Mesa (master): llvmpipe: Prevent z > 1.0
Jose Fonseca
jrfonseca at kemper.freedesktop.org
Sat Oct 9 08:40:40 UTC 2010
Module: Mesa
Branch: master
Commit: d0bfb3c5144a9434efd4d53ced149d42016b5bdc
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=d0bfb3c5144a9434efd4d53ced149d42016b5bdc
Author: José Fonseca <jfonseca at vmware.com>
Date: Wed Oct 6 20:42:30 2010 +0100
llvmpipe: Prevent z > 1.0
The current interpolation schemes causes precision loss.
Changing the operation order helps, but does not completely avoid the
problem.
The only short term solution is to clamp z to 1.0.
This is unfortunate, but probably unavoidable until interpolation is
improved.
---
src/gallium/drivers/llvmpipe/lp_bld_interp.c | 20 ++++++++++++++------
1 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/src/gallium/drivers/llvmpipe/lp_bld_interp.c b/src/gallium/drivers/llvmpipe/lp_bld_interp.c
index 2a374f8..ee92ce3 100644
--- a/src/gallium/drivers/llvmpipe/lp_bld_interp.c
+++ b/src/gallium/drivers/llvmpipe/lp_bld_interp.c
@@ -206,7 +206,7 @@ coeffs_init(struct lp_build_interp_soa_context *bld,
dadq2 = LLVMBuildFAdd(builder, dadq, dadq, "");
/*
- * a = a0 + x * dadx + y * dady
+ * a = a0 + (x * dadx + y * dady)
*/
if (attrib == 0 && chan == 0) {
@@ -219,11 +219,11 @@ coeffs_init(struct lp_build_interp_soa_context *bld,
a = a0;
if (interp != LP_INTERP_CONSTANT &&
interp != LP_INTERP_FACING) {
- LLVMValueRef tmp;
- tmp = LLVMBuildFMul(builder, bld->x, dadx, "");
- a = LLVMBuildFAdd(builder, a, tmp, "");
- tmp = LLVMBuildFMul(builder, bld->y, dady, "");
- a = LLVMBuildFAdd(builder, a, tmp, "");
+ LLVMValueRef ax, ay, axy;
+ ax = LLVMBuildFMul(builder, bld->x, dadx, "");
+ ay = LLVMBuildFMul(builder, bld->y, dady, "");
+ axy = LLVMBuildFAdd(builder, ax, ay, "");
+ a = LLVMBuildFAdd(builder, a, axy, "");
}
}
@@ -350,6 +350,14 @@ attribs_update(struct lp_build_interp_soa_context *bld, int quad_index)
}
#endif
+ if (attrib == 0 && chan == 2) {
+ /* FIXME: Depth values can exceed 1.0, due to the fact that
+ * setup interpolation coefficients refer to (0,0) which causes
+ * precision loss. So we must clamp to 1.0 here to avoid artifacts
+ */
+ a = lp_build_min(coeff_bld, a, coeff_bld->one);
+ }
+
attrib_name(a, attrib, chan, "");
}
bld->attribs[attrib][chan] = a;
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