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 <[email protected]>
Reviewed-by: Matt Turner <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mesa/main/texobj.c b/src/mesa/main/texobj.c
index 3375fe36bc5..8bdbb08c8ea 100644
--- a/src/mesa/main/texobj.c
+++ b/src/mesa/main/texobj.c
@@ -148,6 +148,7 @@ _mesa_initialize_texture_object( struct gl_context *ctx,
    obj->Sampler.CompareMode = GL_NONE;         /* ARB_shadow */
    obj->Sampler.CompareFunc = GL_LEQUAL;       /* ARB_shadow */
    obj->DepthMode = ctx->API == API_OPENGL_CORE ? GL_RED : GL_LUMINANCE;
+   obj->StencilSampling = false;
    obj->Sampler.CubeMapSeamless = GL_FALSE;
    obj->Swizzle[0] = GL_RED;
    obj->Swizzle[1] = GL_GREEN;
@@ -280,6 +281,7 @@ _mesa_copy_texture_object( struct gl_texture_object *dest,
    dest->Sampler.CompareFunc = src->Sampler.CompareFunc;
    dest->Sampler.CubeMapSeamless = src->Sampler.CubeMapSeamless;
    dest->DepthMode = src->DepthMode;
+   dest->StencilSampling = src->StencilSampling;
    dest->Sampler.sRGBDecode = src->Sampler.sRGBDecode;
    dest->_MaxLevel = src->_MaxLevel;
    dest->_MaxLambda = src->_MaxLambda;