From 7aacae170f7711548141b0b9676d53f8b7357545 Mon Sep 17 00:00:00 2001
From: Hermet Park <hermet@lottiefiles.com>
Date: Thu, 12 Sep 2024 19:12:26 +0900
Subject: [PATCH] sw_engine: rectified 8 grayscale drawing

8 bits matting images must be blended, not overwriting.

issue: https://github.com/thorvg/thorvg/issues/1767
---
 src/renderer/sw_engine/tvgSwRaster.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/renderer/sw_engine/tvgSwRaster.cpp b/src/renderer/sw_engine/tvgSwRaster.cpp
index 8e689811..5d5f066c 100644
--- a/src/renderer/sw_engine/tvgSwRaster.cpp
+++ b/src/renderer/sw_engine/tvgSwRaster.cpp
@@ -1338,11 +1338,13 @@ static bool _rasterDirectMattedImage(SwSurface* surface, const SwImage* image, c
             auto src = sbuffer;
             if (opacity == 255) {
                 for (uint32_t x = 0; x < w; ++x, ++dst, ++src, cmp += csize) {
-                    *dst = MULTIPLY(A(*src), alpha(cmp));
+                    auto tmp = MULTIPLY(A(*src), alpha(cmp));
+                    *dst = tmp + MULTIPLY(*dst, 255 - tmp);
                 }
             } else {
                 for (uint32_t x = 0; x < w; ++x, ++dst, ++src, cmp += csize) {
-                    *dst = MULTIPLY(A(*src), MULTIPLY(opacity, alpha(cmp)));
+                    auto tmp = MULTIPLY(A(*src), MULTIPLY(opacity, alpha(cmp)));
+                    *dst = tmp + MULTIPLY(*dst, 255 - tmp);
                 }
             }
             buffer += surface->stride;