bmOverwrite nonsimd benchmark

experiments/benchmark_cairo_draw.nim

@@ -72,6 +72,19 @@ block:
 
   # tmp.writeFile("tmp2.png")
 
+block:
+  let
+    backdrop = readImage("tests/fileformats/svg/masters/dragon2.png")
+    source = readImage("tests/fileformats/svg/masters/Ghostscript_Tiger.png")
+    tmp = newImage(1568, 940)
+
+  timeIt "pixie draw overwrite":
+    # tmp.fill(rgbx(127, 127, 127, 255))
+    tmp.draw(backdrop, blendMode = bmOverwrite)
+    tmp.draw(source)
+
+  # tmp.writeFile("tmp2.png")
+
 block:
   let
     backdrop = readImage("tests/fileformats/svg/masters/dragon2.png")

src/pixie/images.nim

@@ -921,13 +921,15 @@ proc drawUber(
               let source = b.unsafe[samplePos.x, samplePos.y]
             else: # b is a Mask
               let source = rgbx(0, 0, 0, b.unsafe[samplePos.x, samplePos.y])
-            a.unsafe[x, y] = source
+            if source.a > 0:
+              a.unsafe[x, y] = source
           else: # a is a Mask
             when type(b) is Image:
               let source = b.unsafe[samplePos.x, samplePos.y].a
             else: # b is a Mask
               let source = b.unsafe[samplePos.x, samplePos.y]
-            a.unsafe[x, y] = source
+            if source > 0:
+              a.unsafe[x, y] = source
           srcPos += dx
       of bmNormal:
         for x in x ..< xMax: