[Mesa-dev] Review request: [PATCH] Fix grabbing the wrong variant if glDrawPixels is called

[Matias N. Goldberg]

Hi!I just subscribed to this dev list.
I wrote this patch (copy at the end of this email)https://bugs.freedesktop.org/attachment.cgi?id=132462&action=edit
in order to fix bug Bug 101596 - Blender renders black UI elements (https://bugs.freedesktop.org/show_bug.cgi?id=101596)Note that this bug may not only affect Mesa.
I am asking for this patch to be reviewed for inclusion in Mesa.

Thanks
Matias

>From 3db888f8645acd5d41b689ee6522d465bcf71044 Mon Sep 17 00:00:00 2001
Message-Id: <3db888f8645acd5d41b689ee6522d465bcf71044.1499274200.git.dark_sylinc at yahoo.com.ar>
From: "Matias N. Goldberg" <dark_sylinc at yahoo.com.ar>
Date: Wed, 5 Jul 2017 14:02:50 -0300
Subject: [PATCH] Fix grabbing the wrong variant if glDrawPixels is called

By design pixel shaders can have up to 3 variants:
* The standard one.
* glDrawPixels variant.
* glBitmap variant.
However "shader_has_one_variant" ignores this fact, and therefore
st_update_fp would select the wrong variant if glDrawPixels or glBitmap
was ever called.

This patch fixes the problem. If the standard variant has been created,
calling glDrawPixels or glBitmap will append the variant to the second
entry of the linked list, so that st_update_fp still selects the right
one if shader_has_one_variant is set.

If the standard variant hasn't been created yet and glDrawPixel/Bitmap
has been called, st_update_fp will will see this and take the slow path
instead. The standard variant will then be added at the front of the
linked list, so that the next time the fast path is taken.

Blender in particular is hit by this bug.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=101596
---
 src/mesa/state_tracker/st_atom_shader.c |  4 +++-
 src/mesa/state_tracker/st_program.c     | 23 ++++++++++++++++++++---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/mesa/state_tracker/st_atom_shader.c b/src/mesa/state_tracker/st_atom_shader.c
index c1869d323b..07cf54f555 100644
--- a/src/mesa/state_tracker/st_atom_shader.c
+++ b/src/mesa/state_tracker/st_atom_shader.c
@@ -108,7 +108,9 @@ st_update_fp( struct st_context *st )
    if (st->shader_has_one_variant[MESA_SHADER_FRAGMENT] &&
        !stfp->ati_fs && /* ATI_fragment_shader always has multiple variants */
        !stfp->Base.ExternalSamplersUsed && /* external samplers need variants */
-       stfp->variants) {
+       stfp->variants &&
+       !stfp->variants->key.drawpixels &&
+       !stfp->variants->key.bitmap ) {
       shader = stfp->variants->driver_shader;
    } else {
       memset(&key, 0, sizeof(key));
diff --git a/src/mesa/state_tracker/st_program.c b/src/mesa/state_tracker/st_program.c
index 6de61741dc..86faf5982d 100644
--- a/src/mesa/state_tracker/st_program.c
+++ b/src/mesa/state_tracker/st_program.c
@@ -1322,9 +1322,26 @@ st_get_fp_variant(struct st_context *st,
       /* create new */
       fpv = st_create_fp_variant(st, stfp, key);
       if (fpv) {
-         /* insert into list */
-         fpv->next = stfp->variants;
-         stfp->variants = fpv;
+         if( key->bitmap || key->drawpixels ) {
+            /* Regular variants should always come before the
+               bitmap & drawpixels variants, (unless there
+               are no regular variants) so that
+               st_update_fp can take a fast path when
+               shader_has_one_variant is set.
+            */
+            /* insert into list */
+            if( !stfp->variants ) {
+               fpv->next = stfp->variants;
+               stfp->variants = fpv;
+            } else {
+               fpv->next = stfp->variants->next;
+               stfp->variants->next = fpv;
+            }
+         } else {
+            /* insert into list */
+            fpv->next = stfp->variants;
+            stfp->variants = fpv;
+         }
       }
    }
 
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