mesa: add EXT_texture_compression_latc

The encoding/decoding algorithms are shared with RGTC.
Thanks to some magic with the base format, the RGTC texstore functions work
for LATC too.

swrast passes the related piglit tests besides two things:
- The alpha channel is wrong (it's always 1), however the incorrect alpha
  channel makes some other tests fail too, so I guess it's unrelated to LATC.
- Signed LATC fetches aren't correct yet (signed values are clamped to [0,1]),
  however RGTC has the same problem.

Further testing (with other of my patches) shows that hardware drivers
and softpipe work.

BTW, ETQW uses this extension.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/mesa/main/image.c b/src/mesa/main/image.c
index 63936132f98..18abf2882af 100644
--- a/src/mesa/main/image.c
+++ b/src/mesa/main/image.c
@@ -743,6 +743,10 @@ _mesa_is_color_format(GLenum format)
       case GL_COMPRESSED_SIGNED_RED_RGTC1:
       case GL_COMPRESSED_RG_RGTC2:
       case GL_COMPRESSED_SIGNED_RG_RGTC2:
+      case GL_COMPRESSED_LUMINANCE_LATC1_EXT:
+      case GL_COMPRESSED_SIGNED_LUMINANCE_LATC1_EXT:
+      case GL_COMPRESSED_LUMINANCE_ALPHA_LATC2_EXT:
+      case GL_COMPRESSED_SIGNED_LUMINANCE_ALPHA_LATC2_EXT:
       /* signed, normalized texture formats */
       case GL_RGBA_SNORM:
       case GL_RGBA8_SNORM:
@@ -1025,6 +1029,11 @@ _mesa_is_compressed_format(struct gl_context *ctx, GLenum format)
    case GL_COMPRESSED_RG_RGTC2:
    case GL_COMPRESSED_SIGNED_RG_RGTC2:
       return ctx->Extensions.ARB_texture_compression_rgtc;
+   case GL_COMPRESSED_LUMINANCE_LATC1_EXT:
+   case GL_COMPRESSED_SIGNED_LUMINANCE_LATC1_EXT:
+   case GL_COMPRESSED_LUMINANCE_ALPHA_LATC2_EXT:
+   case GL_COMPRESSED_SIGNED_LUMINANCE_ALPHA_LATC2_EXT:
+      return ctx->Extensions.EXT_texture_compression_latc;
    default:
       return GL_FALSE;
    }