I wrote this patch for TODO list in vkms documentation.
Use alpha value to blend source value and destination value Instead of
just overwrite with source value.
Cc: Rodrigo Siqueira <rodrigosiqueiram...@gmail.com>
Cc: Haneen Mohammed <hamohammed...@gmail.com>
Signed-off-by: Sidong Yang <realwa...@gmail.com>
---
drivers/gpu/drm/vkms/vkms_composer.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/vkms/vkms_composer.c
b/drivers/gpu/drm/vkms/vkms_composer.c
index 4f3b07a32b60..e3230e2a99af 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -77,6 +77,9 @@ static void blend(void *vaddr_dst, void *vaddr_src,
for (i = y_src, i_dst = y_dst; i < y_limit; ++i) {
for (j = x_src, j_dst = x_dst; j < x_limit; ++j) {
+ u8 *src, *dst;
+ u32 alpha, inv_alpha;
+
offset_dst = dest_composer->offset
+ (i_dst * dest_composer->pitch)
+ (j_dst++ * dest_composer->cpp);
@@ -84,8 +87,15 @@ static void blend(void *vaddr_dst, void *vaddr_src,
+ (i * src_composer->pitch)
+ (j * src_composer->cpp);
- memcpy(vaddr_dst + offset_dst,
- vaddr_src + offset_src, sizeof(u32));
+ src = vaddr_src + offset_src;
+ dst = vaddr_dst + offset_dst;
+ alpha = src[3] + 1;
+ inv_alpha = 256 - src[3];
+ dst[0] = (alpha * src[0] + inv_alpha * dst[0]) >> 8;
+ dst[1] = (alpha * src[1] + inv_alpha * dst[1]) >> 8;
+ dst[2] = (alpha * src[2] + inv_alpha * dst[2]) >> 8;
+ dst[3] = 0xff;
+
}
i_dst++;
}
--
2.17.1
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