Implemented alpha blending for WIN32. I believe that I did it in a way that is compatible even with Windows 95, but please let me know if you have any concerns. Cygwin not tested, but hopefully OK.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@5430 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

5 files changed, 94 insertions, 22 deletions

diff --git a/CHANGES b/CHANGES
index 9efe11724..dd16b6fb4 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,5 +1,6 @@
 CHANGES IN FLTK 1.1.8
 
+	- Implemented alpha blending for WIN32
 	- Updated documentation (STR #1420, STR #1421)
 	- Fixed font caching issue (STR #1415)
 	- Fixed crash in fl_file_chooser (STR #1410)
diff --git a/FL/fl_draw.H b/FL/fl_draw.H
index bfd3ef26f..509826ef4 100644
--- a/FL/fl_draw.H
+++ b/FL/fl_draw.H
@@ -178,6 +178,7 @@ typedef void (*Fl_Draw_Image_Cb)(void*,int,int,int,uchar*);
 FL_EXPORT void fl_draw_image(Fl_Draw_Image_Cb, void*, int,int,int,int, int delta=3);
 FL_EXPORT void fl_draw_image_mono(Fl_Draw_Image_Cb, void*, int,int,int,int, int delta=1);
 FL_EXPORT void fl_rectf(int x, int y, int w, int h, uchar r, uchar g, uchar b);
+FL_EXPORT char fl_can_do_alpha_blending();
 
 FL_EXPORT uchar *fl_read_image(uchar *p, int x,int y, int w, int h, int alpha=0);
 
diff --git a/src/Fl_Double_Window.cxx b/src/Fl_Double_Window.cxx
index 54fd2b935..4e5f7bf1b 100644
--- a/src/Fl_Double_Window.cxx
+++ b/src/Fl_Double_Window.cxx
@@ -76,6 +76,28 @@ void Fl_Double_Window::show() {
 // Code used to switch output to an off-screen window.  See macros in
 // win32.H which save the old state in local variables.
 
+typedef struct { BYTE a; BYTE b; BYTE c; BYTE d; } FL_BLENDFUNCTION;
+typedef BOOL (WINAPI* fl_alpha_blend_func)
+    (HDC,int,int,int,int,HDC,int,int,int,int,FL_BLENDFUNCTION);
+static fl_alpha_blend_func fl_alpha_blend = NULL;
+
+/*
+ * This function checks if the version of MSWindows that we
+ * curently run on supports alpha blending for bitmap transfers
+ * and finds the required function if so.
+ */
+char fl_can_do_alpha_blending() {
+  static char been_here = 0;
+  static char can_do = 0;
+  if (been_here) return can_do;
+  HMODULE hMod = LoadLibrary("MSIMG32.DLL");
+  if (!hMod) return 0;
+  fl_alpha_blend = (fl_alpha_blend_func)GetProcAddress(hMod, "AlphaBlend");
+  if (!fl_alpha_blend) return 0;
+  can_do = 1;
+  return 1;
+}
+
 HDC fl_makeDC(HBITMAP bitmap) {
   HDC new_gc = CreateCompatibleDC(fl_gc);
   SetTextAlign(new_gc, TA_BASELINE|TA_LEFT);
@@ -88,10 +110,15 @@ HDC fl_makeDC(HBITMAP bitmap) {
 }
 
 void fl_copy_offscreen(int x,int y,int w,int h,HBITMAP bitmap,int srcx,int srcy) {
+  static FL_BLENDFUNCTION blendfunc = { 0, 0, 255, 1};
+
   HDC new_gc = CreateCompatibleDC(fl_gc);
   int save = SaveDC(new_gc);
   SelectObject(new_gc, bitmap);
-  BitBlt(fl_gc, x, y, w, h, new_gc, srcx, srcy, SRCCOPY);
+  if (fl_can_do_alpha_blending()) 
+    fl_alpha_blend(fl_gc, x, y, w, h, new_gc, srcx, srcy, w, h, blendfunc);
+  else
+    BitBlt(fl_gc, x, y, w, h, new_gc, srcx, srcy, SRCCOPY);
   RestoreDC(new_gc, save);
   DeleteDC(new_gc);
 }
@@ -100,6 +127,10 @@ extern void fl_restore_clip();
 
 #elif defined(__APPLE_QD__)
 
+char fl_can_do_alpha_blending() {
+  return 0;
+}
+
 GWorldPtr fl_create_offscreen(int w, int h) {
   GWorldPtr gw;
   Rect bounds;
@@ -173,6 +204,10 @@ extern void fl_restore_clip();
 
 #elif defined(__APPLE_QUARTZ__)
 
+char fl_can_do_alpha_blending() {
+  return 1;
+}
+
 Fl_Offscreen fl_create_offscreen(int w, int h) {
   void *data = calloc(w*h,4);
   CGColorSpaceRef lut = CGColorSpaceCreateDeviceRGB();
@@ -254,6 +289,13 @@ void fl_end_offscreen() {
 
 extern void fl_restore_clip();
 
+#else // X11
+
+// maybe someone feels inclined to implement alpha blending on X11?
+char fl_can_do_alpha_blending() {
+  return 0;
+}
+
 #endif
 
 // Fl_Overlay_Window relies on flush(1) copying the back buffer to the
diff --git a/src/Fl_Image.cxx b/src/Fl_Image.cxx
index 60e56078a..f1247512a 100644
--- a/src/Fl_Image.cxx
+++ b/src/Fl_Image.cxx
@@ -352,7 +352,7 @@ void Fl_RGB_Image::draw(int XP, int YP, int WP, int HP, int cx, int cy) {
     fl_begin_offscreen((Fl_Offscreen)id);
     fl_draw_image(array, 0, 0, w(), h(), d(), ld());
     fl_end_offscreen();
-    if (d() == 2 || d() == 4) {
+    if (d() == 2 || d() == 4 && !fl_can_do_alpha_blending()) {
       mask = fl_create_alphamask(w(), h(), d(), ld(), array);
     }
 #endif
diff --git a/src/fl_draw_image_win32.cxx b/src/fl_draw_image_win32.cxx
index a47cbfc10..f55ca9720 100644
--- a/src/fl_draw_image_win32.cxx
+++ b/src/fl_draw_image_win32.cxx
@@ -112,13 +112,17 @@ static void monodither(uchar* to, const uchar* from, int w, int delta) {
 #endif // USE_COLORMAP
 
 static void innards(const uchar *buf, int X, int Y, int W, int H,
-		    int delta, int linedelta, int mono,
+		    int delta, int linedelta, int depth,
 		    Fl_Draw_Image_Cb cb, void* userdata)
 {
 #if USE_COLORMAP
   char indexed = (fl_palette != 0);
 #endif
 
+  if (depth==0) depth = 3;
+  if (indexed || !fl_can_do_alpha_blending()) 
+    depth = (depth-1)|1;
+
   if (!linedelta) linedelta = W*delta;
 
   int x, y, w, h;
@@ -144,7 +148,7 @@ static void innards(const uchar *buf, int X, int Y, int W, int H,
     }
   } else
 #endif
-  if (mono) {
+  if (depth<3) {
     for (int i=0; i<256; i++) {
       bmi.bmiColors[i].rgbBlue = (uchar)i;
       bmi.bmiColors[i].rgbGreen = (uchar)i;
@@ -154,11 +158,11 @@ static void innards(const uchar *buf, int X, int Y, int W, int H,
   }
   bmi.bmiHeader.biWidth = w;
 #if USE_COLORMAP
-  bmi.bmiHeader.biBitCount = mono|indexed ? 8 : 24;
-  int pixelsize = mono|indexed ? 1 : 3;
+  bmi.bmiHeader.biBitCount = indexed ? 8 : depth*8;
+  int pixelsize = indexed ? 1 : depth;
 #else
-  bmi.bmiHeader.biBitCount = mono ? 8 : 24;
-  int pixelsize = mono ? 1 : 3;
+  bmi.bmiHeader.biBitCount = depth*8;
+  int pixelsize = depth;
 #endif
   int linesize = (pixelsize*w+3)&~3;
   
@@ -200,22 +204,44 @@ static void innards(const uchar *buf, int X, int Y, int W, int H,
       uchar *to = (uchar*)buffer+(blocking-k-1)*linesize;
 #if USE_COLORMAP
       if (indexed) {
-	if (mono)
+	if (depth<3)
 	  monodither(to, from, w, delta);
 	else 
 	  dither(to, from, w, delta);
 	to += w;
       } else
 #endif
-      if (mono) {
-	for (int i=w; i--; from += delta) *to++ = *from;
-      } else {
-	for (int i=w; i--; from += delta, to += 3) {
-	  uchar r = from[0];
-	  to[0] = from[2];
-	  to[1] = from[1];
-	  to[2] = r;
-        }
+      {
+        int i;
+        switch (depth) {
+          case 1: 
+            for (i=w; i--; from += delta) *to++ = *from;
+            break;
+          case 2:
+            for (i=w; i--; from += delta) {
+              *to++ = *from;
+              *to++ = *from;
+            }
+            break;
+          case 3:
+	    for (i=w; i--; from += delta, to += 3) {
+	      uchar r = from[0];
+	      to[0] = from[2];
+	      to[1] = from[1];
+	      to[2] = r;
+            }
+            break;          
+          case 4:
+	    for (i=w; i--; from += delta, to += 4) {
+              uchar a = from[3];
+	      uchar r = from[0];
+	      to[0] = (from[2]*a)>>8;
+	      to[1] = (from[1]*a)>>8;
+	      to[2] = (r*a)>>8;
+	      to[3] = from[3];
+            }
+            break;          
+        }            
       }
     }
     SetDIBitsToDevice(fl_gc, x, y+j-k, w, k, 0, 0, 0, k,
@@ -230,19 +256,21 @@ static void innards(const uchar *buf, int X, int Y, int W, int H,
   }
 }
 
+static int fl_abs(int v) { return v<0 ? -v : v; }
+
 void fl_draw_image(const uchar* buf, int x, int y, int w, int h, int d, int l){
-  innards(buf,x,y,w,h,d,l,(d<3&&d>-3),0,0);
+  innards(buf,x,y,w,h,d,l,fl_abs(d),0,0);
 }
 void fl_draw_image(Fl_Draw_Image_Cb cb, void* data,
 		   int x, int y, int w, int h,int d) {
-  innards(0,x,y,w,h,d,0,(d<3&&d>-3),cb,data);
+  innards(0,x,y,w,h,d,0,fl_abs(d),cb,data);
 }
 void fl_draw_image_mono(const uchar* buf, int x, int y, int w, int h, int d, int l){
-  innards(buf,x,y,w,h,d,l,1,0,0);
+  innards(buf,x,y,w,h,d,l,fl_abs(d),0,0);
 }
 void fl_draw_image_mono(Fl_Draw_Image_Cb cb, void* data,
 		   int x, int y, int w, int h,int d) {
-  innards(0,x,y,w,h,d,0,1,cb,data);
+  innards(0,x,y,w,h,d,0,fl_abs(d),cb,data);
 }
 
 void fl_rectf(int x, int y, int w, int h, uchar r, uchar g, uchar b) {