[PATCH 0/1] MR8938: gdiplus: Manually blend to white background if the device doesn't support alpha blending.

[PATCH 1/1] gdiplus: Manually blend to white background if the device doesn't support alpha blending.

[Dmitry Timoshkov]

From: Dmitry Timoshkov

Signed-off-by: Dmitry Timoshkov 
---
 dlls/gdiplus/graphics.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/dlls/gdiplus/graphics.c b/dlls/gdiplus/graphics.c
index 700914e6f6e..2a053a80408 100644
--- a/dlls/gdiplus/graphics.c
+++ b/dlls/gdiplus/graphics.c
@@ -550,6 +550,27 @@ static GpStatus alpha_blend_bmp_pixels(GpGraphics *graphics, INT dst_x, INT dst_
     return Ok;
 }

+static void blend_32bppARGB(UINT width, UINT height, BYTE *dst_bits,
+    INT dst_stride, const BYTE *src_bits, INT src_stride)
+{
+    INT x, y;
+    for (y = 0; y < height; y++)
+    {
+        const BYTE *src = src_bits + y * src_stride;
+        BYTE *dst = dst_bits + y * dst_stride;
+        for (x = 0; x < width; x++)
+        {
+            BYTE alpha = src[3];
+            /* blend to white background */
+            *dst++ = (*src++ * alpha + 127) / 255 + (255 - alpha);
+            *dst++ = (*src++ * alpha + 127) / 255 + (255 - alpha);
+            *dst++ = (*src++ * alpha + 127) / 255 + (255 - alpha);
+            *dst++ = 255;
+            src++;
+        }
+    }
+}
+
 static GpStatus alpha_blend_hdc_pixels(GpGraphics *graphics, INT dst_x, INT dst_y,
     const BYTE *src, INT src_width, INT src_height, INT src_stride, PixelFormat fmt)
 {
@@ -582,7 +603,8 @@ static GpStatus alpha_blend_hdc_pixels(GpGraphics *graphics, INT dst_x, INT dst_
          GetDeviceCaps(graphics->hdc, TECHNOLOGY) == DT_RASPRINTER &&
          GetDeviceCaps(graphics->hdc, SHADEBLENDCAPS) == SB_NONE) ||
             fmt & PixelFormatPAlpha)
-        memcpy(temp_bits, src, src_width * src_height * 4);
+        blend_32bppARGB(src_width, src_height, temp_bits,
+                        4 * src_width, src, src_stride);
     else
         convert_32bppARGB_to_32bppPARGB(src_width, src_height, temp_bits,
                                         4 * src_width, src, src_stride);

[Dmitry Timoshkov (＠dmitry)]

[gdip_print.tar.bz2](/uploads/f1b7ace82f2dcec9407610a5108a0e0b/gdip_print.tar.bz2) is a sample application that could be used for testing.

[Dmitry Timoshkov (＠dmitry)]

![img_9x9_32bpp(3).png](/uploads/f169363798ef9ac96be0263e9e6f7867/img_9x9_32bpp_3_.png){width=6 height=6} is an actual image that is being printed. It's a 32bpp ARGB PNG that contains only an alpha channel (a mask), and it's currently printed as a black square because alpha is completely ignored for a printer device.

[PATCH 0/1] MR8938: gdiplus: Manually blend to white background if the device doesn't support alpha blending. - approved

[Esme Povirk (＠madewokherd)]

This merge request was approved by Esme Povirk.