[PATCH 3/5] gui: fix alpha blend

[Ahmad Fatoum]

On 25.09.24 16:34, Sascha Hauer wrote:
> gu_set_rgba_pixel() can work in two modes. When the plane does have an
> alpha channel then it just sets the RGBA values. When the plane doesn't
> have an alpha channel then it does pseudo alpha blending of the previous
> pixel value.
> 
> At least this was the intention. The function sets the alpha value
> correctly only when it's not fully opaque. Fix this by always setting
> the alpha channel when it exists.
> 
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>

Reviewed-by: Ahmad Fatoum <a.fatoum at pengutronix.de>

> ---
>  lib/gui/graphic_utils.c | 26 ++++++++++++--------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/gui/graphic_utils.c b/lib/gui/graphic_utils.c
> index 93ef1214f9..d9f90f3d2e 100644
> --- a/lib/gui/graphic_utils.c
> +++ b/lib/gui/graphic_utils.c
> @@ -187,24 +187,22 @@ void gu_set_rgba_pixel(struct fb_info *info, void *adr, u8 r, u8 g, u8 b, u8 a)
>  	if (!a)
>  		return;
>  
> -	if (a != 0xff) {
> -		if (info->transp.length) {
> -			px |= (a >> (8 - info->transp.length)) << info->transp.offset;
> -		} else {
> -			u8 sr = 0;
> -			u8 sg = 0;
> -			u8 sb = 0;
> +	if (info->transp.length) {
> +		px |= (a >> (8 - info->transp.length)) << info->transp.offset;
> +	} else if (a != 0xff) {
> +		u8 sr = 0;
> +		u8 sg = 0;
> +		u8 sb = 0;
>  
> -			get_rgb_pixel(info, adr, &sr, &sg, &sb);
> +		get_rgb_pixel(info, adr, &sr, &sg, &sb);
>  
> -			r = alpha_mux(sr, r, a);
> -			g = alpha_mux(sg, g, a);
> -			b = alpha_mux(sb, b, a);
> +		r = alpha_mux(sr, r, a);
> +		g = alpha_mux(sg, g, a);
> +		b = alpha_mux(sb, b, a);
>  
> -			gu_set_rgb_pixel(info, adr, r, g, b);
> +		gu_set_rgb_pixel(info, adr, r, g, b);
>  
> -			return;
> -		}
> +		return;
>  	}
>  
>  	px |= (r >> (8 - info->red.length)) << info->red.offset |
> 


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