Viewport: imgui_impl_sdl2: Added support for PlatformIO Platform_SetWindowAlpha.

examples/imgui_impl_sdl.cpp

@@ -46,7 +46,7 @@
 #include <SDL_syswm.h>
 #define SDL_HAS_WARP_MOUSE_GLOBAL           SDL_VERSION_ATLEAST(2,0,4)
 #define SDL_HAS_CAPTURE_MOUSE               SDL_VERSION_ATLEAST(2,0,4)
-#define SDL_HAS_WINDOW_OPACITY              SDL_VERSION_ATLEAST(2,0,5)
+#define SDL_HAS_WINDOW_ALPHA                SDL_VERSION_ATLEAST(2,0,5)
 #define SDL_HAS_ALWAYS_ON_TOP               SDL_VERSION_ATLEAST(2,0,5)
 #define SDL_HAS_USABLE_DISPLAY_BOUNDS       SDL_VERSION_ATLEAST(2,0,5)
 #define SDL_HAS_PER_MONITOR_DPI             SDL_VERSION_ATLEAST(2,0,4)
@@ -463,6 +463,14 @@ static void ImGui_ImplSDL2_SetWindowTitle(ImGuiViewport* viewport, const char* t
     SDL_SetWindowTitle(data->Window, title);
 }
 
+#if SDL_HAS_WINDOW_ALPHA
+static void ImGui_ImplSDL2_SetWindowAlpha(ImGuiViewport* viewport, float alpha)
+{
+    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
+    SDL_SetWindowOpacity(data->Window, alpha);
+}
+#endif
+
 static void ImGui_ImplSDL2_SetWindowFocus(ImGuiViewport* viewport)
 {
     ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
@@ -556,6 +564,9 @@ static void ImGui_ImplSDL2_InitPlatformInterface(SDL_Window* window, void* sdl_g
     platform_io.Platform_SetWindowTitle = ImGui_ImplSDL2_SetWindowTitle;
     platform_io.Platform_RenderWindow = ImGui_ImplSDL2_RenderWindow;
     platform_io.Platform_SwapBuffers = ImGui_ImplSDL2_SwapBuffers;
+#if SDL_HAS_WINDOW_ALPHA
+    platform_io.Platform_SetWindowAlpha = ImGui_ImplSDL2_SetWindowAlpha;
+#endif
 #if SDL_HAS_VULKAN
     platform_io.Platform_CreateVkSurface = ImGui_ImplSDL2_CreateVkSurface;
 #endif