st/mesa: add fallback pipe formats for (compressed) R, RG formats

If we don't find an exact PIPE_FORMAT_x for a GL_(COMPRESSED)_RED/RG format,
try uncompressed formats.  We were already doing this for the RGB(A) formats.

Fixes piglit arb_texture_compression-internal-format-query test.

NOTE: This is a candidate for the stable branches.

Reviewed-by: José Fonseca <jfonseca@vmware.com>

src/mesa/state_tracker/st_format.c

@@ -839,6 +839,15 @@ struct format_mapping
       PIPE_FORMAT_S8_UINT_Z24_UNORM, \
       0
 
+#define DEFAULT_SNORM8_RGBA_FORMATS \
+      PIPE_FORMAT_R8G8B8A8_SNORM, \
+      0
+
+#define DEFAULT_UNORM16_RGBA_FORMATS \
+      PIPE_FORMAT_R16G16B16A16_UNORM, \
+      DEFAULT_RGBA_FORMATS
+
+
 /**
  * This table maps OpenGL texture format enums to Gallium pipe_format enums.
  * Multiple GL enums might map to multiple pipe_formats.
@@ -1145,54 +1154,55 @@ static const struct format_mapping format_map[] = {
    /* R, RG formats */
    {
       { GL_RED, GL_R8, 0 },
-      { PIPE_FORMAT_R8_UNORM, 0 }
+      { PIPE_FORMAT_R8_UNORM, PIPE_FORMAT_R8G8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_RG, GL_RG8, 0 },
-      { PIPE_FORMAT_R8G8_UNORM, 0 }
+      { PIPE_FORMAT_R8G8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_R16, 0 },
-      { PIPE_FORMAT_R16_UNORM, 0 }
+      { PIPE_FORMAT_R16_UNORM, PIPE_FORMAT_R16G16_UNORM,
+        DEFAULT_UNORM16_RGBA_FORMATS }
    },
    {
       { GL_RG16, 0 },
-      { PIPE_FORMAT_R16G16_UNORM, 0 }
+      { PIPE_FORMAT_R16G16_UNORM, DEFAULT_UNORM16_RGBA_FORMATS }
    },
 
    /* compressed R, RG formats */
    {
       { GL_COMPRESSED_RED, GL_COMPRESSED_RED_RGTC1, 0 },
-      { PIPE_FORMAT_RGTC1_UNORM, PIPE_FORMAT_R8_UNORM, 0 }
+      { PIPE_FORMAT_RGTC1_UNORM, PIPE_FORMAT_R8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_SIGNED_RED_RGTC1, 0 },
-      { PIPE_FORMAT_RGTC1_SNORM, 0 }
+      { PIPE_FORMAT_RGTC1_SNORM, DEFAULT_SNORM8_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_RG, GL_COMPRESSED_RG_RGTC2, 0 },
-      { PIPE_FORMAT_RGTC2_UNORM, PIPE_FORMAT_R8G8_UNORM, 0 }
+      { PIPE_FORMAT_RGTC2_UNORM, PIPE_FORMAT_R8G8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_SIGNED_RG_RGTC2, 0 },
-      { PIPE_FORMAT_RGTC2_SNORM, 0 }
+      { PIPE_FORMAT_RGTC2_SNORM, DEFAULT_SNORM8_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_LUMINANCE, GL_COMPRESSED_LUMINANCE_LATC1_EXT, 0 },
-      { PIPE_FORMAT_LATC1_UNORM, PIPE_FORMAT_L8_UNORM, 0 }
+      { PIPE_FORMAT_LATC1_UNORM, PIPE_FORMAT_L8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_SIGNED_LUMINANCE_LATC1_EXT, 0 },
-      { PIPE_FORMAT_LATC1_SNORM, 0 }
+      { PIPE_FORMAT_LATC1_SNORM, DEFAULT_SNORM8_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_LUMINANCE_ALPHA, GL_COMPRESSED_LUMINANCE_ALPHA_LATC2_EXT,
         GL_COMPRESSED_LUMINANCE_ALPHA_3DC_ATI, 0 },
-      { PIPE_FORMAT_LATC2_UNORM, PIPE_FORMAT_L8A8_UNORM, 0 }
+      { PIPE_FORMAT_LATC2_UNORM, PIPE_FORMAT_L8A8_UNORM, DEFAULT_RGBA_FORMATS }
    },
    {
       { GL_COMPRESSED_SIGNED_LUMINANCE_ALPHA_LATC2_EXT, 0 },
-      { PIPE_FORMAT_LATC2_SNORM, 0 }
+      { PIPE_FORMAT_LATC2_SNORM, DEFAULT_SNORM8_RGBA_FORMATS }
    },
 
    /* ETC1 */