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 <[email protected]>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample.c b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
index d339abaea04..696855b1335 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;