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, 28 insertions, 0 deletions

diff --git a/src/mesa/main/texparam.c b/src/mesa/main/texparam.c
index e867dbf..bfb2e1b 100644
--- a/src/mesa/main/texparam.c
+++ b/src/mesa/main/texparam.c
@@ -451,6 +451,20 @@ set_tex_parameteri(struct gl_context *ctx,
       }
       goto invalid_pname;
 
+   case GL_DEPTH_STENCIL_TEXTURE_MODE:
+      if (_mesa_is_desktop_gl(ctx) && ctx->Extensions.ARB_stencil_texturing) {
+         bool stencil = params[0] == GL_STENCIL_INDEX;
+         if (!stencil && params[0] != GL_DEPTH_COMPONENT)
+            goto invalid_param;
+
+         if (texObj->StencilSampling == stencil)
+            return GL_FALSE;
+
+         texObj->StencilSampling = stencil;
+         return GL_TRUE;
+      }
+      goto invalid_pname;
+
    case GL_TEXTURE_CROP_RECT_OES:
       if (ctx->API != API_OPENGLES || !ctx->Extensions.OES_draw_texture)
          goto invalid_pname;
@@ -707,6 +721,7 @@ _mesa_TexParameterf(GLenum target, GLenum pname, GLfloat param)
    case GL_TEXTURE_COMPARE_MODE_ARB:
    case GL_TEXTURE_COMPARE_FUNC_ARB:
    case GL_DEPTH_TEXTURE_MODE_ARB:
+   case GL_DEPTH_STENCIL_TEXTURE_MODE:
    case GL_TEXTURE_SRGB_DECODE_EXT:
    case GL_TEXTURE_CUBE_MAP_SEAMLESS:
    case GL_TEXTURE_SWIZZLE_R_EXT:
@@ -762,6 +777,7 @@ _mesa_TexParameterfv(GLenum target, GLenum pname, const GLfloat *params)
    case GL_TEXTURE_COMPARE_MODE_ARB:
    case GL_TEXTURE_COMPARE_FUNC_ARB:
    case GL_DEPTH_TEXTURE_MODE_ARB:
+   case GL_DEPTH_STENCIL_TEXTURE_MODE:
    case GL_TEXTURE_SRGB_DECODE_EXT:
    case GL_TEXTURE_CUBE_MAP_SEAMLESS:
       {
@@ -1459,6 +1475,12 @@ _mesa_GetTexParameterfv( GLenum target, GLenum pname, GLfloat *params )
             goto invalid_pname;
          *params = (GLfloat) obj->DepthMode;
          break;
+      case GL_DEPTH_STENCIL_TEXTURE_MODE:
+         if (!_mesa_is_desktop_gl(ctx) || !ctx->Extensions.ARB_stencil_texturing)
+            goto invalid_pname;
+         *params = (GLfloat)
+            (obj->StencilSampling ? GL_STENCIL_INDEX : GL_DEPTH_COMPONENT);
+         break;
       case GL_TEXTURE_LOD_BIAS:
          if (_mesa_is_gles(ctx))
             goto invalid_pname;
@@ -1673,6 +1695,12 @@ _mesa_GetTexParameteriv( GLenum target, GLenum pname, GLint *params )
             goto invalid_pname;
          *params = (GLint) obj->DepthMode;
          break;
+      case GL_DEPTH_STENCIL_TEXTURE_MODE:
+         if (!_mesa_is_desktop_gl(ctx) || !ctx->Extensions.ARB_stencil_texturing)
+            goto invalid_pname;
+         *params = (GLint)
+            (obj->StencilSampling ? GL_STENCIL_INDEX : GL_DEPTH_COMPONENT);
+         break;
       case GL_TEXTURE_LOD_BIAS:
          if (_mesa_is_gles(ctx))
             goto invalid_pname;