mesa: Add core API support for GL_ARB_stencil_texturing (from 4.3).

While the GL_ARB_stencil_texturing extension does not allow the creation
of stencil textures, it does allow shaders to sample stencil values
stored in packed depth/stencil textures.

Specifically, applications can call glTexParameter* with a pname of
GL_DEPTH_STENCIL_TEXTURE_MODE and value of either GL_DEPTH_COMPONENT or
GL_STENCIL_INDEX to select which component they wish to sample.  The
default value is GL_DEPTH_COMPONENT (for traditional depth sampling).

Shaders should use an unsigned integer sampler (presumably usampler2D)
to access stencil data.  Otherwise, results are undefined.  Using shadow
samplers with GL_STENCIL_INDEX selected also is undefined behavior.

This patch creates a new gl_texture_object field, StencilSampling, to
indicate that stencil should be sampled rather than depth.  (I chose to
use a boolean since I figured it would be more convenient for drivers.)
It also introduces the [Get]TexParameter code to get and set the value,
and of course the extension plumbing.

v2: Also consider textures incomplete when sampling stencil with
    non-NEAREST min/mag filters (caught by Eric Anholt).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/mesa/main/texobj.h b/src/mesa/main/texobj.h
index a4573b3..a9de73f 100644
--- a/src/mesa/main/texobj.h
+++ b/src/mesa/main/texobj.h
@@ -114,6 +114,20 @@ _mesa_is_texture_complete(const struct gl_texture_object *texObj,
       return GL_FALSE;
    }
 
+   /* From the ARB_stencil_texturing specification:
+    * "Add a new bullet point for the conditions that cause the texture
+    *  to not be complete:
+    *
+    *  * The internal format of the texture is DEPTH_STENCIL, the
+    *    DEPTH_STENCIL_TEXTURE_MODE for the texture is STENCIL_INDEX and either
+    *    the magnification filter or the minification filter is not NEAREST."
+    */
+   if (texObj->StencilSampling &&
+       texObj->Image[0][texObj->BaseLevel]->_BaseFormat == GL_DEPTH_STENCIL &&
+       (sampler->MagFilter != GL_NEAREST || sampler->MinFilter != GL_NEAREST)) {
+      return GL_FALSE;
+   }
+
    if (_mesa_is_mipmap_filter(sampler))
       return texObj->_MipmapComplete;
    else