text: /*
  * Copyright 2017 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
  
  #include "tools/viewer/ImGuiLayer.h"
  
  #include "include/core/SkCanvas.h"
  #include "include/core/SkImage.h"
  #include "include/core/SkPixmap.h"
  #include "include/core/SkSurface.h"
  #include "include/core/SkSwizzle.h"
  #include "include/core/SkTime.h"
  #include "include/core/SkVertices.h"
  
  #include "imgui.h"
  
  #include <stdlib.h>
  #include <map>
  
  using namespace sk_app;
  
  ImGuiLayer::ImGuiLayer() {
      // ImGui initialization:
      ImGui::CreateContext();
      ImGuiIO& io = ImGui::GetIO();
  
      // Keymap...
      io.KeyMap[ImGuiKey_Tab] = (int)Window::Key::kTab;
      io.KeyMap[ImGuiKey_LeftArrow] = (int)Window::Key::kLeft;
      io.KeyMap[ImGuiKey_RightArrow] = (int)Window::Key::kRight;
      io.KeyMap[ImGuiKey_UpArrow] = (int)Window::Key::kUp;
      io.KeyMap[ImGuiKey_DownArrow] = (int)Window::Key::kDown;
      io.KeyMap[ImGuiKey_PageUp] = (int)Window::Key::kPageUp;
      io.KeyMap[ImGuiKey_PageDown] = (int)Window::Key::kPageDown;
      io.KeyMap[ImGuiKey_Home] = (int)Window::Key::kHome;
      io.KeyMap[ImGuiKey_End] = (int)Window::Key::kEnd;
      io.KeyMap[ImGuiKey_Delete] = (int)Window::Key::kDelete;
      io.KeyMap[ImGuiKey_Backspace] = (int)Window::Key::kBack;
      io.KeyMap[ImGuiKey_Enter] = (int)Window::Key::kOK;
      io.KeyMap[ImGuiKey_Escape] = (int)Window::Key::kEscape;
      io.KeyMap[ImGuiKey_A] = (int)Window::Key::kA;
      io.KeyMap[ImGuiKey_C] = (int)Window::Key::kC;
      io.KeyMap[ImGuiKey_V] = (int)Window::Key::kV;
      io.KeyMap[ImGuiKey_X] = (int)Window::Key::kX;
      io.KeyMap[ImGuiKey_Y] = (int)Window::Key::kY;
      io.KeyMap[ImGuiKey_Z] = (int)Window::Key::kZ;
  
      int w, h;
      unsigned char* pixels;
      io.Fonts->GetTexDataAsAlpha8(&pixels, &w, &h);
      SkImageInfo info = SkImageInfo::MakeA8(w, h);
      SkPixmap pmap(info, pixels, info.minRowBytes());
      SkMatrix localMatrix = SkMatrix::MakeScale(1.0f / w, 1.0f / h);
      auto fontImage = SkImage::MakeFromRaster(pmap, nullptr, nullptr);
      auto fontShader = fontImage->makeShader(&localMatrix);
      fFontPaint.setShader(fontShader);
      fFontPaint.setColor(SK_ColorWHITE);
      fFontPaint.setFilterQuality(kLow_SkFilterQuality);
      io.Fonts->TexID = &fFontPaint;
  }
  
  ImGuiLayer::~ImGuiLayer() {
      ImGui::DestroyContext();
  }
  
  void ImGuiLayer::onAttach(Window* window) {
      fWindow = window;
  }
  
  bool ImGuiLayer::onMouse(int x, int y, InputState state, ModifierKey modifiers) {
      ImGuiIO& io = ImGui::GetIO();
      io.MousePos.x = static_cast<float>(x);
      io.MousePos.y = static_cast<float>(y);
      if (InputState::kDown == state) {
          io.MouseDown[0] = true;
      } else if (InputState::kUp == state) {
          io.MouseDown[0] = false;
      }
      return io.WantCaptureMouse;
  }
  
  bool ImGuiLayer::onMouseWheel(float delta, ModifierKey modifiers) {
      ImGuiIO& io = ImGui::GetIO();
      io.MouseWheel += delta;
      return true;
  }
  
  void ImGuiLayer::skiaWidget(const ImVec2& size, SkiaWidgetFunc func) {
      intptr_t funcIndex = fSkiaWidgetFuncs.count();
      fSkiaWidgetFuncs.push_back(func);
      ImGui::Image((ImTextureID)funcIndex, size);
  }
  
  void ImGuiLayer::onPrePaint() {
      // Update ImGui input
      ImGuiIO& io = ImGui::GetIO();
  
      static double previousTime = 0.0;
      double currentTime = SkTime::GetSecs();
      io.DeltaTime = static_cast<float>(currentTime - previousTime);
      previousTime = currentTime;
  
      io.DisplaySize.x = static_cast<float>(fWindow->width());
      io.DisplaySize.y = static_cast<float>(fWindow->height());
  
      io.KeyAlt = io.KeysDown[static_cast<int>(Window::Key::kOption)];
      io.KeyCtrl = io.KeysDown[static_cast<int>(Window::Key::kCtrl)];
      io.KeyShift = io.KeysDown[static_cast<int>(Window::Key::kShift)];
  
      ImGui::NewFrame();
  }
  
  void ImGuiLayer::onPaint(SkSurface* surface) {
      // This causes ImGui to rebuild vertex/index data based on all immediate-mode commands
      // (widgets, etc...) that have been issued
      ImGui::Render();
  
      // Then we fetch the most recent data, and convert it so we can render with Skia
      const ImDrawData* drawData = ImGui::GetDrawData();
      SkTDArray<SkPoint> pos;
      SkTDArray<SkPoint> uv;
      SkTDArray<SkColor> color;
  
      auto canvas = surface->getCanvas();
  
      for (int i = 0; i < drawData->CmdListsCount; ++i) {
          const ImDrawList* drawList = drawData->CmdLists[i];
  
          // De-interleave all vertex data (sigh), convert to Skia types
          pos.rewind(); uv.rewind(); color.rewind();
          for (int j = 0; j < drawList->VtxBuffer.size(); ++j) {
              const ImDrawVert& vert = drawList->VtxBuffer[j];
              pos.push_back(SkPoint::Make(vert.pos.x, vert.pos.y));
              uv.push_back(SkPoint::Make(vert.uv.x, vert.uv.y));
              color.push_back(vert.col);
          }
          // ImGui colors are RGBA
          SkSwapRB(color.begin(), color.begin(), color.count());
  
          int indexOffset = 0;
  
          // Draw everything with canvas.drawVertices...
          for (int j = 0; j < drawList->CmdBuffer.size(); ++j) {
              const ImDrawCmd* drawCmd = &drawList->CmdBuffer[j];
  
              SkAutoCanvasRestore acr(canvas, true);
  
              // TODO: Find min/max index for each draw, so we know how many vertices (sigh)
              if (drawCmd->UserCallback) {
                  drawCmd->UserCallback(drawList, drawCmd);
              } else {
                  intptr_t idIndex = (intptr_t)drawCmd->TextureId;
                  if (idIndex < fSkiaWidgetFuncs.count()) {
                      // Small image IDs are actually indices into a list of callbacks. We directly
                      // examing the vertex data to deduce the image rectangle, then reconfigure the
                      // canvas to be clipped and translated so that the callback code gets to use
                      // Skia to render a widget in the middle of an ImGui panel.
                      ImDrawIdx rectIndex = drawList->IdxBuffer[indexOffset];
                      SkPoint tl = pos[rectIndex], br = pos[rectIndex + 2];
                      canvas->clipRect(SkRect::MakeLTRB(tl.fX, tl.fY, br.fX, br.fY));
                      canvas->translate(tl.fX, tl.fY);
                      fSkiaWidgetFuncs[idIndex](canvas);
                  } else {
                      SkPaint* paint = static_cast<SkPaint*>(drawCmd->TextureId);
                      SkASSERT(paint);
  
                      canvas->clipRect(SkRect::MakeLTRB(drawCmd->ClipRect.x, drawCmd->ClipRect.y,
                                                        drawCmd->ClipRect.z, drawCmd->ClipRect.w));
                      auto vertices = SkVertices::MakeCopy(SkVertices::kTriangles_VertexMode,
                                                           drawList->VtxBuffer.size(),
                                                           pos.begin(), uv.begin(), color.begin(),
                                                           drawCmd->ElemCount,
                                                           drawList->IdxBuffer.begin() + indexOffset);
                      canvas->drawVertices(vertices, SkBlendMode::kModulate, *paint);
                  }
                  indexOffset += drawCmd->ElemCount;
              }
          }
      }
  
      fSkiaWidgetFuncs.reset();
  }
  
  bool ImGuiLayer::onKey(sk_app::Window::Key key, InputState state, ModifierKey modifiers) {
      ImGuiIO& io = ImGui::GetIO();
      io.KeysDown[static_cast<int>(key)] = (InputState::kDown == state);
      return io.WantCaptureKeyboard;
  }
  
  bool ImGuiLayer::onChar(SkUnichar c, ModifierKey modifiers) {
      ImGuiIO& io = ImGui::GetIO();
      if (io.WantTextInput) {
          if (c > 0 && c < 0x10000) {
              io.AddInputCharacter(c);
          }
          return true;
      }
      return false;
  }
  