On Wednesday, June 17, 2015 01:01:15 AM Marek Olšák wrote:
> From: Marek Olšák <marek.ol...@amd.com>
>
> ---
> src/mesa/main/api_validate.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/src/mesa/main/api_validate.c b/src/mesa/main/api_validate.c
> index 401120a..9a5ac69 100644
> --- a/src/mesa/main/api_validate.c
> +++ b/src/mesa/main/api_validate.c
> @@ -69,6 +69,25 @@ check_valid_to_render(struct gl_context *ctx, const char
> *function)
> return false;
> }
>
> + /* The spec argues that this is allowed because a tess ctrl shader
> + * without a tess eval shader can be used with transform feedback.
> + * However, glBeginTransformFeedback doesn't allow GL_PATCHES and
> + * therefore doesn't allow tessellation.
> + *
> + * Further investigation showed that this is indeed a spec bug and
> + * a tess ctrl shader without a tess eval shader shouldn't have been
> + * allowed, because there is no API in GL 4.0 that can make use this
> + * to produce something useful.
> + *
> + * Also, all vendors except one don't support a tess ctrl shader
> without
> + * a tess eval shader anyway.
> + */
> + if (ctx->TessCtrlProgram._Current && !ctx->TessEvalProgram._Current) {
> + _mesa_error(ctx, GL_INVALID_OPERATION,
> + "%s(tess eval shader is missing)", function);
> + return false;
> + }
> +
> /* Section 7.3 (Program Objects) of the OpenGL 4.5 Core Profile spec
> * says:
> *
> This makes sense to me - the TCS always generates patches, and I don't see any way to record those with transform feedback. And nothing else can use patches. So...effectively you need a TES. It sounds like they were leaving the door open for a vendor extension that allowed transform feedback on patches, but nobody has written such an extension yet.
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