3 files changed, 28 insertions, 0 deletions
diff --git a/include/cru/platform/graphics/Image.h b/include/cru/platform/graphics/Image.h
index 51e27678..de3b32d5 100644
--- a/include/cru/platform/graphics/Image.h
+++ b/include/cru/platform/graphics/Image.h
@@ -6,5 +6,21 @@ struct CRU_PLATFORM_GRAPHICS_API IImage : public virtual IGraphicsResource {
   virtual float GetWidth() = 0;
   virtual float GetHeight() = 0;
   virtual std::unique_ptr<IImage> CreateWithRect(const Rect& rect) = 0;
+
+  /**
+   * \brief Create a painter for this image.
+   * \remarks Not all image could create a painter. If not this method will
+   * throw. Currently we only ensure images returned by
+   * IImageFactory::CreateBitmap or CloneToBitmap can create a painter.
+   * \todo Implement on Windows.
+   */
+  virtual std::unique_ptr<IPainter> CreatePainter() = 0;
+
+  /**
+   * \brief Create a bitmap image with the same pixels as this image's.
+   * \remarks This method can be used to create a bitmap image, so you can draw
+   * on the new bitmap, if the original image can't be directly painted.
+   */
+  virtual std::unique_ptr<IImage> CloneToBitmap();
 };
 }  // namespace cru::platform::graphics
diff --git a/include/cru/platform/graphics/ImageFactory.h b/include/cru/platform/graphics/ImageFactory.h
index 2a7902b2..d2c2a468 100644
--- a/include/cru/platform/graphics/ImageFactory.h
+++ b/include/cru/platform/graphics/ImageFactory.h
@@ -7,5 +7,13 @@ namespace cru::platform::graphics {
 struct CRU_PLATFORM_GRAPHICS_API IImageFactory
     : public virtual IGraphicsResource {
   virtual std::unique_ptr<IImage> DecodeFromStream(io::Stream* stream) = 0;
+
+  /**
+   * \brief Create an empty bitmap with given width and height.
+   * \remarks Implementation should ensure that the bitmap supports alpha
+   * channel. It had better be in 32-bit rgba format.
+   * \todo Implement on Windows.
+   */
+  virtual std::unique_ptr<IImage> CreateBitmap(int width, int height) = 0;
 };
 }  // namespace cru::platform::graphics
diff --git a/include/cru/platform/graphics/Painter.h b/include/cru/platform/graphics/Painter.h
index 38ff8849..4268133e 100644
--- a/include/cru/platform/graphics/Painter.h
+++ b/include/cru/platform/graphics/Painter.h
@@ -3,6 +3,10 @@
 
 namespace cru::platform::graphics {
 
+/**
+ * \brief Painter is a object to paint on something like window, bitmap and etc.
+ * \remarks Remember to call EndDraw() when you are done with painting.
+ */
 struct CRU_PLATFORM_GRAPHICS_API IPainter : virtual IPlatformResource {
   virtual Matrix GetTransform() = 0;
   virtual void SetTransform(const Matrix& matrix) = 0;