel->snap & PNL_SNAP_BOTTOM) {
            block->panel->ofsy = -block->panel->sizey;
          }
  
          if (event == LEFTMOUSE) {
            ui_panel_drag_collapse_handler_add(C, true);
          }
        }
      }
  
      if (align) {
        panel_activate_state(C, block->panel, PANEL_STATE_ANIMATION);
      }
      else {
        /* FIXME: this doesn't update the panel drawing, assert to avoid debugging why this is.
         * We could fix this in the future if it's ever needed. */
        BLI_assert(0);
        ED_region_tag_redraw(region);
      }
    }
    else if (show_drag && BLI_rctf_isect_x(&rect_drag, mx)) {
      /* XXX, for now don't allow dragging in floating windows yet. */
      if (region->alignment == RGN_ALIGN_FLOAT) {
        return;
      }
      panel_activate_state(C, block->panel, PANEL_STATE_DRAG);
    }
    else if (show_pin && BLI_rctf_isect_x(&rect_pin, mx)) {
      block->panel->flag ^= PNL_PIN;
      ED_region_tag_redraw(region);
    }
  }
  
  bool UI_panel_category_is_visible(const ARegion *region)
  {
    /* more than one */
    return region->panels_category.first &&
           region->panels_category.first != region->panels_category.last;
  }
  
  PanelCategoryDyn *UI_panel_category_find(ARegion *region, const char *idname)
  {
    return BLI_findstring(&region->panels_category, idname, offsetof(PanelCategoryDyn, idname));
  }
  
  PanelCategoryStack *UI_panel_category_active_find(ARegion *region, const char *idname)
  {
    return BLI_findstring(
        &region->panels_category_active, idname, offsetof(PanelCategoryStack, idname));
  }
  
  static void ui_panel_category_active_set(ARegion *region, const char *idname, bool fallback)
  {
    ListBase *lb = &region->panels_category_active;
    PanelCategoryStack *pc_act = UI_panel_category_active_find(region, idname);
  
    if (pc_act) {
      BLI_remlink(lb, pc_act);
    }
    else {
      pc_act = MEM_callocN(sizeof(PanelCategoryStack), __func__);
      BLI_strncpy(pc_act->idname, idname, sizeof(pc_act->idname));
    }
  
    if (fallback) {
      /* For fallbacks, add at the end so explicitly chosen categories have priority. */
      BLI_addtail(lb, pc_act);
    }
    else {
      BLI_addhead(lb, pc_act);
    }
  
    /* validate all active panels, we could do this on load,
     * they are harmless - but we should remove somewhere.
     * (addons could define own and gather cruft over time) */
    {
      PanelCategoryStack *pc_act_next;
      /* intentionally skip first */
      pc_act_next = pc_act->next;
      while ((pc_act = pc_act_next)) {
        pc_act_next = pc_act->next;
        if (!BLI_findstring(
                &region->type->paneltypes, pc_act->idname, offsetof(PanelType, category))) {
          BLI_remlink(lb, pc_act);
          MEM_freeN(pc_act);
        }
      }
    }
  }
  
  void UI_panel_category_active_set(ARegion *region, const char *idname)
  {
    ui_panel_category_active_set(region, idname, false);
  }
  
  void UI_panel_category_active_set_default(ARegion *region, const char *idname)
  {
    if (!UI_panel_category_active_find(region, idname)) {
      ui_panel_category_active_set(region, idname, true);
    }
  }
  
  const char *UI_panel_category_active_get(ARegion *region, bool set_fallback)
  {
    PanelCategoryStack *pc_act;
  
    for (pc_act = region->panels_category_active.first; pc_act; pc_act = pc_act->next) {
      if (UI_panel_category_find(region, pc_act->idname)) {
        return pc_act->idname;
      }
    }
  
    if (set_fallback) {
      PanelCategoryDyn *pc_dyn = region->panels_category.first;
      if (pc_dyn) {
        ui_panel_category_active_set(region, pc_dyn->idname, true);
        return pc_dyn->idname;
      }
    }
  
    return NULL;
  }
  
  PanelCategoryDyn *UI_panel_category_find_mouse_over_ex(ARegion *region, const int x, const int y)
  {
    PanelCategoryDyn *ptd;
  
    for (ptd = region->panels_category.first; ptd; ptd = ptd->next) {
      if (BLI_rcti_isect_pt(&ptd->rect, x, y)) {
        return ptd;
      }
    }
  
    return NULL;
  }
  
  PanelCategoryDyn *UI_panel_category_find_mouse_over(ARegion *region, const wmEvent *event)
  {
    return UI_panel_category_find_mouse_over_ex(region, event->mval[0], event->mval[1]);
  }
  
  void UI_panel_category_add(ARegion *region, const char *name)
  {
    PanelCategoryDyn *pc_dyn = MEM_callocN(sizeof(*pc_dyn), __func__);
    BLI_addtail(&region->panels_category, pc_dyn);
  
    BLI_strncpy(pc_dyn->idname, name, sizeof(pc_dyn->idname));
  
    /* 'pc_dyn->rect' must be set on draw */
  }
  
  void UI_panel_category_clear_all(ARegion *region)
  {
    BLI_freelistN(&region->panels_category);
  }
  
  static void imm_buf_append(
      float vbuf[][2], uchar cbuf[][3], float x, float y, const uchar col[3], int *index)
  {
    ARRAY_SET_ITEMS(vbuf[*index], x, y);
    ARRAY_SET_ITEMS(cbuf[*index], UNPACK3(col));
    (*index)++;
  }
  
  /* based on UI_draw_roundbox, check on making a version which allows us to skip some sides */
  static void ui_panel_category_draw_tab(bool filled,
                                         float minx,
                                         float miny,
                                         float maxx,
                                         float maxy,
                                         float rad,
                                         const int roundboxtype,
                                         const bool use_highlight,
                                         const bool use_shadow,
                                         const bool use_flip_x,
                                         const uchar highlight_fade[3],
                                         const uchar col[3])
  {
    float vec[4][2] = {{0.195, 0.02}, {0.55, 0.169}, {0.831, 0.45}, {0.98, 0.805}};
    int a;
  
    /* mult */
    for (a = 0; a < 4; a++) {
      mul_v2_fl(vec[a], rad);
    }
  
    uint vert_len = 0;
    if (use_highlight) {
      vert_len += (roundboxtype & UI_CNR_TOP_RIGHT) ? 6 : 1;
      vert_len += (roundboxtype & UI_CNR_TOP_LEFT) ? 6 : 1;
    }
    if (use_highlight && !use_shadow) {
      vert_len++;
    }
    else {
      vert_len += (roundboxtype & UI_CNR_BOTTOM_RIGHT) ? 6 : 1;
      vert_len += (roundboxtype & UI_CNR_BOTTOM_LEFT) ? 6 : 1;
    }
    /* Maximum size. */
    float vbuf[24][2];
    uchar cbuf[24][3];
    int buf_index = 0;
  
    /* start with corner right-top */
    if (use_highlight) {
      if (roundboxtype & UI_CNR_TOP_RIGHT) {
        imm_buf_append(vbuf, cbuf, maxx, maxy - rad, col, &buf_index);
        for (a = 0; a < 4; a++) {
          imm_buf_append(vbuf, cbuf, maxx - vec[a][1], maxy - rad + vec[a][0], col, &buf_index);
        }
        imm_buf_append(vbuf, cbuf, maxx - rad, maxy, col, &buf_index);
      }
      else {
        imm_buf_append(vbuf, cbuf, maxx, maxy, col, &buf_index);
      }
  
      /* corner left-top */
      if (roundboxtype & UI_CNR_TOP_LEFT) {
        imm_buf_append(vbuf, cbuf, minx + rad, maxy, col, &buf_index);
        for (a = 0; a < 4; a++) {
          imm_buf_append(vbuf, cbuf, minx + rad - vec[a][0], maxy - vec[a][1], col, &buf_index);
        }
        imm_buf_append(vbuf, cbuf, minx, maxy - rad, col, &buf_index);
      }
      else {
        imm_buf_append(vbuf, cbuf, minx, maxy, col, &buf_index);
      }
    }
  
    if (use_highlight && !use_shadow) {
      imm_buf_append(
          vbuf, cbuf, minx, miny + rad, highlight_fade ? col : highlight_fade, &buf_index);
    }
    else {
      /* corner left-bottom */
      if (roundboxtype & UI_CNR_BOTTOM_LEFT) {
        imm_buf_append(vbuf, cbuf, minx, miny + rad, col, &buf_index);
        for (a = 0; a < 4; a++) {
          imm_buf_append(vbuf, cbuf, minx + vec[a][1], miny + rad - vec[a][0], col, &buf_index);
        }
        imm_buf_append(vbuf, cbuf, minx + rad, miny, col, &buf_index);
      }
      else {
        imm_buf_append(vbuf, cbuf, minx, miny, col, &buf_index);
      }
  
      /* corner right-bottom */
      if (roundboxtype & UI_CNR_BOTTOM_RIGHT) {
        imm_buf_append(vbuf, cbuf, maxx - rad, miny, col, &buf_index);
        for (a = 0; a < 4; a++) {
          imm_buf_append(vbuf, cbuf, maxx - rad + vec[a][0], miny + vec[a][1], col, &buf_index);
        }
        imm_buf_append(vbuf, cbuf, maxx, miny + rad, col, &buf_index);
      }
      else {
        imm_buf_append(vbuf, cbuf, maxx, miny, col, &buf_index);
      }
    }
  
    if (use_flip_x) {
      float midx = (minx + maxx) / 2.0f;
      for (int i = 0; i < buf_index; i++) {
        vbuf[i][0] = midx - (vbuf[i][0] - midx);
      }
    }
  
    GPUVertFormat *format = immVertexFormat();
    uint pos = GPU_vertformat_attr_add(format, "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
    uint color = GPU_vertformat_attr_add(
        format, "color", GPU_COMP_U8, 3, GPU_FETCH_INT_TO_FLOAT_UNIT);
  
    immBindBuiltinProgram(GPU_SHADER_2D_SMOOTH_COLOR);
    immBegin(filled ? GPU_PRIM_TRI_FAN : GPU_PRIM_LINE_STRIP, vert_len);
    for (int i = 0; i < buf_index; i++) {
      immAttr3ubv(color, cbuf[i]);
      immVertex2fv(pos, vbuf[i]);
    }
    immEnd();
    immUnbindProgram();
  }
  
  /**
   * Draw vertical tabs on the left side of the region,
   * one tab per category.
   */
  void UI_panel_category_draw_all(ARegion *region, const char *category_id_active)
  {
    /* no tab outlines for */
    // #define USE_FLAT_INACTIVE
    const bool is_left = RGN_ALIGN_ENUM_FROM_MASK(region->alignment != RGN_ALIGN_RIGHT);
    View2D *v2d = &region->v2d;
    const uiStyle *style = UI_style_get();
    const uiFontStyle *fstyle = &style->widget;
    const int fontid = fstyle->uifont_id;
    short fstyle_points = fstyle->points;
    PanelCategoryDyn *pc_dyn;
    const float aspect = ((uiBlock *)region->uiblocks.first)->aspect;
    const float zoom = 1.0f / aspect;
    const int px = max_ii(1, round_fl_to_int(U.pixelsize));
    const int px_x_sign = is_left ? px : -px;
    const int category_tabs_width = round_fl_to_int(UI_PANEL_CATEGORY_MARGIN_WIDTH * zoom);
    const float dpi_fac = UI_DPI_FAC;
    /* padding of tabs around text */
    const int tab_v_pad_text = round_fl_to_int((2 + ((px * 3) * dpi_fac)) * zoom);
    /* padding between tabs */
    const int tab_v_pad = round_fl_to_int((4 + (2 * px * dpi_fac)) * zoom);
    const float tab_curve_radius = ((px * 3) * dpi_fac) * zoom;
    /* We flip the tab drawing, so always use these flags. */
    const int roundboxtype = UI_CNR_TOP_LEFT | UI_CNR_BOTTOM_LEFT;
    bool is_alpha;
    bool do_scaletabs = false;
  #ifdef USE_FLAT_INACTIVE
    bool is_active_prev = false;
  #endif
    float scaletabs = 1.0f;
    /* same for all tabs */
    /* intentionally dont scale by 'px' */
    const int rct_xmin = is_left ? v2d->mask.xmin + 3 : (v2d->mask.xmax - category_tabs_width);
    const int rct_xmax = is_left ? v2d->mask.xmin + category_tabs_width : (v2d->mask.xmax - 3);
    const int text_v_ofs = (rct_xmax - rct_xmin) * 0.3f;
  
    int y_ofs = tab_v_pad;
  
    /* Primary theme colors */
    uchar theme_col_back[4];
    uchar theme_col_text[3];
    uchar theme_col_text_hi[3];
  
    /* Tab colors */
    uchar theme_col_tab_bg[4];
    uchar theme_col_tab_active[3];
    uchar theme_col_tab_inactive[3];
  
    /* Secondary theme colors */
    uchar theme_col_tab_outline[3];
    uchar theme_col_tab_divider[3]; /* line that divides tabs from the main region */
    uchar theme_col_tab_highlight[3];
    uchar theme_col_tab_highlight_inactive[3];
  
    UI_GetThemeColor4ubv(TH_BACK, theme_col_back);
    UI_GetThemeColor3ubv(TH_TEXT, theme_col_text);
    UI_GetThemeColor3ubv(TH_TEXT_HI, theme_col_text_hi);
  
    UI_GetThemeColor4ubv(TH_TAB_BACK, theme_col_tab_bg);
    UI_GetThemeColor3ubv(TH_TAB_ACTIVE, theme_col_tab_active);
    UI_GetThemeColor3ubv(TH_TAB_INACTIVE, theme_col_tab_inactive);
    UI_GetThemeColor3ubv(TH_TAB_OUTLINE, theme_col_tab_outline);
  
    interp_v3_v3v3_uchar(theme_col_tab_divider, theme_col_back, theme_col_tab_outline, 0.3f);
    interp_v3_v3v3_uchar(theme_col_tab_highlight, theme_col_back, theme_col_text_hi, 0.2f);
    interp_v3_v3v3_uchar(
        theme_col_tab_highlight_inactive, theme_col_tab_inactive, theme_col_text_hi, 0.12f);
  
    is_alpha = (region->overlap && (theme_col_back[3] != 255));
  
    if (fstyle->kerning == 1) {
      BLF_enable(fstyle->uifont_id, BLF_KERNING_DEFAULT);
    }
  
    BLF_enable(fontid, BLF_ROTATION);
    BLF_rotation(fontid, M_PI_2);
    // UI_fontstyle_set(&style->widget);
    ui_fontscale(&fstyle_points, aspect / (U.pixelsize * 1.1f));
    BLF_size(fontid, fstyle_points, U.dpi);
  
    /* Check the region type supports categories to avoid an assert
     * for showing 3D view panels in the properties space. */
    if ((1 << region->regiontype) & RGN_TYPE_HAS_CATEGORY_MASK) {
      BLI_assert(UI_panel_category_is_visible(region));
    }
  
    /* calculate tab rect's and check if we need to scale down */
    for (pc_dyn = region->panels_category.first; pc_dyn; pc_dyn = pc_dyn->next) {
      rcti *rct = &pc_dyn->rect;
      const char *category_id = pc_dyn->idname;
      const char *category_id_draw = IFACE_(category_id);
      const int category_width = BLF_width(fontid, category_id_draw, BLF_DRAW_STR_DUMMY_MAX);
  
      rct->xmin = rct_xmin;
      rct->xmax = rct_xmax;
  
      rct->ymin = v2d->mask.ymax - (y_ofs + category_width + (tab_v_pad_text * 2));
      rct->ymax = v2d->mask.ymax - (y_ofs);
  
      y_ofs += category_width + tab_v_pad + (tab_v_pad_text * 2);
    }
  
    if (y_ofs > BLI_rcti_size_y(&v2d->mask)) {
      scaletabs = (float)BLI_rcti_size_y(&v2d->mask) / (float)y_ofs;
  
      for (pc_dyn = region->panels_category.first; pc_dyn; pc_dyn = pc_dyn->next) {
        rcti *rct = &pc_dyn->rect;
        rct->ymin = ((rct->ymin - v2d->mask.ymax) * scaletabs) + v2d->mask.ymax;
        rct->ymax = ((rct->ymax - v2d->mask.ymax) * scaletabs) + v2d->mask.ymax;
      }
  
      do_scaletabs = true;
    }
  
    /* begin drawing */
    GPU_line_smooth(true);
  
    uint pos = GPU_vertformat_attr_add(
        immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
    immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
  
    /* draw the background */
    if (is_alpha) {
      GPU_blend(true);
      immUniformColor4ubv(theme_col_tab_bg);
    }
    else {
      immUniformColor3ubv(theme_col_tab_bg);
    }
  
    if (is_left) {
      immRecti(
          pos, v2d->mask.xmin, v2d->mask.ymin, v2d->mask.xmin + category_tabs_width, v2d->mask.ymax);
    }
    else {
      immRecti(
          pos, v2d->mask.xmax - category_tabs_width, v2d->mask.ymin, v2d->mask.xmax, v2d->mask.ymax);
    }
  
    if (is_alpha) {
      GPU_blend(false);
    }
  
    immUnbindProgram();
  
    const int divider_xmin = is_left ? (v2d->mask.xmin + (category_tabs_width - px)) :
                                       (v2d->mask.xmax - category_tabs_width) + px;
    const int divider_xmax = is_left ? (v2d->mask.xmin + category_tabs_width) :
                                       (v2d->mask.xmax - (category_tabs_width + px)) + px;
  
    for (pc_dyn = region->panels_category.first; pc_dyn; pc_dyn = pc_dyn->next) {
      const rcti *rct = &pc_dyn->rect;
      const char *category_id = pc_dyn->idname;
      const char *category_id_draw = IFACE_(category_id);
      int category_width = BLI_rcti_size_y(rct) - (tab_v_pad_text * 2);
      size_t category_draw_len = BLF_DRAW_STR_DUMMY_MAX;
      // int category_width = BLF_width(fontid, category_id_draw, BLF_DRAW_STR_DUMMY_MAX);
  
      const bool is_active = STREQ(category_id, category_id_active);
  
      GPU_blend(true);
  
  #ifdef USE_FLAT_INACTIVE
      if (is_active)
  #endif
      {
        const bool use_flip_x = !is_left;
        ui_panel_category_draw_tab(true,
                                   rct->xmin,
                                   rct->ymin,
                                   rct->xmax,
                                   rct->ymax,
                                   tab_curve_radius - px,
                                   roundboxtype,
                                   true,
                                   true,
                                   use_flip_x,
                                   NULL,
                                   is_active ? theme_col_tab_active : theme_col_tab_inactive);
  
        /* tab outline */
        ui_panel_category_draw_tab(false,
                                   rct->xmin - px_x_sign,
                                   rct->ymin - px,
                                   rct->xmax - px_x_sign,
                                   rct->ymax + px,
                                   tab_curve_radius,
                                   roundboxtype,
                                   true,
                                   true,
                                   use_flip_x,
                                   NULL,
                                   theme_col_tab_outline);
  
        /* tab highlight (3d look) */
        ui_panel_category_draw_tab(false,
                                   rct->xmin,
                                   rct->ymin,
                                   rct->xmax,
                                   rct->ymax,
                                   tab_curve_radius,
                                   roundboxtype,
                                   true,
                                   false,
                                   use_flip_x,
                                   is_active ? theme_col_back : theme_col_tab_inactive,
                                   is_active ? theme_col_tab_highlight :
                                               theme_col_tab_highlight_inactive);
      }
  
      /* tab blackline */
      if (!is_active) {
        pos = GPU_vertformat_attr_add(
            immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
        immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
  
        immUniformColor3ubv(theme_col_tab_divider);
        immRecti(pos, divider_xmin, rct->ymin - tab_v_pad, divider_xmax, rct->ymax + tab_v_pad);
        immUnbindProgram();
      }
  
      if (do_scaletabs) {
        category_draw_len = BLF_width_to_strlen(
            fontid, category_id_draw, category_draw_len, category_width, NULL);
      }
  
      BLF_position(fontid, rct->xmax - text_v_ofs, rct->ymin + tab_v_pad_text, 0.0f);
  
      /* tab titles */
  
      /* draw white shadow to give text more depth */
      BLF_color3ubv(fontid, theme_col_text);
  
      /* main tab title */
      BLF_draw(fontid, category_id_draw, category_draw_len);
  
      GPU_blend(false);
  
      /* tab blackline remaining (last tab) */
      pos = GPU_vertformat_attr_add(
          immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
      immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
      if (pc_dyn->prev == NULL) {
        immUniformColor3ubv(theme_col_tab_divider);
        immRecti(pos, divider_xmin, rct->ymax + px, divider_xmax, v2d->mask.ymax);
      }
      if (pc_dyn->next == NULL) {
        immUniformColor3ubv(theme_col_tab_divider);
        immRecti(pos, divider_xmin, 0, divider_xmax, rct->ymin);
      }
  
  #ifdef USE_FLAT_INACTIVE
      /* draw line between inactive tabs */
      if (is_active == false && is_active_prev == false && pc_dyn->prev) {
        immUniformColor3ubv(theme_col_tab_divider);
        immRecti(pos,
                 v2d->mask.xmin + (category_tabs_width / 5),
                 rct->ymax + px,
                 (v2d->mask.xmin + category_tabs_width) - (category_tabs_width / 5),
                 rct->ymax + (px * 3));
      }
  
      is_active_prev = is_active;
  #endif
      immUnbindProgram();
  
      /* not essential, but allows events to be handled right up until the region edge [#38171] */
      if (is_left) {
        pc_dyn->rect.xmin = v2d->mask.xmin;
      }
      else {
        pc_dyn->rect.xmax = v2d->mask.xmax;
      }
    }
  
    GPU_line_smooth(false);
  
    BLF_disable(fontid, BLF_ROTATION);
  
    if (fstyle->kerning == 1) {
      BLF_disable(fstyle->uifont_id, BLF_KERNING_DEFAULT);
    }
  
  #undef USE_FLAT_INACTIVE
  }
  
  static int ui_handle_panel_category_cycling(const wmEvent *event,
                                              ARegion *region,
                                              const uiBut *active_but)
  {
    const bool is_mousewheel = ELEM(event->type, WHEELUPMOUSE, WHEELDOWNMOUSE);
    const bool inside_tabregion =
        ((RGN_ALIGN_ENUM_FROM_MASK(region->alignment) != RGN_ALIGN_RIGHT) ?
             (event->mval[0] < ((PanelCategoryDyn *)region->panels_category.first)->rect.xmax) :
             (event->mval[0] > ((PanelCategoryDyn *)region->panels_category.first)->rect.xmin));
  
    /* if mouse is inside non-tab region, ctrl key is required */
    if (is_mousewheel && !event->ctrl && !inside_tabregion) {
      return WM_UI_HANDLER_CONTINUE;
    }
  
    if (active_but && ui_but_supports_cycling(active_but)) {
      /* skip - exception to make cycling buttons
       * using ctrl+mousewheel work in tabbed regions */
    }
    else {
      const char *category = UI_panel_category_active_get(region, false);
      if (LIKELY(category)) {
        PanelCategoryDyn *pc_dyn = UI_panel_category_find(region, category);
        if (LIKELY(pc_dyn)) {
          if (is_mousewheel) {
            /* we can probably get rid of this and only allow ctrl+tabbing */
            pc_dyn = (event->type == WHEELDOWNMOUSE) ? pc_dyn->next : pc_dyn->prev;
          }
          else {
            const bool backwards = event->shift;
            pc_dyn = backwards ? pc_dyn->prev : pc_dyn->next;
            if (!pc_dyn) {
              /* proper cyclic behavior,
               * back to first/last category (only used for ctrl+tab) */
              pc_dyn = backwards ? region->panels_category.last : region->panels_category.first;
            }
          }
  
          if (pc_dyn) {
            /* intentionally don't reset scroll in this case,
             * this allows for quick browsing between tabs */
            UI_panel_category_active_set(region, pc_dyn->idname);
            ED_region_tag_redraw(region);
          }
        }
      }
      return WM_UI_HANDLER_BREAK;
    }
  
    return WM_UI_HANDLER_CONTINUE;
  }
  
  /* XXX should become modal keymap */
  /* AKey is opening/closing panels, independent of button state now */
  
  int ui_handler_panel_region(bContext *C,
                              const wmEvent *event,
                              ARegion *region,
                              const uiBut *active_but)
  {
    uiBlock *block;
    Panel *panel;
    int retval, mx, my;
    bool has_category_tabs = UI_panel_category_is_visible(region);
  
    retval = WM_UI_HANDLER_CONTINUE;
  
    /* Scrollbars can overlap panels now, they have handling priority. */
    if (UI_view2d_mouse_in_scrollers(region, &region->v2d, event->x, event->y)) {
      return retval;
    }
  
    /* handle category tabs */
    if (has_category_tabs) {
      if (event->val == KM_PRESS) {
        if (event->type == LEFTMOUSE) {
          PanelCategoryDyn *pc_dyn = UI_panel_category_find_mouse_over(region, event);
          if (pc_dyn) {
            UI_panel_category_active_set(region, pc_dyn->idname);
            ED_region_tag_redraw(region);
  
            /* reset scroll to the top [#38348] */
            UI_view2d_offset(&region->v2d, -1.0f, 1.0f);
  
            retval = WM_UI_HANDLER_BREAK;
          }
        }
        else if ((event->type == EVT_TABKEY && event->ctrl) ||
                 ELEM(event->type, WHEELUPMOUSE, WHEELDOWNMOUSE)) {
          /* cycle tabs */
          retval = ui_handle_panel_category_cycling(event, region, active_but);
        }
      }
    }
  
    if (retval == WM_UI_HANDLER_BREAK) {
      return retval;
    }
  
    for (block = region->uiblocks.last; block; block = block->prev) {
      uiPanelMouseState mouse_state;
  
      mx = event->x;
      my = event->y;
      ui_window_to_block(region, block, &mx, &my);
  
      /* checks for mouse position inside */
      panel = block->panel;
  
      if (!panel) {
        continue;
      }
      /* XXX - accessed freed panels when scripts reload, need to fix. */
      if (panel->type && panel->type->flag & PNL_NO_HEADER) {
        continue;
      }
  
      mouse_state = ui_panel_mouse_state_get(block, panel, mx, my);
  
      /* XXX hardcoded key warning */
      if (ELEM(mouse_state, PANEL_MOUSE_INSIDE_CONTENT, PANEL_MOUSE_INSIDE_HEADER) &&
          event->val == KM_PRESS) {
        if (event->type == EVT_AKEY &&
            ((event->ctrl + event->oskey + event->shift + event->alt) == 0)) {
  
          if (panel->flag & PNL_CLOSEDY) {
            if ((block->rect.ymax <= my) && (block->rect.ymax + PNL_HEADER >= my)) {
              ui_handle_panel_header(C, block, mx, my, event->type, event->ctrl, event->shift);
            }
          }
          else {
            ui_handle_panel_header(C, block, mx, my, event->type, event->ctrl, event->shift);
          }
  
          retval = WM_UI_HANDLER_BREAK;
          continue;
        }
      }
  
      /* on active button, do not handle panels */
      if (ui_region_find_active_but(region) != NULL) {
        continue;
      }
  
      if (ELEM(mouse_state, PANEL_MOUSE_INSIDE_CONTENT, PANEL_MOUSE_INSIDE_HEADER)) {
  
        if (event->val == KM_PRESS) {
  
          /* open close on header */
          if (ELEM(event->type, EVT_RETKEY, EVT_PADENTER)) {
            if (mouse_state == PANEL_MOUSE_INSIDE_HEADER) {
              ui_handle_panel_header(C, block, mx, my, EVT_RETKEY, event->ctrl, event->shift);
              retval = WM_UI_HANDLER_BREAK;
              break;
            }
          }
          else if (event->type == LEFTMOUSE) {
            /* all inside clicks should return in break - overlapping/float panels */
            retval = WM_UI_HANDLER_BREAK;
  
            if (mouse_state == PANEL_MOUSE_INSIDE_HEADER) {
              ui_handle_panel_header(C, block, mx, my, event->type, event->ctrl, event->shift);
              retval = WM_UI_HANDLER_BREAK;
              break;
            }
            else if ((mouse_state == PANEL_MOUSE_INSIDE_SCALE) && !(panel->flag & PNL_CLOSED)) {
              panel_activate_state(C, panel, PANEL_STATE_DRAG_SCALE);
              retval = WM_UI_HANDLER_BREAK;
              break;
            }
          }
          else if (event->type == RIGHTMOUSE) {
            if (mouse_state == PANEL_MOUSE_INSIDE_HEADER) {
              ui_popup_context_menu_for_panel(C, region, block->panel);
              retval = WM_UI_HANDLER_BREAK;
              break;
            }
          }
          else if (event->type == EVT_ESCKEY) {
            /*XXX 2.50*/
  #if 0
            if (block->handler) {
              rem_blockhandler(area, block->handler);
              ED_region_tag_redraw(region);
              retval = WM_UI_HANDLER_BREAK;
            }
  #endif
          }
          else if (event->type == EVT_PADPLUSKEY || event->type == EVT_PADMINUS) {
  #if 0 /* XXX make float panel exception? */
            int zoom = 0;
  
            /* if panel is closed, only zoom if mouse is over the header */
            if (panel->flag & (PNL_CLOSEDX | PNL_CLOSEDY)) {
              if (inside_header) {
                zoom = 1;
              }
            }
            else {
              zoom = 1;
            }
  
            if (zoom) {
              ScrArea *area = CTX_wm_area(C);
              SpaceLink *sl = area->spacedata.first;
  
              if (area->spacetype != SPACE_PROPERTIES) {
                if (!(panel->control & UI_PNL_SCALE)) {
                  if (event->type == PADPLUSKEY) {
                    sl->blockscale += 0.1;
                  }
                  else {
                    sl->blockscale -= 0.1;
                  }
                  CLAMP(sl->blockscale, 0.6, 1.0);
  
                  ED_region_tag_redraw(region);
                  retval = WM_UI_HANDLER_BREAK;
                }
              }
            }
  #endif
          }
        }
      }
    }
  
    return retval;
  }
  
  /**************** window level modal panel interaction **************/
  
  /* note, this is modal handler and should not swallow events for animation */
  static int ui_handler_panel(bContext *C, const wmEvent *event, void *userdata)
  {
    Panel *panel = userdata;
    uiHandlePanelData *data = panel->activedata;
  
    /* verify if we can stop */
    if (event->type == LEFTMOUSE && event->val == KM_RELEASE) {
      ScrArea *area = CTX_wm_area(C);
      ARegion *region = CTX_wm_region(C);
      int align = panel_aligned(area, region);
  
      if (align) {
        panel_activate_state(C, panel, PANEL_STATE_ANIMATION);
      }
      else {
        panel_activate_state(C, panel, PANEL_STATE_EXIT);
      }
    }
    else if (event->type == MOUSEMOVE) {
      if (data->state == PANEL_STATE_DRAG) {
        ui_do_drag(C, event, panel);
      }
    }
    else if (event->type == TIMER && event->customdata == data->animtimer) {
      if (data->state == PANEL_STATE_ANIMATION) {
        ui_do_animate(C, panel);
      }
      else if (data->state == PANEL_STATE_DRAG) {
        ui_do_drag(C, event, panel);
      }
    }
  
    data = panel->activedata;
  
    if (data && data->state == PANEL_STATE_ANIMATION) {
      return WM_UI_HANDLER_CONTINUE;
    }
    else {
      return WM_UI_HANDLER_BREAK;
    }
  }
  
  static void ui_handler_remove_panel(bContext *C, void *userdata)
  {
    Panel *panel = userdata;
  
    panel_activate_state(C, panel, PANEL_STATE_EXIT);
  }
  
  static void panel_activate_state(const bContext *C, Panel *panel, uiHandlePanelState state)
  {
    uiHandlePanelData *data = panel->activedata;
    wmWindow *win = CTX_wm_window(C);
    ARegion *region = CTX_wm_region(C);
  
    if (data && data->state == state) {
      return;
    }
  
    if (state == PANEL_STATE_EXIT || state == PANEL_STATE_ANIMATION) {
      if (data && data->state != PANEL_STATE_ANIMATION) {
        /* XXX:
         * - the panel tabbing function call below (test_add_new_tabs()) has been commented out
         *   "It is too easy to do by accident when reordering panels,
         *   is very hard to control and use, and has no real benefit." - BillRey
         * Aligorith, 2009Sep
         */
        // test_add_new_tabs(region);   // also copies locations of tabs in dragged panel
        check_panel_overlap(region, NULL); /* clears */
      }
  
      panel->flag &= ~PNL_SELECT;
    }
    else {
      panel->flag |= PNL_SELECT;
    }
  
    if (data && data->animtimer) {
      WM_event_remove_timer(CTX_wm_manager(C), win, data->animtimer);
      data->animtimer = NULL;
    }
  
    if (state == PANEL_STATE_EXIT) {
      MEM_freeN(data);
      panel->activedata = NULL;
  
      WM_event_remove_ui_handler(
          &win->modalhandlers, ui_handler_panel, ui_handler_remove_panel, panel, false);
    }
    else {
      if (!data) {
        data = MEM_callocN(sizeof(uiHandlePanelData), "uiHandlePanelData");
        panel->activedata = data;
  
        WM_event_add_ui_handler(
            C, &win->modalhandlers, ui_handler_panel, ui_handler_remove_panel, panel, 0);
      }
  
      if (ELEM(state, PANEL_STATE_ANIMATION, PANEL_STATE_DRAG)) {
        data->animtimer = WM_event_add_timer(CTX_wm_manager(C), win, TIMER, ANIMATION_INTERVAL);
      }
  
      data->state = state;
      data->startx = win->eventstate->x;
      data->starty = win->eventstate->y;
      data->startofsx = panel->ofsx;
      data->startofsy = panel->ofsy;
      data->startsizex = panel->sizex;
      data->startsizey = panel->sizey;
      data->starttime = PIL_check_seconds_timer();
    }
  
    ED_region_tag_redraw(region);
  }
  
  PanelType *UI_paneltype_find(int space_id, int region_id, const char *idname)
  {
    SpaceType *st = BKE_spacetype_from_id(space_id);
    if (st) {
      ARegionType *art = BKE_regiontype_from_id(st, region_id);
      if (art) {
        return BLI_findstring(&art->paneltypes, idname, offsetof(PanelType, idname));
      }
    }
    return NULL;
  }
  