On Thu, 3 Jun 2010 13:24:08 -0400, Kristian Høgsberg <k...@bitplanet.net> wrote: > On Thu, Jun 3, 2010 at 1:16 PM, Brian Paul <bri...@vmware.com> wrote: > > Jakob Bornecrantz wrote: > >> > >> Currently these extensions try to address two use cases. Creating > >> Images to be shared between processes. Creating resources to be used > >> as a scanout target. Leaving the sharing aside until later. Lets look > >> at some of the problems associated with that. > >> > >> Resources suitable for scanout can be used as a render target and as a > >> sampling source. So renderbuffer and/or texture is a good > >> representation of it, it is also how we want to operate on it, but > >> they are both GL objects. A EGL image however can be both of these > >> objects and more and is far more flexible then a EGL surface. So lets > >> use EGL image as the sharing object. > >> > >> The problem is that we just can't go from a any texture that happens > >> to be large enough to a scanout buffer. Most hardware have stricter > >> limitations on stride, tiling, placement, etc on scanout buffers then > >> textures/rendertargets or those limitation make certain uses slower or > >> use more memory compared to normal textures/renderbuffers. So we can't > >> just go around creating all texture and renderbuffer as suitable for > >> scanout just because sometime we might use it as a scanout, because it > >> would be slower and use more memory. Now we don't have a way to say a > >> texture/renderbuffer should be scanoutable in GL. And creating a EGL > >> image from a texture/rendertarget and then mutating it into a > >> scanoutable format is bad, it would effectively orphan the original > >> resource unless we do major hacking in the driver which I don't want > >> to do. Enter MESA_create_image and MESA_image_syste_use to solve this > >> problem. Ok now we have a EGL image that can be used as a scanout and > >> be shared to all the API's we want to use to render to it. > > > > > > What's the use-case for a scanout buffer that's used as a texture? That > > seems like an unusual case. > > You could be pageflipping between two scanout EGLImages. If you're > only rendering partial updates (using EGL_NOK_swap_region, for > example) you want to copy the updated region back from the scanout > buffer to the new backbuffer before rendering the next frame.
Also, implementing an X Server on GL without the scanout buffer being a texture means either I can't accelerate a lot of operations that should be fast, like background none composited window initialization, or I have to keep a shadow texture and periodically update front.
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