mesa: Add support for querying GL_FRAGMENT_SHADER_DISCARDS_SAMPLES_EXT.

This can currently only give true as result since the only way you can
expose EXT_shader_framebuffer_fetch right now is by flipping the
MESA_shader_framebuffer_fetch bit, but that could potentially change
in the future, see [1] for an explanation.

[1] https://lists.freedesktop.org/archives/mesa-dev/2016-July/124028.html

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/main/get.c

@@ -530,6 +530,13 @@ static const int extra_core_ARB_color_buffer_float_and_new_buffers[] = {
    EXTRA_END
 };
 
+static const int extra_EXT_shader_framebuffer_fetch[] = {
+   EXTRA_API_ES2,
+   EXTRA_API_ES3,
+   EXT(MESA_shader_framebuffer_fetch),
+   EXTRA_END
+};
+
 /* This is the big table describing all the enums we accept in
  * glGet*v().  The table is partitioned into six parts: enums
  * understood by all GL APIs (OpenGL, GLES and GLES2), enums shared

src/mesa/main/get_hash_params.py

@@ -424,6 +424,10 @@ descriptor=[
 ]},
 
 { "apis": ["GLES", "GLES2"], "params": [
+# GL_EXT_shader_framebuffer_fetch.  Should be true if the MESA framebuffer
+# fetch extension is supported since the latter imposes no restrictions on
+# non-uniform per-sample discard.
+  [ "FRAGMENT_SHADER_DISCARDS_SAMPLES_EXT", "CONTEXT_BOOL(Extensions.MESA_shader_framebuffer_fetch), extra_EXT_shader_framebuffer_fetch" ],
 # GL_OES_EGL_image_external
   [ "TEXTURE_BINDING_EXTERNAL_OES", "LOC_CUSTOM, TYPE_INT, TEXTURE_EXTERNAL_INDEX, extra_OES_EGL_image_external" ],
   [ "TEXTURE_EXTERNAL_OES", "LOC_CUSTOM, TYPE_BOOLEAN, 0, extra_OES_EGL_image_external" ],

src/mesa/main/glheader.h

@@ -140,6 +140,9 @@ typedef void *GLeglImageOES;
 #define GL_ETC1_RGB8_OES                                        0x8D64
 #endif
 
+#ifndef GL_EXT_shader_framebuffer_fetch
+#define GL_FRAGMENT_SHADER_DISCARDS_SAMPLES_EXT                 0x8A52
+#endif
 
 /* Inexplicably, GL_HALF_FLOAT_OES has a different value than GL_HALF_FLOAT.
  */