Saturate alpha values when overlaying glyphs
bug:19062769
Glyphs were stored to the output buffer with the assumption of
non-overlap, which is incorrect for certain fonts/strings. Instead,
blend src into dst, so new glyphs don't clobber existing content.
Change-Id: I6e22037500e67d5348ee2a43d939416c23c4d1ea
diff --git a/libs/hwui/font/Font.cpp b/libs/hwui/font/Font.cpp
index b07a3c8..5de64a4 100644
--- a/libs/hwui/font/Font.cpp
+++ b/libs/hwui/font/Font.cpp
@@ -228,15 +228,15 @@
for (uint32_t cacheY = startY, bitmapY = dstY * bitmapWidth; cacheY < endY;
cacheY += srcStride, bitmapY += bitmapWidth) {
- if (formatSize == 1) {
- memcpy(&bitmap[bitmapY + dstX], &cacheBuffer[cacheY + glyph->mStartX], glyph->mBitmapWidth);
- } else {
- for (uint32_t i = 0; i < glyph->mBitmapWidth; ++i) {
- bitmap[bitmapY + dstX + i] = cacheBuffer[cacheY + (glyph->mStartX + i)*formatSize + alpha_channel_offset];
- }
+ for (uint32_t i = 0; i < glyph->mBitmapWidth; ++i) {
+ uint8_t* dst = &(bitmap[bitmapY + dstX + i]);
+ const uint8_t& src = cacheBuffer[
+ cacheY + (glyph->mStartX + i)*formatSize + alpha_channel_offset];
+ // Add alpha values to a max of 255, full opacity. This is done to handle
+ // fonts/strings where glyphs overlap.
+ *dst = std::min(*dst + src, 255);
}
}
-
}
void Font::drawCachedGlyph(CachedGlyphInfo* glyph, float x, float hOffset, float vOffset,