Switch to premultiplied space inside Agg for RGBA blending

ayshih · ayshih · commit dd24e05a30cf · 2026-03-01T21:57:55.000-05:00
Premultiplied image data is passed to the Agg resampler so that the
interpolation is handled correctly.  This code now tells Agg that the
image is premultiplied so that the antialiasing of edges is handled
correctly.
diff --git a/src/_image_resample.h b/src/_image_resample.h
@@ -511,7 +511,7 @@ struct type_mapping
         std::conditional_t<
             std::is_same_v<color_type, agg::rgba8>,
             fixed_blender_rgba_plain<color_type, agg::order_rgba>,
-            agg::blender_rgba_plain<color_type, agg::order_rgba>
+            agg::blender_rgba_pre<color_type, agg::order_rgba>
         >
     >;
     using pixfmt_type = std::conditional_t<

Original file line number	Diff line number	Diff line change
`@@ -511,7 +511,7 @@ struct type_mapping`
`511`	`511`	`std::conditional_t<`
`512`	`512`	`std::is_same_v<color_type, agg::rgba8>,`
`513`	`513`	`fixed_blender_rgba_plain<color_type, agg::order_rgba>,`
`514`		`- agg::blender_rgba_plain<color_type, agg::order_rgba>`
	`514`	`+ agg::blender_rgba_pre<color_type, agg::order_rgba>`
`515`	`515`	`>`
`516`	`516`	`>;`
`517`	`517`	`using pixfmt_type = std::conditional_t<`