Re: [PATCH v2] drm/vkms: add alpha-premultiplied color blending

Reviewed-by: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com

On 08/25, Melissa Wen wrote:

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

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