gdiplus: Prefer using pre-multiplied ARGB data in the scaler.

dlls/gdiplus/graphics.c

@@ -600,6 +600,17 @@ static GpStatus alpha_blend_pixels(GpGraphics *graphics, INT dst_x, INT dst_y,
     return alpha_blend_pixels_hrgn(graphics, dst_x, dst_y, src, src_width, src_height, src_stride, NULL, fmt);
 }
 
+/* NOTE: start and end pixels must be in pre-multiplied ARGB format */
+static FORCEINLINE ARGB blend_colors_premult(ARGB start, ARGB end, REAL position)
+{
+    UINT pos = position * 255.0f + 0.5f;
+    return
+        (((((start >> 24)       ) << 8) + (((end >> 24)       ) - ((start >> 24)       )) * pos) >> 8) << 24 |
+        (((((start >> 16) & 0xff) << 8) + (((end >> 16) & 0xff) - ((start >> 16) & 0xff)) * pos) >> 8) << 16 |
+        (((((start >>  8) & 0xff) << 8) + (((end >>  8) & 0xff) - ((start >>  8) & 0xff)) * pos) >> 8) <<  8 |
+        (((((start      ) & 0xff) << 8) + (((end      ) & 0xff) - ((start      ) & 0xff)) * pos) >> 8);
+}
+
 static ARGB blend_colors(ARGB start, ARGB end, REAL position)
 {
     INT start_a, end_a, final_a;
@@ -1085,6 +1096,75 @@ static ARGB resample_bitmap_pixel(GDIPCONST GpRect *src_rect, LPBYTE bits, UINT
     }
 }
 
+static ARGB resample_bitmap_pixel_premult(GDIPCONST GpRect *src_rect, LPBYTE bits, UINT width,
+    UINT height, GpPointF *point, GDIPCONST GpImageAttributes *attributes,
+    InterpolationMode interpolation, PixelOffsetMode offset_mode)
+{
+    static int fixme;
+
+    switch (interpolation)
+    {
+    default:
+        if (!fixme++)
+            FIXME("Unimplemented interpolation %i\n", interpolation);
+        /* fall-through */
+    case InterpolationModeBilinear:
+    {
+        REAL leftxf, topyf;
+        INT leftx, rightx, topy, bottomy;
+        ARGB topleft, topright, bottomleft, bottomright;
+        ARGB top, bottom;
+        float x_offset;
+
+        leftx = (INT)point->X;
+        leftxf = (REAL)leftx;
+        rightx = positive_ceilf(point->X);
+        topy = (INT)point->Y;
+        topyf = (REAL)topy;
+        bottomy = positive_ceilf(point->Y);
+
+        if (leftx == rightx && topy == bottomy)
+            return sample_bitmap_pixel(src_rect, bits, width, height,
+                leftx, topy, attributes);
+
+        topleft = sample_bitmap_pixel(src_rect, bits, width, height,
+            leftx, topy, attributes);
+        topright = sample_bitmap_pixel(src_rect, bits, width, height,
+            rightx, topy, attributes);
+        bottomleft = sample_bitmap_pixel(src_rect, bits, width, height,
+            leftx, bottomy, attributes);
+        bottomright = sample_bitmap_pixel(src_rect, bits, width, height,
+            rightx, bottomy, attributes);
+
+        x_offset = point->X - leftxf;
+        top = blend_colors_premult(topleft, topright, x_offset);
+        bottom = blend_colors_premult(bottomleft, bottomright, x_offset);
+
+        return blend_colors_premult(top, bottom, point->Y - topyf);
+    }
+    case InterpolationModeNearestNeighbor:
+    {
+        FLOAT pixel_offset;
+        switch (offset_mode)
+        {
+        default:
+        case PixelOffsetModeNone:
+        case PixelOffsetModeHighSpeed:
+            pixel_offset = 0.5;
+            break;
+
+        case PixelOffsetModeHalf:
+        case PixelOffsetModeHighQuality:
+            pixel_offset = 0.0;
+            break;
+        }
+        return sample_bitmap_pixel(src_rect, bits, width, height,
+            floorf(point->X + pixel_offset), point->Y + pixel_offset, attributes);
+    }
+
+    }
+}
+
 static REAL intersect_line_scanline(const GpPointF *p1, const GpPointF *p2, REAL y)
 {
     return (p1->X - p2->X) * (p2->Y - y) / (p2->Y - p1->Y) + p2->X;
@@ -3234,8 +3314,10 @@ GpStatus WINGDIPAPI GdipDrawImagePointsRect(GpGraphics *graphics, GpImage *image
             lockeddata.Scan0 = src_data;
             if (!do_resampling && bitmap->format == PixelFormat32bppPARGB)
                 lockeddata.PixelFormat = apply_image_attributes(imageAttributes, NULL, 0, 0, 0, ColorAdjustTypeBitmap, bitmap->format);
-            else
+            else if (imageAttributes != &defaultImageAttributes)
                 lockeddata.PixelFormat = PixelFormat32bppARGB;
+            else
+                lockeddata.PixelFormat = PixelFormat32bppPARGB;
 
             stat = GdipBitmapLockBits(bitmap, &src_area, ImageLockModeRead|ImageLockModeUserInputBuf,
                 lockeddata.PixelFormat, &lockeddata);
@@ -3293,8 +3375,14 @@ GpStatus WINGDIPAPI GdipDrawImagePointsRect(GpGraphics *graphics, GpImage *image
                         dst_color = (ARGB*)(dst_data + dst_stride * (y - dst_area.top) + sizeof(ARGB) * (x - dst_area.left));
 
                         if (src_pointf.X >= srcx && src_pointf.X < srcx + srcwidth && src_pointf.Y >= srcy && src_pointf.Y < srcy+srcheight)
-                            *dst_color = resample_bitmap_pixel(&src_area, src_data, bitmap->width, bitmap->height, &src_pointf,
-                                                               imageAttributes, interpolation, offset_mode);
+                        {
+                            if (lockeddata.PixelFormat != PixelFormat32bppPARGB)
+                                *dst_color = resample_bitmap_pixel(&src_area, src_data, bitmap->width, bitmap->height, &src_pointf,
+                                                                   imageAttributes, interpolation, offset_mode);
+                            else
+                                *dst_color = resample_bitmap_pixel_premult(&src_area, src_data, bitmap->width, bitmap->height, &src_pointf,
+                                                                           imageAttributes, interpolation, offset_mode);
+                        }
                         else
                             *dst_color = 0;