Add GraphicsContext format hint member

This helps in setting the right paint color when using GraphicsContexts
based on non RGB images.

src/app/script/graphics_context.cpp

@@ -29,6 +29,36 @@
 namespace app {
 namespace script {
 
+void GraphicsContext::color(gfx::Color color)
+{
+  switch (m_formatHint) {
+    case doc::PixelFormat::IMAGE_GRAYSCALE:
+      // Underlying SkSurface's color type is kR8G8_unorm_SkColorType, then we
+      // must transform the color to set R to the gray level and G to the
+      // alpha level.
+      color = gfx::rgba(gfx::getr(color), gfx::geta(color), 0);
+      break;
+    case doc::PixelFormat::IMAGE_INDEXED: {
+      // Underlying SkSurface's color type is kAlpha_8_SkColorType, then we
+      // must transform the color to set Alpha to the corresponding index.
+      int i = get_current_palette()->findExactMatch(gfx::getr(color),
+                                                    gfx::getg(color),
+                                                    gfx::getb(color),
+                                                    gfx::geta(color), -1);
+      if (i == -1) {
+        i = get_current_palette()->findBestfit(gfx::getr(color),
+                                              gfx::getg(color),
+                                              gfx::getb(color),
+                                              gfx::geta(color), -1);
+      }
+
+      color = gfx::rgba(0, 0, 0, i);
+      break;
+    }
+  }
+  m_paint.color(color);
+}
+
 void GraphicsContext::fillText(const std::string& text, int x, int y)
 {
   if (auto theme = skin::SkinTheme::instance()) {
@@ -59,7 +89,7 @@ void GraphicsContext::drawImage(const doc::Image* img, int x, int y)
     return;
   }
 
-   drawImage(img, img->bounds(), gfx::Rect(x, y, img->size().w, img->size().h));
+  drawImage(img, img->bounds(), gfx::Rect(x, y, img->size().w, img->size().h));
 }
 
 void GraphicsContext::drawImage(const doc::Image* img,
@@ -429,7 +459,23 @@ int GraphicsContext_set_antialias(lua_State* L)
 int GraphicsContext_get_color(lua_State* L)
 {
   auto gc = get_obj<GraphicsContext>(L, 1);
-  push_obj(L, color_utils::color_from_ui(gc->color()));
+
+  const gfx::Color gcColor = gc->color();
+  app::Color color;
+  switch (gc->formatHint()) {
+    case IMAGE_GRAYSCALE:
+      color = app::Color::fromGray(gfx::getr(gcColor), gfx::geta(gcColor));
+      break;
+    case IMAGE_INDEXED: {
+      const int i = gfx::geta(gcColor);
+      color = app::Color::fromIndex(i);
+      break;
+    }
+    case IMAGE_RGB:
+    default:
+      color = color_utils::color_from_ui(gcColor);
+  }
+  push_obj(L, color);
   return 1;
 }
 

src/app/script/graphics_context.h

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "doc/palette.h"
+#include "doc/pixel_format.h"
 #include "gfx/path.h"
 #include "os/paint.h"
 #include "os/surface.h"
@@ -31,7 +32,10 @@ private:
   };
 
 public:
-  GraphicsContext(const os::SurfaceRef& surface, int uiscale) : m_surface(surface), m_uiscale(uiscale) { }
+  GraphicsContext(const os::SurfaceRef& surface,
+                  int uiscale,
+                  doc::PixelFormat formatHint = doc::PixelFormat::IMAGE_RGB)
+    : m_surface(surface), m_uiscale(uiscale), m_formatHint(formatHint) { }
   GraphicsContext(const GraphicsContext& gc) {
     m_surface = gc.m_surface;
     m_font = gc.m_font;
@@ -39,6 +43,7 @@ public:
     m_palette = gc.m_palette;
     m_path = gc.m_path;
     m_saved = gc.m_saved;
+    m_formatHint = gc.m_formatHint;
     m_uiscale = gc.m_uiscale;
   }
   GraphicsContext(GraphicsContext&& gc) noexcept {
@@ -46,6 +51,7 @@ public:
     std::swap(m_paint, gc.m_paint);
     std::swap(m_font, gc.m_font);
     std::swap(m_path, gc.m_path);
+    m_formatHint = gc.m_formatHint;
     m_uiscale = gc.m_uiscale;
   }
 
@@ -77,7 +83,7 @@ public:
   void antialias(bool value) { m_paint.antialias(value); }
 
   gfx::Color color() const { return m_paint.color(); }
-  void color(gfx::Color color) { m_paint.color(color); }
+  void color(gfx::Color color);
 
   float strokeWidth() const { return m_paint.strokeWidth(); }
   void strokeWidth(float value) { m_paint.strokeWidth(value); }
@@ -142,6 +148,10 @@ public:
     return m_uiscale;
   }
 
+  doc::PixelFormat formatHint() const {
+    return m_formatHint;
+  }
+
 private:
   os::SurfaceRef m_surface = nullptr;
   // Keeps the UI Scale currently in use when canvas autoScaling is enabled.
@@ -151,6 +161,8 @@ private:
   gfx::Path m_path;
   std::stack<State> m_saved;
   doc::Palette* m_palette = nullptr;
+  // Pixel format hint about the underlying pixels wrapped by m_surface.
+  doc::PixelFormat m_formatHint = doc::PixelFormat::IMAGE_RGB;
 };
 
 } // namespace script

src/app/script/image_class.cpp

@@ -757,7 +757,7 @@ int Image_get_context(lua_State* L)
 
   if (!obj->context) {
     auto surface = wrap_docimage_in_surface(obj->image(L));
-    obj->context = std::make_unique<GraphicsContext>(surface, ui::guiscale());
+    obj->context = std::make_unique<GraphicsContext>(surface, ui::guiscale(), obj->image(L)->pixelFormat());
   }
 
   push_obj(L, *obj->context);