The index bounds are computed only when they are needed for uploading vertices that are passed via a CPU pointer (user_buffer). In all other cases, computing the index bounds has a performance cost, which can be very significant.
If you rely on u_vbuf to upload vertices for you, you shouldn't need the index bounds. Marek On Sat, Mar 17, 2018 at 2:12 PM, Erico Nunes <nunes.er...@gmail.com> wrote: > Hi all, > > I have been working to add indexed drawing/glDrawElements support to > the mesa-lima driver currently in development > (https://github.com/yuq/mesa-lima). > For that implementation, it seems that we need to have the minimum and > maximum index values from the index buffer available in order to set > up a proper command stream. > Mesa provides these values in pipe_draw_info.min_index and > pipe_draw_info.max_index, however in some cases we noticed that it > decides to not calculate those. This happens because of > st_context.draw_needs_minmax_index being false after evaluating the > vertex data. In those cases, min_index gets to be 0 and max_index gets > to be 0xffffffff. > According to the gallium documentation, this seems to be on purpose > and apparently drivers should be able to handle the 0 and 0xffffffff > case and be able to render anyway. However, we haven't figured out a > way to do the render anyway with 0 and 0xffffffff. > > For us it would be interesting to always have mesa calculate those > values for indexed drawing. We haven't been able to figure out a way > to do that without changing the mesa generic code. Is there some way > we could accomplish that in driver specific code? > Otherwise, can you provide some advice on how to best handle this? > > Using mesa 17.3 and kmscube with the following patch is one way to > reproduce st_context.draw_needs_minmax_index not being set. > https://gist.githubusercontent.com/enunes/366398fbee3d194deb > 3a46ef9c2ca78d/raw/82a2c8084236e35635b7a247609213d0068974e3/kmscube.patch > The only way that this works for us with the current implementation is > by hacking st_context.draw_needs_minmax_index to be always true in > some way. > > Thanks > > Erico > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev >
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