Damjan Jovanovic : gdiplus: GdipGraphicsClear() should overwrite pixels, not alpha blend.

[Alexandre Julliard]

Module: wine
Branch: oldstable
Commit: b4e12ea07f033e64a3e236d5f0f796a9e7e40c14
URL:    https://source.winehq.org/git/wine.git/?a=commit;h=b4e12ea07f033e64a3e236d5f0f796a9e7e40c14

Author: Damjan Jovanovic <damjan.jov at gmail.com>
Date:   Fri Dec 13 05:17:54 2019 +0200

gdiplus: GdipGraphicsClear() should overwrite pixels, not alpha blend.

All sample code in the Python Pyglet library suffers from terrible
text corruption, caused by the inability to erase the background
between rendering sequential font glyphs, resulting in leftovers
from previous letters mixing with the image of new letters.

This is because it attempts to erase the background by calling
GdipGraphicsClear() with ARGB color 0x00000000 (completely
transparent black), and in our gdiplus alpha blending that into
the background has no effect. It should be using
CompositeModeSourceCopy to overwrite the background with that brush
instead.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=30506
Signed-off-by: Damjan Jovanovic <damjan.jov at gmail.com>
Signed-off-by: Vincent Povirk <vincent at codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard at winehq.org>
(cherry picked from commit 3c8784bf9c1a897de021587437c5ec4f648c84a1)
Signed-off-by: Michael Stefaniuc <mstefani at winehq.org>

---

 dlls/gdiplus/graphics.c    |  4 ++++
 dlls/gdiplus/tests/image.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/dlls/gdiplus/graphics.c b/dlls/gdiplus/graphics.c
index 3216a3ea43..9ba0b15c77 100644
--- a/dlls/gdiplus/graphics.c
+++ b/dlls/gdiplus/graphics.c
@@ -4942,6 +4942,7 @@ GpStatus WINGDIPAPI GdipGraphicsClear(GpGraphics *graphics, ARGB color)
     GpSolidFill *brush;
     GpStatus stat;
     GpRectF wnd_rect;
+    CompositingMode prev_comp_mode;
 
     TRACE("(%p, %x)\n", graphics, color);
 
@@ -4962,8 +4963,11 @@ GpStatus WINGDIPAPI GdipGraphicsClear(GpGraphics *graphics, ARGB color)
         return stat;
     }
 
+    GdipGetCompositingMode(graphics, &prev_comp_mode);
+    GdipSetCompositingMode(graphics, CompositingModeSourceCopy);
     GdipFillRectangle(graphics, (GpBrush*)brush, wnd_rect.X, wnd_rect.Y,
                                                  wnd_rect.Width, wnd_rect.Height);
+    GdipSetCompositingMode(graphics, prev_comp_mode);
 
     GdipDeleteBrush((GpBrush*)brush);
 
diff --git a/dlls/gdiplus/tests/image.c b/dlls/gdiplus/tests/image.c
index 5aec1c283a..414ef19253 100644
--- a/dlls/gdiplus/tests/image.c
+++ b/dlls/gdiplus/tests/image.c
@@ -5484,6 +5484,48 @@ todo_wine
     GdipDisposeImage((GpImage *)bitmap);
 }
 
+static void test_graphics_clear(void)
+{
+    BYTE argb[8] = { 0x11,0x22,0x33,0x80, 0xff,0xff,0xff,0 };
+    BYTE cleared[8] = { 0,0,0,0, 0,0,0,0 };
+    BYTE *bits;
+    GpBitmap *bitmap;
+    GpGraphics *graphics;
+    BitmapData data;
+    GpStatus status;
+    int match;
+
+    status = GdipCreateBitmapFromScan0(2, 1, 8, PixelFormat32bppARGB, argb, &bitmap);
+    expect(Ok, status);
+
+    status = GdipGetImageGraphicsContext((GpImage*)bitmap, &graphics);
+    expect(Ok, status);
+
+    status = GdipGraphicsClear(graphics, 0x00000000);
+    expect(Ok, status);
+
+    status = GdipBitmapLockBits(bitmap, NULL, ImageLockModeRead, PixelFormat32bppARGB, &data);
+    expect(Ok, status);
+    ok(data.Width == 2, "expected 2, got %d\n", data.Width);
+    ok(data.Height == 1, "expected 1, got %d\n", data.Height);
+    ok(data.Stride == 8, "expected 8, got %d\n", data.Stride);
+    ok(data.PixelFormat == PixelFormat32bppARGB, "expected PixelFormat32bppARGB, got %d\n", data.PixelFormat);
+    match = !memcmp(data.Scan0, cleared, sizeof(cleared));
+    ok(match, "bits don't match\n");
+    if (!match)
+    {
+        bits = data.Scan0;
+        trace("format %#x, bits %02x,%02x,%02x,%02x %02x,%02x,%02x,%02x\n", PixelFormat32bppPARGB,
+               bits[0], bits[1], bits[2], bits[3], bits[4], bits[5], bits[6], bits[7]);
+    }
+    status = GdipBitmapUnlockBits(bitmap, &data);
+    expect(Ok, status);
+
+    status = GdipDeleteGraphics(graphics);
+    expect(Ok, status);
+    GdipDisposeImage((GpImage *)bitmap);
+}
+
 START_TEST(image)
 {
     HMODULE mod = GetModuleHandleA("gdiplus.dll");
@@ -5559,6 +5601,7 @@ START_TEST(image)
     test_histogram();
     test_imageabort();
     test_GdipLoadImageFromStream();
+    test_graphics_clear();
 
     GdiplusShutdown(gdiplusToken);
 }