Mesa (master): gallivm: add comment for bogus min/ mag filter selection with nearest mip filter

[Roland Scheidegger]

Module: Mesa
Branch: master
Commit: 275d2efeed79f135bbcc512bcf2c0607f2f25cd1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=275d2efeed79f135bbcc512bcf2c0607f2f25cd1

Author: Roland Scheidegger <sroland at vmware.com>
Date:   Wed Aug 21 20:35:51 2013 +0200

gallivm: add comment for bogus min/mag filter selection with nearest mip filter

Detected this hunting some other bug, not sure if it really needs fixing but
it is definitely wrong.

Reviewed-by: Jose Fonseca <jfonseca at vmware.com>

---

 src/gallium/auxiliary/gallivm/lp_bld_sample.c     |    8 ++++++++
 src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c |    2 +-
 src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c |    2 +-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample.c b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
index d339aba..696855b 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
@@ -700,6 +700,14 @@ lp_build_lod_selector(struct lp_build_sample_context *bld,
 
             if (mip_filter == PIPE_TEX_MIPFILTER_NONE ||
                 mip_filter == PIPE_TEX_MIPFILTER_NEAREST) {
+               /*
+                * XXX: this is not entirely correct, as out_lod_ipart is used
+                * both for mip level determination as well as mag/min switchover
+                * point (if different min/mag filters are used). In particular,
+                * lod values between [-0.5,0] (rho between [sqrt(2), 1.0]) will
+                * incorrectly use min filter instead of mag (the non-optimized
+                * calculation further down has exactly the same problem).
+                */
                *out_lod_ipart = lp_build_ilog2(levelf_bld, rho);
                *out_lod_fpart = levelf_bld->zero;
                return;
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c b/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c
index da416aa..2573cec 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c
@@ -1611,7 +1611,7 @@ lp_build_sample_aos(struct lp_build_sample_context *bld,
       LLVMValueRef minify;
 
       /*
-       * XXX this should to all lods into account, if some are min
+       * XXX this should take all lods into account, if some are min
        * some max probably could hack up the coords/weights in the linear
        * path with selects to work for nearest.
        * If that's just two quads sitting next to each other it seems
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
index 6d12587..34ab414 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
@@ -1636,7 +1636,7 @@ lp_build_sample_general(struct lp_build_sample_context *bld,
       LLVMValueRef minify;
 
       /*
-       * XXX this should to all lods into account, if some are min
+       * XXX this should take all lods into account, if some are min
        * some max probably could hack up the coords/weights in the linear
        * path with selects to work for nearest.
        * If that's just two quads sitting next to each other it seems