Chia-I Wu <olva...@gmail.com> writes: > On Tue, Jan 19, 2010 at 2:40 AM, Brian Paul <bri...@vmware.com> wrote: >>>> But it's not an application bug. >>>> I could write a GL program that never calls glViewport and still draws >>>> something meaningful before/after window resizing. >>> If I understand correctly, the application will draw to an old buffer if >>> a resize happened and it did not call glViewport. Right? >> Are you talking about a specific driver, or in general? >> In general, it depends on how rendering finds its way to the buffer. If >> rendering to a surface goes through some kind of handle, reallocating the >> buffer doesn't change the handle so renering should go to the new buffer. > What I had in mind was all DRI2 drivers. I doubt that the handles point to > the > new buffers automatically, but I am not 100% sure.
Yeah, the handles keep pointing to the old buffers until the X server is asked to allocate the new ones, with DRI2GetBuffers. So, if the glViewport() hack happened to fail for a given application, it would never be able to draw outside the subwindow it originally took up. >>> In that case, we need to call DRI2GetBuffers in buffer swap (for back >>> rendering) or flush frontbuffer (for front rendering), and copy the >>> contents of the old buffer to the new one at a suitable position. >> Off-hand I'm not sure what happens with DRI2. I could try to look later >> when I get some time. Anyone else know? >> >> But in the example I alluded to, my app would detect the resize (probably a >> ConfigureNotify event) and draw a new image and still not call glViewport(). >> Remember that glViewport() _only_ specifies an X/Y transformation of vertex >> coords from NDC to window space. It says nothing about the window size or >> clipping or anything like that. > Yes, this is what I thought what it should be from the application's point of > view. It seems to me that some heuristics are assumed in DRI2 drivers because > of performance concern. I think the DRI2 patches Francisco Jerez sent > yesterday can solve the issue. (CCed Francisco so that he could provide some > insights) Right, that's what I meant to do. > > -olv
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