text: /*
   * Nuklear - 1.40.8 - public domain
   * no warrenty implied; use at your own risk.
   * authored from 2015-2017 by Micha Mettke
   * emscripten from 2016 by Chris Willcocks
   * OpenGL ES 2.0 from 2017 by Dmitry Hrabrov a.k.a. DeXPeriX
   */
  /*
   * ==============================================================
   *
   *                              API
   *
   * ===============================================================
   */
  #ifndef NK_SDL_GLES2_H_
  #define NK_SDL_GLES2_H_
  
  #include <SDL2/SDL.h>
  #include <SDL2/SDL_opengles2.h>
  
  
  NK_API struct nk_context*   nk_sdl_init(SDL_Window *win);
  NK_API void                 nk_sdl_font_stash_begin(struct nk_font_atlas **atlas);
  NK_API void                 nk_sdl_font_stash_end(void);
  NK_API int                  nk_sdl_handle_event(SDL_Event *evt);
  NK_API void                 nk_sdl_render(enum nk_anti_aliasing , int max_vertex_buffer, int max_element_buffer);
  NK_API void                 nk_sdl_shutdown(void);
  NK_API void                 nk_sdl_device_destroy(void);
  NK_API void                 nk_sdl_device_create(void);
  
  #endif
  
  /*
   * ==============================================================
   *
   *                          IMPLEMENTATION
   *
   * ===============================================================
   */
  #ifdef NK_SDL_GLES2_IMPLEMENTATION
  
  #include <string.h>
  
  struct nk_sdl_device {
      struct nk_buffer cmds;
      struct nk_draw_null_texture null;
      GLuint vbo, ebo;
      GLuint prog;
      GLuint vert_shdr;
      GLuint frag_shdr;
      GLint attrib_pos;
      GLint attrib_uv;
      GLint attrib_col;
      GLint uniform_tex;
      GLint uniform_proj;
      GLuint font_tex;
      GLsizei vs;
      size_t vp, vt, vc;
  };
  
  struct nk_sdl_vertex {
      GLfloat position[2];
      GLfloat uv[2];
      nk_byte col[4];
  };
  
  static struct nk_sdl {
      SDL_Window *win;
      struct nk_sdl_device ogl;
      struct nk_context ctx;
      struct nk_font_atlas atlas;
  } sdl;
  
  
  #define NK_SHADER_VERSION "#version 100\n"
  
  
  NK_API void
  nk_sdl_device_create(void)
  {
      GLint status;
      static const GLchar *vertex_shader =
          NK_SHADER_VERSION
          "uniform mat4 ProjMtx;\n"
          "attribute vec2 Position;\n"
          "attribute vec2 TexCoord;\n"
          "attribute vec4 Color;\n"
          "varying vec2 Frag_UV;\n"
          "varying vec4 Frag_Color;\n"
          "void main() {\n"
          "   Frag_UV = TexCoord;\n"
          "   Frag_Color = Color;\n"
          "   gl_Position = ProjMtx * vec4(Position.xy, 0, 1);\n"
          "}\n";
      static const GLchar *fragment_shader =
          NK_SHADER_VERSION
          "precision mediump float;\n"
          "uniform sampler2D Texture;\n"
          "varying vec2 Frag_UV;\n"
          "varying vec4 Frag_Color;\n"
          "void main(){\n"
          "   gl_FragColor = Frag_Color * texture2D(Texture, Frag_UV);\n"
          "}\n";
  
      struct nk_sdl_device *dev = &sdl.ogl;
      
      nk_buffer_init_default(&dev->cmds);
      dev->prog = glCreateProgram();
      dev->vert_shdr = glCreateShader(GL_VERTEX_SHADER);
      dev->frag_shdr = glCreateShader(GL_FRAGMENT_SHADER);
      glShaderSource(dev->vert_shdr, 1, &vertex_shader, 0);
      glShaderSource(dev->frag_shdr, 1, &fragment_shader, 0);
      glCompileShader(dev->vert_shdr);
      glCompileShader(dev->frag_shdr);
      glGetShaderiv(dev->vert_shdr, GL_COMPILE_STATUS, &status);
      assert(status == GL_TRUE);
      glGetShaderiv(dev->frag_shdr, GL_COMPILE_STATUS, &status);
      assert(status == GL_TRUE);
      glAttachShader(dev->prog, dev->vert_shdr);
      glAttachShader(dev->prog, dev->frag_shdr);
      glLinkProgram(dev->prog);
      glGetProgramiv(dev->prog, GL_LINK_STATUS, &status);
      assert(status == GL_TRUE);
  
  
      dev->uniform_tex = glGetUniformLocation(dev->prog, "Texture");
      dev->uniform_proj = glGetUniformLocation(dev->prog, "ProjMtx");
      dev->attrib_pos = glGetAttribLocation(dev->prog, "Position");
      dev->attrib_uv = glGetAttribLocation(dev->prog, "TexCoord");
      dev->attrib_col = glGetAttribLocation(dev->prog, "Color");
      {
          dev->vs = sizeof(struct nk_sdl_vertex);
          dev->vp = offsetof(struct nk_sdl_vertex, position);
          dev->vt = offsetof(struct nk_sdl_vertex, uv);
          dev->vc = offsetof(struct nk_sdl_vertex, col);
          
          /* Allocate buffers */
          glGenBuffers(1, &dev->vbo);
          glGenBuffers(1, &dev->ebo);
      }
      glBindTexture(GL_TEXTURE_2D, 0);
      glBindBuffer(GL_ARRAY_BUFFER, 0);
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
  }
  
  NK_INTERN void
  nk_sdl_device_upload_atlas(const void *image, int width, int height)
  {
      struct nk_sdl_device *dev = &sdl.ogl;
      glGenTextures(1, &dev->font_tex);
      glBindTexture(GL_TEXTURE_2D, dev->font_tex);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)width, (GLsizei)height, 0,
                  GL_RGBA, GL_UNSIGNED_BYTE, image);
  }
  
  NK_API void
  nk_sdl_device_destroy(void)
  {
      struct nk_sdl_device *dev = &sdl.ogl;
      glDetachShader(dev->prog, dev->vert_shdr);
      glDetachShader(dev->prog, dev->frag_shdr);
      glDeleteShader(dev->vert_shdr);
      glDeleteShader(dev->frag_shdr);
      glDeleteProgram(dev->prog);
      glDeleteTextures(1, &dev->font_tex);
      glDeleteBuffers(1, &dev->vbo);
      glDeleteBuffers(1, &dev->ebo);
      nk_buffer_free(&dev->cmds);
  }
  
  NK_API void
  nk_sdl_render(enum nk_anti_aliasing AA, int max_vertex_buffer, int max_element_buffer)
  {
      struct nk_sdl_device *dev = &sdl.ogl;
      int width, height;
      int display_width, display_height;
      struct nk_vec2 scale;
      GLfloat ortho[4][4] = {
          {2.0f, 0.0f, 0.0f, 0.0f},
          {0.0f,-2.0f, 0.0f, 0.0f},
          {0.0f, 0.0f,-1.0f, 0.0f},
          {-1.0f,1.0f, 0.0f, 1.0f},
      };
      SDL_GetWindowSize(sdl.win, &width, &height);
      SDL_GL_GetDrawableSize(sdl.win, &display_width, &display_height);
      ortho[0][0] /= (GLfloat)width;
      ortho[1][1] /= (GLfloat)height;
  
      scale.x = (float)display_width/(float)width;
      scale.y = (float)display_height/(float)height;
  
      /* setup global state */
      glViewport(0,0,display_width,display_height);
      glEnable(GL_BLEND);
      glBlendEquation(GL_FUNC_ADD);
      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
      glDisable(GL_CULL_FACE);
      glDisable(GL_DEPTH_TEST);
      glEnable(GL_SCISSOR_TEST);
      glActiveTexture(GL_TEXTURE0);
  
      /* setup program */
      glUseProgram(dev->prog);
      glUniform1i(dev->uniform_tex, 0);
      glUniformMatrix4fv(dev->uniform_proj, 1, GL_FALSE, &ortho[0][0]);
      {
          /* convert from command queue into draw list and draw to screen */
          const struct nk_draw_command *cmd;
          void *vertices, *elements;
          const nk_draw_index *offset = NULL;
  
          /* Bind buffers */
          glBindBuffer(GL_ARRAY_BUFFER, dev->vbo);
          glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, dev->ebo);
          
          {
              /* buffer setup */
              glEnableVertexAttribArray((GLuint)dev->attrib_pos);
              glEnableVertexAttribArray((GLuint)dev->attrib_uv);
              glEnableVertexAttribArray((GLuint)dev->attrib_col);
  
              glVertexAttribPointer((GLuint)dev->attrib_pos, 2, GL_FLOAT, GL_FALSE, dev->vs, (void*)dev->vp);
              glVertexAttribPointer((GLuint)dev->attrib_uv, 2, GL_FLOAT, GL_FALSE, dev->vs, (void*)dev->vt);
              glVertexAttribPointer((GLuint)dev->attrib_col, 4, GL_UNSIGNED_BYTE, GL_TRUE, dev->vs, (void*)dev->vc);
          }
  
          glBufferData(GL_ARRAY_BUFFER, max_vertex_buffer, NULL, GL_STREAM_DRAW);
          glBufferData(GL_ELEMENT_ARRAY_BUFFER, max_element_buffer, NULL, GL_STREAM_DRAW);
  
          /* load vertices/elements directly into vertex/element buffer */
          vertices = malloc((size_t)max_vertex_buffer);
          elements = malloc((size_t)max_element_buffer);
          {
              /* fill convert configuration */
              struct nk_convert_config config;
              static const struct nk_draw_vertex_layout_element vertex_layout[] = {
                  {NK_VERTEX_POSITION, NK_FORMAT_FLOAT, NK_OFFSETOF(struct nk_sdl_vertex, position)},
                  {NK_VERTEX_TEXCOORD, NK_FORMAT_FLOAT, NK_OFFSETOF(struct nk_sdl_vertex, uv)},
                  {NK_VERTEX_COLOR, NK_FORMAT_R8G8B8A8, NK_OFFSETOF(struct nk_sdl_vertex, col)},
                  {NK_VERTEX_LAYOUT_END}
              };
              memset(&config, 0, sizeof(config));
              config.vertex_layout = vertex_layout;
              config.vertex_size = sizeof(struct nk_sdl_vertex);
              config.vertex_alignment = NK_ALIGNOF(struct nk_sdl_vertex);
              config.null = dev->null;
              config.circle_segment_count = 22;
              config.curve_segment_count = 22;
              config.arc_segment_count = 22;
              config.global_alpha = 1.0f;
              config.shape_AA = AA;
              config.line_AA = AA;
  
              /* setup buffers to load vertices and elements */
              {struct nk_buffer vbuf, ebuf;
              nk_buffer_init_fixed(&vbuf, vertices, (nk_size)max_vertex_buffer);
              nk_buffer_init_fixed(&ebuf, elements, (nk_size)max_element_buffer);
              nk_convert(&sdl.ctx, &dev->cmds, &vbuf, &ebuf, &config);}
          }
          glBufferSubData(GL_ARRAY_BUFFER, 0, (size_t)max_vertex_buffer, vertices);
          glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, (size_t)max_element_buffer, elements);
          free(vertices);
          free(elements);
  
          /* iterate over and execute each draw command */
          nk_draw_foreach(cmd, &sdl.ctx, &dev->cmds) {
              if (!cmd->elem_count) continue;
              glBindTexture(GL_TEXTURE_2D, (GLuint)cmd->texture.id);
              glScissor((GLint)(cmd->clip_rect.x * scale.x),
                  (GLint)((height - (GLint)(cmd->clip_rect.y + cmd->clip_rect.h)) * scale.y),
                  (GLint)(cmd->clip_rect.w * scale.x),
                  (GLint)(cmd->clip_rect.h * scale.y));
              glDrawElements(GL_TRIANGLES, (GLsizei)cmd->elem_count, GL_UNSIGNED_SHORT, offset);
              offset += cmd->elem_count;
          }
          nk_clear(&sdl.ctx);
          nk_buffer_clear(&dev->cmds);
      }
  
      glUseProgram(0);
      glBindBuffer(GL_ARRAY_BUFFER, 0);
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
  
      glDisable(GL_BLEND);
      glDisable(GL_SCISSOR_TEST);
  }
  
  static void
  nk_sdl_clipboard_paste(nk_handle usr, struct nk_text_edit *edit)
  {
      const char *text = SDL_GetClipboardText();
      if (text) nk_textedit_paste(edit, text, nk_strlen(text));
      (void)usr;
  }
  
  static void
  nk_sdl_clipboard_copy(nk_handle usr, const char *text, int len)
  {
      char *str = 0;
      (void)usr;
      if (!len) return;
      str = (char*)malloc((size_t)len+1);
      if (!str) return;
      memcpy(str, text, (size_t)len);
      str[len] = '\0';
      SDL_SetClipboardText(str);
      free(str);
  }
  
  NK_API struct nk_context*
  nk_sdl_init(SDL_Window *win)
  {
      sdl.win = win;
      nk_init_default(&sdl.ctx, 0);
      sdl.ctx.clip.copy = nk_sdl_clipboard_copy;
      sdl.ctx.clip.paste = nk_sdl_clipboard_paste;
      sdl.ctx.clip.userdata = nk_handle_ptr(0);
      nk_sdl_device_create();
      return &sdl.ctx;
  }
  
  NK_API void
  nk_sdl_font_stash_begin(struct nk_font_atlas **atlas)
  {
      nk_font_atlas_init_default(&sdl.atlas);
      nk_font_atlas_begin(&sdl.atlas);
      *atlas = &sdl.atlas;
  }
  
  NK_API void
  nk_sdl_font_stash_end(void)
  {
      const void *image; int w, h;
      image = nk_font_atlas_bake(&sdl.atlas, &w, &h, NK_FONT_ATLAS_RGBA32);
      nk_sdl_device_upload_atlas(image, w, h);
      nk_font_atlas_end(&sdl.atlas, nk_handle_id((int)sdl.ogl.font_tex), &sdl.ogl.null);
      if (sdl.atlas.default_font)
          nk_style_set_font(&sdl.ctx, &sdl.atlas.default_font->handle);
  
  }
  
  NK_API int
  nk_sdl_handle_event(SDL_Event *evt)
  {
      struct nk_context *ctx = &sdl.ctx;
      if (evt->type == SDL_KEYUP || evt->type == SDL_KEYDOWN) {
          /* key events */
          int down = evt->type == SDL_KEYDOWN;
          const Uint8* state = SDL_GetKeyboardState(0);
          SDL_Keycode sym = evt->key.keysym.sym;
          if (sym == SDLK_RSHIFT || sym == SDLK_LSHIFT)
              nk_input_key(ctx, NK_KEY_SHIFT, down);
          else if (sym == SDLK_DELETE)
              nk_input_key(ctx, NK_KEY_DEL, down);
          else if (sym == SDLK_RETURN)
              nk_input_key(ctx, NK_KEY_ENTER, down);
          else if (sym == SDLK_TAB)
              nk_input_key(ctx, NK_KEY_TAB, down);
          else if (sym == SDLK_BACKSPACE)
              nk_input_key(ctx, NK_KEY_BACKSPACE, down);
          else if (sym == SDLK_HOME) {
              nk_input_key(ctx, NK_KEY_TEXT_START, down);
              nk_input_key(ctx, NK_KEY_SCROLL_START, down);
          } else if (sym == SDLK_END) {
              nk_input_key(ctx, NK_KEY_TEXT_END, down);
              nk_input_key(ctx, NK_KEY_SCROLL_END, down);
          } else if (sym == SDLK_PAGEDOWN) {
              nk_input_key(ctx, NK_KEY_SCROLL_DOWN, down);
          } else if (sym == SDLK_PAGEUP) {
              nk_input_key(ctx, NK_KEY_SCROLL_UP, down);
          } else if (sym == SDLK_z)
              nk_input_key(ctx, NK_KEY_TEXT_UNDO, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_r)
              nk_input_key(ctx, NK_KEY_TEXT_REDO, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_c)
              nk_input_key(ctx, NK_KEY_COPY, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_v)
              nk_input_key(ctx, NK_KEY_PASTE, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_x)
              nk_input_key(ctx, NK_KEY_CUT, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_b)
              nk_input_key(ctx, NK_KEY_TEXT_LINE_START, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_e)
              nk_input_key(ctx, NK_KEY_TEXT_LINE_END, down && state[SDL_SCANCODE_LCTRL]);
          else if (sym == SDLK_UP)
              nk_input_key(ctx, NK_KEY_UP, down);
          else if (sym == SDLK_DOWN)
              nk_input_key(ctx, NK_KEY_DOWN, down);
          else if (sym == SDLK_LEFT) {
              if (state[SDL_SCANCODE_LCTRL])
                  nk_input_key(ctx, NK_KEY_TEXT_WORD_LEFT, down);
              else nk_input_key(ctx, NK_KEY_LEFT, down);
          } else if (sym == SDLK_RIGHT) {
              if (state[SDL_SCANCODE_LCTRL])
                  nk_input_key(ctx, NK_KEY_TEXT_WORD_RIGHT, down);
              else nk_input_key(ctx, NK_KEY_RIGHT, down);
          } else return 0;
          return 1;
      } else if (evt->type == SDL_MOUSEBUTTONDOWN || evt->type == SDL_MOUSEBUTTONUP) {
          /* mouse button */
          int down = evt->type == SDL_MOUSEBUTTONDOWN;
          const int x = evt->button.x, y = evt->button.y;
          if (evt->button.button == SDL_BUTTON_LEFT) {
              if (evt->button.clicks > 1)
                  nk_input_button(ctx, NK_BUTTON_DOUBLE, x, y, down);
              nk_input_button(ctx, NK_BUTTON_LEFT, x, y, down);
          } else if (evt->button.button == SDL_BUTTON_MIDDLE)
              nk_input_button(ctx, NK_BUTTON_MIDDLE, x, y, down);
          else if (evt->button.button == SDL_BUTTON_RIGHT)
              nk_input_button(ctx, NK_BUTTON_RIGHT, x, y, down);
          return 1;
      } else if (evt->type == SDL_MOUSEMOTION) {
          /* mouse motion */
          if (ctx->input.mouse.grabbed) {
              int x = (int)ctx->input.mouse.prev.x, y = (int)ctx->input.mouse.prev.y;
              nk_input_motion(ctx, x + evt->motion.xrel, y + evt->motion.yrel);
          } else nk_input_motion(ctx, evt->motion.x, evt->motion.y);
          return 1;
      } else if (evt->type == SDL_TEXTINPUT) {
          /* text input */
          nk_glyph glyph;
          memcpy(glyph, evt->text.text, NK_UTF_SIZE);
          nk_input_glyph(ctx, glyph);
          return 1;
      } else if (evt->type == SDL_MOUSEWHEEL) {
          /* mouse wheel */
          nk_input_scroll(ctx,nk_vec2((float)evt->wheel.x,(float)evt->wheel.y));
          return 1;
      }
      return 0;
  }
  
  NK_API
  void nk_sdl_shutdown(void)
  {
      nk_font_atlas_clear(&sdl.atlas);
      nk_free(&sdl.ctx);
      nk_sdl_device_destroy();
      memset(&sdl, 0, sizeof(sdl));
  }
  
  #endif
  