On 09/10/2014 01:53 PM, Erik Faye-Lund wrote: > On Tue, Sep 9, 2014 at 7:30 PM, Ian Romanick <i...@freedesktop.org> wrote: >> On 09/08/2014 01:10 AM, Tapani Pälli wrote: >>> From: Kalyan Kondapally <kalyan.kondapa...@intel.com> >>> >>> According to GLSL-ES Spec(i.e. 1.0, 3.0), gl_Position value is undefined >>> after the vertex processing stage if we don't write gl_Position. However, >>> GLSL 1.10 Spec mentions that writing to gl_Position is mandatory. In case >>> of GLSL-ES, it's not an error and atleast the linking should pass. >>> Currently, Mesa throws an linker error in case we dont write to gl_position >>> and Version is less then 140(GLSL) and 300(GLSL-ES). This patch changes >>> it so that we don't report an error in case of GLSL-ES. >> >> Wow. We can add this to the list of ways OpenGL ES is just plain >> broken. > > Historical note: It's not broken, this is by design. The rationale for > why we did this was to ease the burden of compile-time checks for the > compiler - detecting if gl_Position is written no matter how the > program branches is not trivial, so we decided against it. When we > specified this, the typical mobile CPU clock-rate was *a lot* lower > than it is today.
I'd call that broken by design. The overhead of checking that a shader statically accessed a variabl is infinitesimal, no matter how slow your CPU is. These are the sort of cut-corners that make developers hate OpenGL development. "Why is the screen black? No clue." > Sure, it probably could have been fixed for GLES 3.0. I wasn't > involved in those discussions, so I have no insight there. Nope: transform feedback. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
