The VKMS blend function was ignoring the alpha channel and just
overwriting vaddr_src with vaddr_dst. This XRGB approach triggers a
warning when running the kms_cursor_crc/cursor-alpha-transparent test
case. In IGT, cairo_format_argb32 uses premultiplied alpha (according to
documentation). Also current DRM assumption is that alpha is
premultiplied. Therefore, this patch considers premultiplied alpha
blending eq to compose vaddr_src with vaddr_dst.
This change removes the following cursor-alpha-transparent warning:
"Suspicious CRC: All values are 0."
--
v2:
- static for local functions
- const for the read-only variable argb_src
- replaces variable names
- drops unnecessary comment
--
Cc: Daniel Vetter <dan...@ffwll.ch>
Cc: Rodrigo Siqueira <rodrigosiqueiram...@gmail.com>
Cc: Haneen Mohammed <hamohammed...@gmail.com>
Signed-off-by: Melissa Wen <melissa....@gmail.com>
---
drivers/gpu/drm/vkms/vkms_composer.c | 55 ++++++++++++++++++++--------
1 file changed, 39 insertions(+), 16 deletions(-)
diff --git a/drivers/gpu/drm/vkms/vkms_composer.c
b/drivers/gpu/drm/vkms/vkms_composer.c
index 4f3b07a32b60..eaecc5a6c5db 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -32,8 +32,6 @@ static uint32_t compute_crc(void *vaddr_out, struct
vkms_composer *composer)
src_offset = composer->offset
+ (i * composer->pitch)
+ (j * composer->cpp);
- /* XRGB format ignores Alpha channel */
- bitmap_clear(vaddr_out + src_offset, 24, 8);
crc = crc32_le(crc, vaddr_out + src_offset,
sizeof(u32));
}
@@ -42,27 +40,51 @@ static uint32_t compute_crc(void *vaddr_out, struct
vkms_composer *composer)
return crc;
}
+static u8 blend_channel(u8 src, u8 dst, u8 alpha)
+{
+ u32 pre_blend;
+ u8 new_color;
+
+ pre_blend = (src * 255 + dst * (255 - alpha));
+
+ /* Faster div by 255 */
+ new_color = ((pre_blend + ((pre_blend + 257) >> 8)) >> 8);
+
+ return new_color;
+}
+
+static void alpha_blending(const u8 *argb_src, u8 *argb_dst)
+{
+ u8 alpha;
+
+ alpha = argb_src[3];
+ argb_dst[0] = blend_channel(argb_src[0], argb_dst[0], alpha);
+ argb_dst[1] = blend_channel(argb_src[1], argb_dst[1], alpha);
+ argb_dst[2] = blend_channel(argb_src[2], argb_dst[2], alpha);
+ /* Opaque primary */
+ argb_dst[3] = 0xFF;
+}
+
/**
* blend - blend value at vaddr_src with value at vaddr_dst
* @vaddr_dst: destination address
* @vaddr_src: source address
- * @dest_composer: destination framebuffer's metadata
+ * @dst_composer: destination framebuffer's metadata
* @src_composer: source framebuffer's metadata
*
- * Blend value at vaddr_src with value at vaddr_dst.
- * Currently, this function write value of vaddr_src on value
- * at vaddr_dst using buffer's metadata to locate the new values
- * from vaddr_src and their destination at vaddr_dst.
- *
- * TODO: Use the alpha value to blend vaddr_src with vaddr_dst
- * instead of overwriting it.
+ * Blend the vaddr_src value with the vaddr_dst value using the pre-multiplied
+ * alpha blending equation, since DRM currently assumes that the pixel color
+ * values have already been pre-multiplied with the alpha channel values. See
+ * more drm_plane_create_blend_mode_property(). This function uses buffer's
+ * metadata to locate the new composite values at vaddr_dst.
*/
static void blend(void *vaddr_dst, void *vaddr_src,
- struct vkms_composer *dest_composer,
+ struct vkms_composer *dst_composer,
struct vkms_composer *src_composer)
{
int i, j, j_dst, i_dst;
int offset_src, offset_dst;
+ u8 *pixel_dst, *pixel_src;
int x_src = src_composer->src.x1 >> 16;
int y_src = src_composer->src.y1 >> 16;
@@ -77,15 +99,16 @@ 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) {
- offset_dst = dest_composer->offset
- + (i_dst * dest_composer->pitch)
- + (j_dst++ * dest_composer->cpp);
+ offset_dst = dst_composer->offset
+ + (i_dst * dst_composer->pitch)
+ + (j_dst++ * dst_composer->cpp);
offset_src = src_composer->offset
+ (i * src_composer->pitch)
+ (j * src_composer->cpp);
- memcpy(vaddr_dst + offset_dst,
- vaddr_src + offset_src, sizeof(u32));
+ pixel_src = (u8 *)(vaddr_src + offset_src);
+ pixel_dst = (u8 *)(vaddr_dst + offset_dst);
+ alpha_blending(pixel_src, pixel_dst);
}
i_dst++;
}
--
2.28.0
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