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authorPaul Berry <[email protected]>2012-12-15 13:06:10 -0800
committerPaul Berry <[email protected]>2012-12-18 09:02:49 -0800
commit1ad516207d2297b14fe26627e5bb599a9f704ac5 (patch)
tree66940b4f0d1dd752edf901c2755dd0a20addfe9c /src/mesa/swrast_setup/NOTES
parentb87e65c3b61caeaa4f97a34d62e148e59a0dd5b8 (diff)
mesa: Fix corner cases of BindBufferBase with transform feedback.
This patch implements the following behaviours, which are mandated by the GL 4.3 and GLES3 specs. 1. Regarding the GL_TRANSFORM_FEEDBACK_BUFFER_SIZE query: "If the ... size was not specified when the buffer object was bound (e.g. if it was bound with BindBufferBase), ... zero is returned." (GL 4.3 section 6.7.1 "Indexed Buffer Object Limits and Binding Queries"). 2. "BindBufferBase binds the entire buffer, even when the size of the buffer is changed after the binding is established. It is equivalent to calling BindBufferRange with offset zero, while size is determined by the size of the bound buffer at the time the binding is used." (GL 4.3 section 6.1.1 "Binding Buffer Objects to Indexed Targets"). I interpret "at the time the binding is used" to mean "at the time of the call to glBeginTransformFeedback". 3. "Regardless of the size specified with BindBufferRange, or indirectly with BindBufferBase, the GL will never read or write beyond the end of a bound buffer. In some cases this constraint may result in visibly different behavior when a buffer overflow would otherwise result, such as described for transform feedback operations in section 13.2.2." (GL 4.3 section 6.1.1 "Binding Buffer Objects to Indexed Targets"). Item 1 has been part of the spec all the way back to the inception of the EXT_transform_feedback extension. Items 2 and 3 were added in GL 4.2 and GLES 3. Prior to GL 4.2, in place of items 2 and 3, the spec simply said "BindBufferBase is equivalent to calling BindBufferRange with offset zero and size equal to the size of buffer." For transform feedback, Mesa behaved as though this meant "...equal to the size of buffer at the time of the call to BindBufferBase". However, this was problematic because it left it ambiguous what to do if the buffer is shrunk between the call to BindBuffer{Base,Range} and the call to BeginTransformFeedback. Prior to this patch, Mesa's behaviour was to try to write beyond the end of the buffer, likely resulting in memory corruption. In light of this, I'm interpreting the spec change as a clarification, not an intended behavioural change, so I'm making the change apply regardless of API version. Fixes GLES3 conformance test transform_feedback2_pause_resume.test. Reviewed-by: Jordan Justen <[email protected]>
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