[Piglit] [PATCH v2] fix read_pixels_float() on GLES2 when format is not GL_RGBA

[Brian Paul]

On 03/28/2018 05:37 AM, Rhys Perry wrote:
> GLES2 requires GL_RGBA to be used with GL_UNSIGNED_BYTE in glReadPixels
> ---
>   tests/util/piglit-util-gl.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tests/util/piglit-util-gl.c b/tests/util/piglit-util-gl.c
> index df39c1c87..0504be063 100644
> --- a/tests/util/piglit-util-gl.c
> +++ b/tests/util/piglit-util-gl.c
> @@ -1029,10 +1029,10 @@ read_pixels_float(GLint x, GLint y, GLsizei width, GLsizei height,
>   		return pixels;
>   	}
>   
> -	pixels_b = malloc(ncomponents * sizeof(GLubyte));
> -	glReadPixels(x, y, width, height, format, GL_UNSIGNED_BYTE, pixels_b);
> +	pixels_b = malloc(width * height * 4 * sizeof(GLubyte));
> +	glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels_b);
>   	for (i = 0; i < ncomponents; i++)
> -		pixels[i] = pixels_b[i] / 255.0;
> +		pixels[i] = pixels_b[i/ncomponents*4+i%ncomponents] / 255.0;

That looks a bit inefficient to me with all the divides and mods, and a 
little hard to follow at first glance.

How about something like this:

int comps = piglit_num_components(format);
int k = 0;
for (i = 0; i < width * height; i++) {
    for (j = 0; j < comps; j++) {
       pixels[k++] = pixels_b[i * 4 + j] / 255.0f;
    }
}

-Brian

>   	free(pixels_b);
>   	return pixels;
>   }
>