Messages in this thread | | | Date | Mon, 24 Aug 2020 23:04:04 -0400 | From | Rodrigo Siqueira <> | Subject | Re: [PATCH] drm/vkms: add alpha-premultiplied color blending |
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Hi Melissa,
First of all, thanks a lot for your patch!
Follows my inline comments.
On 08/19, Melissa Wen wrote: > 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 <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 | 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)
Use static here.
Also, replace c_src to src, c_dst to dst, and a_src to alpha.
> +{ > + u32 pre_blend; > + u8 new_color; > + > + /* Premultiplied alpha blending - IGT + cairo context */
You can drop the part that says "IGT + cairo context", this explanation better suit the commit message.
> + 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)
Use static.
Looks like that argb_src is a read-only variable, in this sense add const.
> +{ > + u8 a_src; > + > + a_src = argb_src[3];
change a_src to alpha.
> + 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;
I suppose that p stands for "pixel", right? In this case how about use pixel?
Best Regards Rodrigo Siqueira
> > 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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