Win32: Disable fb transparency when it is broken

On Windows 7, when GLFW framebuffer transparency and the DWM are enabled
but DWM transparency is disabled (i.e. when the Transparency setting is
disabled under Personalization > Color), the contents of the framebuffer
is combined with the last frame using additive blending instead of
replacing the previous contents.

This commit limits GLFW framebuffer transparency on Windows 7 to when
DWM transparency is enabled, removing the previous workaround of setting
a layered window color key that led to rendering artifacts.

Fixes #1512.

(cherry picked from commit 05dd2fa298)

README.md

@@ -120,6 +120,8 @@ information on what to include when reporting a bug.
 
  - Bugfix: Some extension loader headers did not prevent default OpenGL header
    inclusion (#1695)
+ - [Win32] Disabled framebuffer transparency on Windows 7 when DWM windows are
+   opaque (#1512)
  - [Win32] Bugfix: Non-BMP Unicode codepoint input was reported as UTF-16
  - [Cocoa] Changed `EGLNativeWindowType` from `NSView` to `CALayer` (#1169)
  - [Cocoa] Bugfix: Non-BMP Unicode codepoint input was reported as UTF-16

docs/news.dox

@@ -299,6 +299,13 @@ a requirement of the GLFW CMake files.  The GLFW source files do not depend on
 CMake.
 
 
+@subsubsection caveat_fbtransparency_33 Framebuffer transparency requires DWM transparency
+
+GLFW no longer supports framebuffer transparency enabled via @ref
+GLFW_TRANSPARENT_FRAMEBUFFER on Windows 7 if DWM transparency is off
+(the Transparency setting under Personalization > Window Color).
+
+
 @subsection deprecations_33 Deprecations in version 3.3
 
 @subsubsection charmods_callback_33 Character with modifiers callback

docs/window.dox

@@ -234,13 +234,6 @@ alpha channel will be used to combine the framebuffer with the background.  This
 does not affect window decorations.  Possible values are `GLFW_TRUE` and
 `GLFW_FALSE`.
 
-@par
-@win32 GLFW sets a color key for the window to work around repainting issues
-with a transparent framebuffer.  The chosen color value is RGB 255,0,255
-(magenta).  This will make pixels with that exact color fully transparent
-regardless of their alpha values.  If this is a problem, make these pixels any
-other color before buffer swap.
-
 @anchor GLFW_FOCUS_ON_SHOW_hint
 __GLFW_FOCUS_ON_SHOW__ specifies whether the window will be given input
 focus when @ref glfwShowWindow is called. Possible values are `GLFW_TRUE` and `GLFW_FALSE`.

src/win32_init.c

@@ -143,6 +143,8 @@ static GLFWbool loadLibraries(void)
             GetProcAddress(_glfw.win32.dwmapi.instance, "DwmFlush");
         _glfw.win32.dwmapi.EnableBlurBehindWindow = (PFN_DwmEnableBlurBehindWindow)
             GetProcAddress(_glfw.win32.dwmapi.instance, "DwmEnableBlurBehindWindow");
+        _glfw.win32.dwmapi.GetColorizationColor = (PFN_DwmGetColorizationColor)
+            GetProcAddress(_glfw.win32.dwmapi.instance, "DwmGetColorizationColor");
     }
 
     _glfw.win32.shcore.instance = LoadLibraryA("shcore.dll");

src/win32_platform.h

@@ -77,6 +77,9 @@
 #ifndef WM_DWMCOMPOSITIONCHANGED
  #define WM_DWMCOMPOSITIONCHANGED 0x031E
 #endif
+#ifndef WM_DWMCOLORIZATIONCOLORCHANGED
+ #define WM_DWMCOLORIZATIONCOLORCHANGED 0x0320
+#endif
 #ifndef WM_COPYGLOBALDATA
  #define WM_COPYGLOBALDATA 0x0049
 #endif
@@ -247,9 +250,11 @@ typedef BOOL (WINAPI * PFN_AdjustWindowRectExForDpi)(LPRECT,DWORD,BOOL,DWORD,UIN
 typedef HRESULT (WINAPI * PFN_DwmIsCompositionEnabled)(BOOL*);
 typedef HRESULT (WINAPI * PFN_DwmFlush)(VOID);
 typedef HRESULT(WINAPI * PFN_DwmEnableBlurBehindWindow)(HWND,const DWM_BLURBEHIND*);
+typedef HRESULT (WINAPI * PFN_DwmGetColorizationColor)(DWORD*,BOOL*);
 #define DwmIsCompositionEnabled _glfw.win32.dwmapi.IsCompositionEnabled
 #define DwmFlush _glfw.win32.dwmapi.Flush
 #define DwmEnableBlurBehindWindow _glfw.win32.dwmapi.EnableBlurBehindWindow
+#define DwmGetColorizationColor _glfw.win32.dwmapi.GetColorizationColor
 
 // shcore.dll function pointer typedefs
 typedef HRESULT (WINAPI * PFN_SetProcessDpiAwareness)(PROCESS_DPI_AWARENESS);
@@ -375,6 +380,7 @@ typedef struct _GLFWlibraryWin32
         PFN_DwmIsCompositionEnabled     IsCompositionEnabled;
         PFN_DwmFlush                    Flush;
         PFN_DwmEnableBlurBehindWindow   EnableBlurBehindWindow;
+        PFN_DwmGetColorizationColor     GetColorizationColor;
     } dwmapi;
 
     struct {

src/win32_window.c

@@ -377,12 +377,17 @@ static void updateWindowStyles(const _GLFWwindow* window)
 //
 static void updateFramebufferTransparency(const _GLFWwindow* window)
 {
-    BOOL enabled;
+    BOOL composition, opaque;
+    DWORD color;
 
     if (!IsWindowsVistaOrGreater())
         return;
 
-    if (SUCCEEDED(DwmIsCompositionEnabled(&enabled)) && enabled)
+    if (FAILED(DwmIsCompositionEnabled(&composition)) || !composition)
+       return;
+
+    if (IsWindows8OrGreater() ||
+        (SUCCEEDED(DwmGetColorizationColor(&color, &opaque)) && !opaque))
     {
         HRGN region = CreateRectRgn(0, 0, -1, -1);
         DWM_BLURBEHIND bb = {0};
@@ -390,37 +395,18 @@ static void updateFramebufferTransparency(const _GLFWwindow* window)
         bb.hRgnBlur = region;
         bb.fEnable = TRUE;
 
-        if (SUCCEEDED(DwmEnableBlurBehindWindow(window->win32.handle, &bb)))
-        {
-            // Decorated windows don't repaint the transparent background
-            // leaving a trail behind animations
-            // HACK: Making the window layered with a transparency color key
-            //       seems to fix this.  Normally, when specifying
-            //       a transparency color key to be used when composing the
-            //       layered window, all pixels painted by the window in this
-            //       color will be transparent.  That doesn't seem to be the
-            //       case anymore, at least when used with blur behind window
-            //       plus negative region.
-            LONG exStyle = GetWindowLongW(window->win32.handle, GWL_EXSTYLE);
-            exStyle |= WS_EX_LAYERED;
-            SetWindowLongW(window->win32.handle, GWL_EXSTYLE, exStyle);
-
-            // Using a color key not equal to black to fix the trailing
-            // issue.  When set to black, something is making the hit test
-            // not resize with the window frame.
-            SetLayeredWindowAttributes(window->win32.handle,
-                                       RGB(255, 0, 255), 255, LWA_COLORKEY);
-        }
-
+        DwmEnableBlurBehindWindow(window->win32.handle, &bb);
         DeleteObject(region);
     }
     else
     {
-        LONG exStyle = GetWindowLongW(window->win32.handle, GWL_EXSTYLE);
-        exStyle &= ~WS_EX_LAYERED;
-        SetWindowLongW(window->win32.handle, GWL_EXSTYLE, exStyle);
-        RedrawWindow(window->win32.handle, NULL, NULL,
-                     RDW_ERASE | RDW_INVALIDATE | RDW_FRAME);
+        // HACK: Disable framebuffer transparency on Windows 7 when the
+        //       colorization color is opaque, because otherwise the window
+        //       contents is blended additively with the previous frame instead
+        //       of replacing it
+        DWM_BLURBEHIND bb = {0};
+        bb.dwFlags = DWM_BB_ENABLE;
+        DwmEnableBlurBehindWindow(window->win32.handle, &bb);
     }
 }
 
@@ -1097,6 +1083,7 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
         }
 
         case WM_DWMCOMPOSITIONCHANGED:
+        case WM_DWMCOLORIZATIONCOLORCHANGED:
         {
             if (window->win32.transparent)
                 updateFramebufferTransparency(window);
@@ -1821,7 +1808,8 @@ int _glfwPlatformWindowHovered(_GLFWwindow* window)
 
 int _glfwPlatformFramebufferTransparent(_GLFWwindow* window)
 {
-    BOOL enabled;
+    BOOL composition, opaque;
+    DWORD color;
 
     if (!window->win32.transparent)
         return GLFW_FALSE;
@@ -1829,7 +1817,20 @@ int _glfwPlatformFramebufferTransparent(_GLFWwindow* window)
     if (!IsWindowsVistaOrGreater())
         return GLFW_FALSE;
 
-    return SUCCEEDED(DwmIsCompositionEnabled(&enabled)) && enabled;
+    if (FAILED(DwmIsCompositionEnabled(&composition)) || !composition)
+        return GLFW_FALSE;
+
+    if (!IsWindows8OrGreater())
+    {
+        // HACK: Disable framebuffer transparency on Windows 7 when the
+        //       colorization color is opaque, because otherwise the window
+        //       contents is blended additively with the previous frame instead
+        //       of replacing it
+        if (FAILED(DwmGetColorizationColor(&color, &opaque)) || opaque)
+            return GLFW_FALSE;
+    }
+
+    return GLFW_TRUE;
 }
 
 void _glfwPlatformSetWindowResizable(_GLFWwindow* window, GLFWbool enabled)