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drm/vkms: add alpha-premultiplied color blending

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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 <daniel@ffwll.ch>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200825114532.abzdooluny2ekzvm@smtp.gmail.com
This commit is contained in:
Melissa Wen 2020-08-25 08:45:32 -03:00 committed by Rodrigo Siqueira
parent 3b80951699
commit 39cba5cf8c
1 changed files with 39 additions and 16 deletions
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55
drivers/gpu/drm/vkms/vkms_composer.c
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@ -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++;
}