The current VKMS blend function ignores alpha channel and just overwrites
vaddr_src with vaddr_dst. This XRGB approach triggers a warning when
running the kms_cursor_crc/cursor-alpha-transparent test case. In IGT
tests, cairo_format_argb32 uses premultiplied alpha (according to
documentation), so this patch considers premultiplied alpha colors to
compose vaddr_src with vaddr_dst.
This change removes the following cursor-alpha-transparent warning:
Suspicious CRC: All values are 0.
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 | 43 +++++++++++++++++++++-------
1 file changed, 33 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/vkms/vkms_composer.c
b/drivers/gpu/drm/vkms/vkms_composer.c
index 4f3b07a32b60..6aac962d3e2e 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));
}
@@ -42,6 +40,32 @@ static uint32_t compute_crc(void *vaddr_out, struct
vkms_composer *composer)
return crc;
}
+u8 blend_channel(u8 c_src, u8 c_dst, u8 a_src)
+{
+ u32 pre_blend;
+ u8 new_color;
+
+ /* Premultiplied alpha blending - IGT + cairo context */
+ pre_blend = (c_src * 255 + c_dst * (255 - a_src));
+
+ /* Faster div by 255 */
+ new_color = ((pre_blend + ((pre_blend + 257) >> 8)) >> 8);
+
+ return new_color;
+}
+
+void alpha_blending(u8 *argb_src, u8 *argb_dst)
+{
+ u8 a_src;
+
+ a_src = argb_src[3];
+ argb_dst[0] = blend_channel(argb_src[0], argb_dst[0], a_src);
+ argb_dst[1] = blend_channel(argb_src[1], argb_dst[1], a_src);
+ argb_dst[2] = blend_channel(argb_src[2], argb_dst[2], a_src);
+ /* Opaque primary */
+ argb_dst[3] = 0xFF;
+}
+
/**
* blend - blend value at vaddr_src with value at vaddr_dst
* @vaddr_dst: destination address
@@ -50,12 +74,9 @@ static uint32_t compute_crc(void *vaddr_out, struct
vkms_composer *composer)
* @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.
+ * Currently, this function considers premultiplied alpha for blending, as used
+ * by Cairo. It 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,
@@ -63,6 +84,7 @@ static void blend(void *vaddr_dst, void *vaddr_src,
{
int i, j, j_dst, i_dst;
int offset_src, offset_dst;
+ u8 *p_dst, *p_src;
int x_src = src_composer->src.x1 >> 16;
int y_src = src_composer->src.y1 >> 16;
@@ -84,8 +106,9 @@ 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));
+ p_src = (u8 *)(vaddr_src + offset_src);
+ p_dst = (u8 *)(vaddr_dst + offset_dst);
+ alpha_blending(p_src, p_dst);
}
i_dst++;
}
--
2.28.0
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