Mesa (master): softpipe: fix Z interpolation invariance bug
Brian Paul
brianp at kemper.freedesktop.org
Tue Oct 4 21:06:49 UTC 2011
Module: Mesa
Branch: master
Commit: a5f2010735b6af469f57c6c254af9603bb9db18d
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=a5f2010735b6af469f57c6c254af9603bb9db18d
Author: Brian Paul <brianp at vmware.com>
Date: Tue Oct 4 15:01:05 2011 -0600
softpipe: fix Z interpolation invariance bug
We want quad/pixel Z values to be interpolated exactly the same for
multi-pass algorithms. Because of how the optimized Z-test code is
written, we can't cull the first quad in a run even if it's totally
killed. See the comment for more info.
NOTE: This is a candidate for the 7.11 branch.
---
src/gallium/drivers/softpipe/sp_quad_fs.c | 11 ++++++++++-
1 files changed, 10 insertions(+), 1 deletions(-)
diff --git a/src/gallium/drivers/softpipe/sp_quad_fs.c b/src/gallium/drivers/softpipe/sp_quad_fs.c
index d74d6d4..7b08cd0 100644
--- a/src/gallium/drivers/softpipe/sp_quad_fs.c
+++ b/src/gallium/drivers/softpipe/sp_quad_fs.c
@@ -118,7 +118,16 @@ shade_quads(struct quad_stage *qs,
machine->InterpCoefs = quads[0]->coef;
for (i = 0; i < nr; i++) {
- if (!shade_quad(qs, quads[i]))
+ /* Only omit this quad from the output list if all the fragments
+ * are killed _AND_ it's not the first quad in the list.
+ * The first quad is special in the (optimized) depth-testing code:
+ * the quads' Z coordinates are step-wise interpolated with respect
+ * to the first quad in the list.
+ * For multi-pass algorithms we need to produce exactly the same
+ * Z values in each pass. If interpolation starts with different quads
+ * we can get different Z values for the same (x,y).
+ */
+ if (!shade_quad(qs, quads[i]) && i > 0)
continue; /* quad totally culled/killed */
if (/*do_coverage*/ 0)
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