*/
+/**
+ * Do one perspective divide per quad.
+ *
+ * For perspective interpolation, the final attribute value is given
+ *
+ * a' = a/w = a * oow
+ *
+ * where
+ *
+ * a = a0 + dadx*x + dady*y
+ * w = w0 + dwdx*x + dwdy*y
+ * oow = 1/w = 1/(w0 + dwdx*x + dwdy*y)
+ *
+ * Instead of computing the division per pixel, with this macro we compute the
+ * division on the upper left pixel of each quad, and use a linear
+ * approximation in the remaining pixels, given by:
+ *
+ * da'dx = (dadx - dwdx*a)*oow
+ * da'dy = (dady - dwdy*a)*oow
+ *
+ * Ironically, this actually makes things slower -- probably because the
+ * divide hardware unit is rarely used, whereas the multiply unit is typically
+ * already saturated.
+ */
+#define PERSPECTIVE_DIVIDE_PER_QUAD 0
+
+
static const unsigned char quad_offset_x[4] = {0, 1, 0, 1};
static const unsigned char quad_offset_y[4] = {0, 0, 1, 1};
LLVMValueRef i1 = LLVMConstInt(LLVMInt32Type(), 1, 0);
LLVMValueRef i2 = LLVMConstInt(LLVMInt32Type(), 2, 0);
LLVMValueRef i3 = LLVMConstInt(LLVMInt32Type(), 3, 0);
- LLVMValueRef oow = NULL;
unsigned attrib;
unsigned chan;
a = LLVMBuildFAdd(builder, a, dadq2, "");
+#if PERSPECTIVE_DIVIDE_PER_QUAD
/*
- * a *= 1 / w
- * dadq *= 1 / w
+ * a *= 1 / w
*/
if (interp == LP_INTERP_PERSPECTIVE) {
LLVMValueRef w = bld->a[0][3];
assert(attrib != 0);
assert(bld->mask[0] & TGSI_WRITEMASK_W);
- if (!oow) {
- oow = lp_build_rcp(coeff_bld, w);
- lp_build_name(oow, "oow");
+ if (!bld->oow) {
+ bld->oow = lp_build_rcp(coeff_bld, w);
+ lp_build_name(bld->oow, "oow");
}
- a = lp_build_mul(coeff_bld, a, oow);
- dadq = lp_build_mul(coeff_bld, dadq, oow);
+ a = lp_build_mul(coeff_bld, a, bld->oow);
}
+#endif
attrib_name(a, attrib, chan, ".a");
attrib_name(dadq, attrib, chan, ".dadq");
{
struct lp_build_context *coeff_bld = &bld->coeff_bld;
LLVMValueRef shuffle = lp_build_const_int_vec(coeff_bld->type, quad_index);
+ LLVMValueRef oow = NULL;
unsigned attrib;
unsigned chan;
a = bld->attribs[0][chan];
}
else {
+ LLVMValueRef dadq;
+
a = bld->a[attrib][chan];
/*
a, coeff_bld->undef, shuffle, "");
/*
+ * Get the derivatives.
+ */
+
+ dadq = bld->dadq[attrib][chan];
+
+#if PERSPECTIVE_DIVIDE_PER_QUAD
+ if (interp == LP_INTERP_PERSPECTIVE) {
+ LLVMValueRef dwdq = bld->dadq[0][3];
+
+ if (oow == NULL) {
+ assert(bld->oow);
+ oow = LLVMBuildShuffleVector(coeff_bld->builder,
+ bld->oow, coeff_bld->undef,
+ shuffle, "");
+ }
+
+ dadq = lp_build_sub(coeff_bld,
+ dadq,
+ lp_build_mul(coeff_bld, a, dwdq));
+ dadq = lp_build_mul(coeff_bld, dadq, oow);
+ }
+#endif
+
+ /*
* Add the derivatives
*/
- a = lp_build_add(coeff_bld, a, bld->dadq[attrib][chan]);
+ a = lp_build_add(coeff_bld, a, dadq);
+
+#if !PERSPECTIVE_DIVIDE_PER_QUAD
+ if (interp == LP_INTERP_PERSPECTIVE) {
+ if (oow == NULL) {
+ LLVMValueRef w = bld->attribs[0][3];
+ assert(attrib != 0);
+ assert(bld->mask[0] & TGSI_WRITEMASK_W);
+ oow = lp_build_rcp(coeff_bld, w);
+ }
+ a = lp_build_mul(coeff_bld, a, oow);
+ }
+#endif
attrib_name(a, attrib, chan, "");
}