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llvmpipe: Prevent z > 1.0

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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.
This commit is contained in:
José Fonseca 2010-10-06 20:42:30 +01:00
parent 34c11c87e4
commit d0bfb3c514
1 changed files with 14 additions and 6 deletions
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20
src/gallium/drivers/llvmpipe/lp_bld_interp.c
View file

@ -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;