[PATCH 1/2] drm/vkms: Use alpha for blending in blend() function

[Rodrigo Siqueira]

Hi,

I tested your patch with kms_cursor_crc, and everything worked as
expected! Really nice patch :)

I just have some tiny comments inline.

On 01/24, Mamta Shukla wrote:
> Use the alpha value to blend vaddr_src with vaddr_dst instead
> of overwriting it in blend().
> 
> Signed-off-by: Mamta Shukla <mamtashukla555 at gmail.com>
> ---
>  drivers/gpu/drm/vkms/vkms_crc.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> index 9d9e8146db90..13d5ffed9135 100644
> --- a/drivers/gpu/drm/vkms/vkms_crc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> @@ -70,7 +70,8 @@ static void blend(void *vaddr_dst, void *vaddr_src,
>  
>  	int y_limit = y_src + h_dst;
>  	int x_limit = x_src + w_dst;
> -
> +	u8 alpha, r_src, r_dst, g_src, g_dst, b_src, b_dst;
> +	u8 r_alpha, g_alpha, b_alpha;
>  	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 = crc_dst->offset
> @@ -80,8 +81,23 @@ static void blend(void *vaddr_dst, void *vaddr_src,
>  				     + (i * crc_src->pitch)
>  				     + (j * crc_src->cpp);
>  
> -			memcpy(vaddr_dst + offset_dst,
> -			       vaddr_src + offset_src, sizeof(u32));
> +			/*Currently handles alpha values for fully opaque or fully transparent */
> +			alpha = (u8)((*(u32 *)(vaddr_src + offset_src)) >> 24);
> +			alpha = alpha/255;

Add spaces between '/'.

> +			r_src = (u8)((*(u32 *)(vaddr_src + offset_src)) >> 16 & 0xff);
> +			g_src = (u8)((*(u32 *)(vaddr_src + offset_src)) >> 8  & 0xff);
> +			b_src = (u8)((*(u32 *)(vaddr_src + offset_src)) & 0xff);
> +			r_dst = (u8)((*(u32 *)(vaddr_dst + offset_dst)) >> 16 & 0xff);
> +			g_dst = (u8)((*(u32 *)(vaddr_dst + offset_dst)) >> 8 & 0xff);
> +			b_dst = (u8)((*(u32 *)(vaddr_dst + offset_dst)) & 0xff);

Since these operations are very similar, it could be better to create
one inline function or macro to reduce the code duplication. I'm not
sure, but I suspect that Linux already provides some macros for this
sort of operations (again, I'm not sure).

> +
> +			/*Pre-multiplied alpha for blending */
> +			r_alpha = (r_src) + (r_dst * (1 -alpha));
> +			g_alpha = (g_src) + (g_dst * (1 -alpha));
> +			b_alpha = (b_src) + (b_dst * (1 -alpha));

Add space between '-'.

> +			memset(vaddr_dst + offset_dst, b_alpha, sizeof(u8));
> +			memset(vaddr_dst + offset_dst + 1, g_alpha, sizeof(u8));			

Take care with extra spaces at the end.

Finally, remember to run checkpatch in your patches.

> +			memset(vaddr_dst + offset_dst + 2, r_alpha, sizeof(u8));
>  		}
>  		i_dst++;
>  	}
> -- 
> 2.17.1
> 

-- 
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of São Paulo