[Mesa-dev] [PATCH v2] main/buffers: update error handling on DrawBuffers for 4.5

[Anuj Phogat]

On Wed, Jan 11, 2017 at 2:00 PM, Alejandro Piñeiro <apinheiro at igalia.com> wrote:
> Before 4.5, GL_BACK was not allowed as a value of bufs. Since 4.5 it
> is allowed under some circunstances:
>
> From the OpenGL 4.5 specification, Section 17.4.1 "Selecting Buffers
> for Writing", page 493 (page 515 of the PDF):
>  "An INVALID_ENUM error is generated if any value in bufs is FRONT ,
>   LEFT , RIGHT , or FRONT_AND_BACK . This restriction applies to both
>   the de- fault framebuffer and framebuffer objects, and exists
>   because these constants may themselves refer to multiple buffers, as
>   shown in table 17.4."
>
> And on page 492 (page 514 of the PDF):
>  "If the default framebuffer is affected, then each of the constants
>   must be one of the values listed in table 17.6 or the special value
>   BACK . When BACK is used, n must be 1 and color values are written
>   into the left buffer for single-buffered contexts, or into the back
>   left buffer for double-buffered contexts."
>
> This patch keeps the same behaviour if OpenGL version is < 4. We
> assume that for 4.x this is the intended behaviour, so a fix, but for
> 3.x the intended behaviour is the already in place.
>
> Part of the fix for:
> GL45-CTS.direct_state_access.framebuffers_draw_read_buffers_errors
>
> v2: remove forgot printf
> ---
>
> Previous version has a debug printf that I forgot to remove. Sorry for
> the noise.
>
>  src/mesa/main/buffers.c | 46 +++++++++++++++++++++++++++++++++-------------
>  1 file changed, 33 insertions(+), 13 deletions(-)
>
> diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
> index 2b24e5a..46ba4fd 100644
> --- a/src/mesa/main/buffers.c
> +++ b/src/mesa/main/buffers.c
> @@ -343,7 +343,9 @@ _mesa_NamedFramebufferDrawBuffer(GLuint framebuffer, GLenum buf)
>   * \param n  number of outputs
>   * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
>   *                 names cannot specify more than one buffer.  For example,
> - *                 GL_FRONT_AND_BACK is illegal.
> + *                 GL_FRONT_AND_BACK is illegal. The only exception is GL_BACK
> + *                 that is considered special and allowed as far as n is one
> + *                 since 4.5.
>   */
>  static void
>  draw_buffers(struct gl_context *ctx, struct gl_framebuffer *fb,
> @@ -401,20 +403,38 @@ draw_buffers(struct gl_context *ctx, struct gl_framebuffer *fb,
>           return;
>        }
>
> -      /* From the OpenGL 4.0 specification, page 256:
> -       * "For both the default framebuffer and framebuffer objects, the
> -       *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
> -       *  valid in the bufs array passed to DrawBuffers, and will result in
> -       *  the error INVALID_ENUM. This restriction is because these
> -       *  constants may themselves refer to multiple buffers, as shown in
> -       *  table 4.4."
> -       *  Previous versions of the OpenGL specification say INVALID_OPERATION,
> -       *  but the Khronos conformance tests expect INVALID_ENUM.
> +      /* From the OpenGL 4.5 specification, page 493 (page 515 of the PDF)
> +       * "An INVALID_ENUM error is generated if any value in bufs is FRONT
> +       *  , LEFT , RIGHT , or FRONT_AND_BACK . This restriction applies to
Need no space before comma. Move it after the comma.
> +       *  both the de- fault framebuffer and framebuffer objects, and
> +       *  exists because these constants may themselves refer to multiple
> +       *  buffers, as shown in table 17.4."
> +       *
> +       * And on page 492 (page 514 of the PDF):
> +       * "If the default framebuffer is affected, then each of the
> +       *  constants must be one of the values listed in table 17.6 or the
> +       *  special value BACK . When BACK is used, n must be 1 and color
> +       *  values are written into the left buffer for single-buffered
> +       *  contexts, or into the back left buffer for double-buffered
> +       *  contexts."
> +       *
> +       * Note "special value BACK". GL_BACK also refers to multiple buffers,
> +       * but it is consider a special case here. This is a change on 4.5. For
> +       * OpenGL 4.x we check that behaviour. For any previous version we keep
> +       * considering it wrong (as INVALID_ENUM).
>         */
>        if (_mesa_bitcount(destMask[output]) > 1) {
> -         _mesa_error(ctx, GL_INVALID_ENUM, "%s(invalid buffer %s)",
> -                     caller, _mesa_enum_to_string(buffers[output]));
> -         return;
> +         if (_mesa_is_winsys_fbo(fb) && ctx->Version >= 40 && buffers[output] == GL_BACK) {
Split in two lines. Exceeding the 80 character limit.
> +            if (n != 1) {
> +               _mesa_error(ctx, GL_INVALID_OPERATION, "%s(with GL_BACK n must be 1)",
> +                           caller);
> +               return;
> +            }
> +         } else {
> +            _mesa_error(ctx, GL_INVALID_ENUM, "%s(invalid buffer %s)",
> +                        caller, _mesa_enum_to_string(buffers[output]));
> +            return;
> +         }
>        }
>
>        /* Section 4.2 (Whole Framebuffer Operations) of the OpenGL ES 3.0
> --
> 2.9.3
>
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With above comments fixed, both patches are:
Reviewed-by: Anuj Phogat <anuj.phogat at gmail.com>