Added image wrapper (#74)

Raw.image and sdl2/gl example "image"

Wrappers should be backend-specific due to different handling of `userTextureIDPtr`.

src/DearImGui/Raw.hs

@@ -105,6 +105,7 @@ module DearImGui.Raw
   , smallButton
   , invisibleButton
   , arrowButton
+  , image
   , checkbox
   , progressBar
   , bullet
@@ -558,6 +559,31 @@ arrowButton strIdPtr dir = liftIO do
   (0 /=) <$> [C.exp| bool { ArrowButton($(char* strIdPtr), $(ImGuiDir dir)) } |]
 
 
+-- | Image Area to draw a texture
+--
+-- Wraps @ImGui::Image()
+--
+-- For OpenGL: The userTextureIDPtr points to the texture memory (eg. 0x0x0000000000000001), it is the number from glBindTexture.
+-- Eg:
+-- glBindTexture GL_TEXTURE_2D $ textureID texture
+-- -- fill textureID
+-- image (intPtrToPtr $ fromIntegral textureID) (ImVec2 500 500)(ImVec2 0 0)(ImVec2 1 1)(ImVec4 1 1 1 1)(ImVec4 0 0 0 0)
+--
+-- See https://github.com/ocornut/imgui/wiki/Image-Loading-and-Displaying-Examples#About-texture-coordinates and under examples/sdl/Image.hs
+image :: (MonadIO m) => Ptr ()->  Ptr ImVec2 -> Ptr ImVec2 -> Ptr ImVec2 -> Ptr ImVec4 -> Ptr ImVec4 -> m()
+image userTextureIDPtr sizePtr uv0Ptr uv1Ptr tintColPtr borderColPtr = liftIO do
+  [C.exp| void { 
+    Image(
+      $(void* userTextureIDPtr), 
+      *$(ImVec2* sizePtr),
+      *$(ImVec2* uv0Ptr),
+      *$(ImVec2* uv1Ptr),
+      *$(ImVec4* tintColPtr),
+      *$(ImVec4* borderColPtr)
+    )
+  } |]
+
+
 -- | Wraps @ImGui::Checkbox()@.
 checkbox :: (MonadIO m) => CString -> Ptr CBool -> m Bool
 checkbox labelPtr boolPtr = liftIO do