Current status of EGL spec
brian.paul at tungstengraphics.com
Thu Aug 11 08:26:29 EST 2005
Adam Jackson wrote:
> On Wednesday 10 August 2005 14:49, Michel Danzer wrote:
>>On Wed, 2005-08-10 at 08:17 -0600, Brian Paul wrote:
>>>First, OpenGL conventionally doesn't use in/out parameters like that.
>>> Second, how common is it that hardware can't support 1-pixel
>>>positioning? If it's not a common problem, I'd defer for a future
>>>extension which would allow you to query the positioning granularity.
>>As mentioned by Jon, our current hardware can only position the CRTC
>>offset with a granularity of 8 bytes (i.e. 2-8 horizontal pixels).
>>Upcoming hardware will only support horizontal panning with a
>>granularity of four pixels (irrespective of depth).
> ISTR a few cards that can only change the viewport within the granularity of a
> single framebuffer tile. I believe savage works this way at least.
> How about this: eglScreenPositionMESA snaps to the northwest if the requested
> position isn't aligned, and add EGL_SCREEN_STEP_[XY] to eglQueryScreenMESA,
> which return the grid intervals in pixel units.
I'd call the query EGL_SCREEN_POSITION_GRANULARITY_MESA (returning two
values). The granularity term comes from the queries for point size
and line width.
If there's no objections, I could add that to the spec.
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