comctl32: Pre-multiply static control bitmap image by alpha for GdiAlphaBlend.

dlls/comctl32/static.c

@@ -203,6 +203,17 @@ static HBITMAP create_alpha_bitmap( HBITMAP hbitmap )
             DeleteObject( alpha );
             alpha = 0;
         }
+        else
+        {
+            /* pre-multiply by alpha */
+            for (i = 0, ptr = bits; i < bm.bmWidth * bm.bmHeight; i++, ptr += 4)
+            {
+                unsigned int alpha = ptr[3];
+                ptr[0] = (ptr[0] * alpha + 127) / 255;
+                ptr[1] = (ptr[1] * alpha + 127) / 255;
+                ptr[2] = (ptr[2] * alpha + 127) / 255;
+            }
+        }
     }
 
     DeleteDC( hdc );

dlls/comctl32/tests/static.c

@@ -165,7 +165,6 @@ static void test_image(HBITMAP image, BOOL is_dib, BOOL is_premult, BOOL is_alph
         ok(bm.bmBits != NULL, "bmBits is NULL\n");
         memcpy(bits, bm.bmBits, 4);
         if (is_premult)
-            todo_wine
             ok(bits[0] == 0x05 &&  bits[1] == 0x09 &&  bits[2] == 0x0e && bits[3] == 0x44,
                "bits: %02x %02x %02x %02x\n", bits[0], bits[1], bits[2], bits[3]);
         else if (is_alpha)
@@ -195,7 +194,6 @@ static void test_image(HBITMAP image, BOOL is_dib, BOOL is_premult, BOOL is_alph
     DeleteDC(hdc);
 
     if (is_premult)
-        todo_wine
         ok(bits[0] == 0x05 &&  bits[1] == 0x09 &&  bits[2] == 0x0e && bits[3] == 0x44,
            "bits: %02x %02x %02x %02x\n", bits[0], bits[1], bits[2], bits[3]);
     else if (is_alpha)