[Mesa-dev] [PATCH] gallivm: ignore rho approximation for cube maps

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

There's two reasons for this:
1) even when ignoring rho approximation for cube maps, the result is still
not correct, but it's better as the max error at edges is now sqrt(2) instead
of 2 (which was a full mip level), same as it is for ordinary 2d maps when
doing rho approximations (so the error actually goes from factor 2 at edges and
sqrt(2) completely inside a face to sqrt(2) at edges and 0 inside a face).
2) I want to repurpose rho_no_approx for cubemaps for fully correct cubemap
derivatives (so don't need yet another debug var).
---
 src/gallium/auxiliary/gallivm/lp_bld_sample.c |   34 +++++++++----------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample.c b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
index c775382..ea6bec7 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
@@ -269,10 +269,8 @@ lp_build_rho(struct lp_build_sample_context *bld,
       /* Could optimize this for single quad just skip the broadcast */
       cubesize = lp_build_extract_broadcast(gallivm, bld->float_size_in_type,
                                             rho_bld->type, float_size, index0);
-      if (no_rho_opt) {
-         /* skipping sqrt hence returning rho squared */
-         cubesize = lp_build_mul(rho_bld, cubesize, cubesize);
-      }
+      /* skipping sqrt hence returning rho squared */
+      cubesize = lp_build_mul(rho_bld, cubesize, cubesize);
       rho = lp_build_mul(rho_bld, cubesize, rho);
    }
    else if (derivs && !(bld->static_texture_state->target == PIPE_TEXTURE_CUBE)) {
@@ -757,8 +755,8 @@ lp_build_lod_selector(struct lp_build_sample_context *bld,
       }
       else {
          LLVMValueRef rho;
-         boolean rho_squared = (gallivm_debug & GALLIVM_DEBUG_NO_RHO_APPROX) &&
-                               (bld->dims > 1);
+         boolean rho_squared = ((gallivm_debug & GALLIVM_DEBUG_NO_RHO_APPROX) &&
+                                (bld->dims > 1)) || cube_rho;
 
          rho = lp_build_rho(bld, texture_unit, s, t, r, cube_rho, derivs);
 
@@ -1602,31 +1600,23 @@ lp_build_cube_lookup(struct lp_build_sample_context *bld,
           * know the texture is square which simplifies things (we can omit the
           * size mul which happens very early completely here and do it at the
           * very end).
+          * Also always do calculations according to GALLIVM_DEBUG_NO_RHO_APPROX
+          * since the error can get quite big otherwise at edges.
+          * (With no_rho_approx max error is sqrt(2) at edges, same as it is
+          * without no_rho_approx for 2d textures, otherwise it would be factor 2.)
           */
          ddx_ddy[0] = lp_build_packed_ddx_ddy_twocoord(coord_bld, s, t);
          ddx_ddy[1] = lp_build_packed_ddx_ddy_onecoord(coord_bld, r);
 
-         if (gallivm_debug & GALLIVM_DEBUG_NO_RHO_APPROX) {
-            ddx_ddy[0] = lp_build_mul(coord_bld, ddx_ddy[0], ddx_ddy[0]);
-            ddx_ddy[1] = lp_build_mul(coord_bld, ddx_ddy[1], ddx_ddy[1]);
-         }
-         else {
-            ddx_ddy[0] = lp_build_abs(coord_bld, ddx_ddy[0]);
-            ddx_ddy[1] = lp_build_abs(coord_bld, ddx_ddy[1]);
-         }
+         ddx_ddy[0] = lp_build_mul(coord_bld, ddx_ddy[0], ddx_ddy[0]);
+         ddx_ddy[1] = lp_build_mul(coord_bld, ddx_ddy[1], ddx_ddy[1]);
 
          tmp[0] = lp_build_swizzle_aos(coord_bld, ddx_ddy[0], swizzle01);
          tmp[1] = lp_build_swizzle_aos(coord_bld, ddx_ddy[0], swizzle23);
          tmp[2] = lp_build_swizzle_aos(coord_bld, ddx_ddy[1], swizzle02);
 
-         if (gallivm_debug & GALLIVM_DEBUG_NO_RHO_APPROX) {
-            rho_vec = lp_build_add(coord_bld, tmp[0], tmp[1]);
-            rho_vec = lp_build_add(coord_bld, rho_vec, tmp[2]);
-         }
-         else {
-            rho_vec = lp_build_max(coord_bld, tmp[0], tmp[1]);
-            rho_vec = lp_build_max(coord_bld, rho_vec, tmp[2]);
-         }
+         rho_vec = lp_build_add(coord_bld, tmp[0], tmp[1]);
+         rho_vec = lp_build_add(coord_bld, rho_vec, tmp[2]);
 
          tmp[0] = lp_build_swizzle_aos(coord_bld, rho_vec, swizzle0);
          tmp[1] = lp_build_swizzle_aos(coord_bld, rho_vec, swizzle1);
-- 
1.7.9.5