[Mesa-dev] [PATCH] swrast: fix readpix clamping

[Ian Romanick]

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On 04/20/2011 03:57 AM, Marek Olšák wrote:
> Broken with e5c6a92a12b5cd7db205d72039f58d302b0be9d5. (ARB_color_buffer_float)
> 
> Clamping should occur if type != float, otherwise the MSBs of the resulting
> pixels are killed off. For example, reading back LUMIMANCE = R+G+B can be
> greater than 0xff, but the result is naturally masked by 0xff
> for UNSIGNED_BYTE, leading to bogus results.
> 
> The following bug report seems to want clamping to occur if type == half_float
> too. Not sure what's correct.
> 
> Bug: [bisected pineview] oglc case pxconv-read failed
> https://bugs.freedesktop.org/show_bug.cgi?id=35852

Reviewed-and-tested-by: Ian Romanick <ian.d.romanick at intel.com>

> ---
>  src/mesa/swrast/s_readpix.c |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/src/mesa/swrast/s_readpix.c b/src/mesa/swrast/s_readpix.c
> index 5604c2e..9e0f0d5 100644
> --- a/src/mesa/swrast/s_readpix.c
> +++ b/src/mesa/swrast/s_readpix.c
> @@ -315,12 +315,12 @@ read_rgba_pixels( struct gl_context *ctx,
>     if (!rb)
>        return;
>  
> -   if (type == GL_FLOAT && ((ctx->Color.ClampReadColor == GL_TRUE) ||
> -                            (ctx->Color.ClampReadColor == GL_FIXED_ONLY_ARB &&
> -                             rb->DataType != GL_FLOAT)))
> +   if ((ctx->Color._ClampReadColor == GL_TRUE || type != GL_FLOAT) &&
> +       !_mesa_is_integer_format(format)) {
>        transferOps |= IMAGE_CLAMP_BIT;
> +   }
>  
> -   /* Try optimized path first */
> +   /* Try the optimized path first. */
>     if (fast_read_rgba_pixels(ctx, x, y, width, height,
>                               format, type, pixels, packing, transferOps)) {
>        return; /* done! */

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