glsl: Add new builtins required by GL_ARB_sample_shading

New builtins added by GL_ARB_sample_shading:
in vec2 gl_SamplePosition
in int gl_SampleID
in int gl_NumSamples
out int gl_SampleMask[]

V2: - Use SWIZZLE_XXXX for STATE_NUM_SAMPLES.
    - Use "result.samplemask" in arb_output_attrib_string.
    - Add comment to explain the size of gl_SampleMask[] array.
    - Make gl_SampleID and gl_SamplePosition system values.
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/src/glsl/builtin_variables.cpp b/src/glsl/builtin_variables.cpp
index 7a3505ace12..4d441045a83 100644
--- a/src/glsl/builtin_variables.cpp
+++ b/src/glsl/builtin_variables.cpp
@@ -30,6 +30,9 @@
 #include "program/prog_statevars.h"
 #include "program/prog_instruction.h"
 
+static struct gl_builtin_uniform_element gl_NumSamples_elements[] = {
+   {NULL, {STATE_NUM_SAMPLES, 0, 0}, SWIZZLE_XXXX}
+};
 
 static struct gl_builtin_uniform_element gl_DepthRange_elements[] = {
    {"near", {STATE_DEPTH_RANGE, 0, 0}, SWIZZLE_XXXX},
@@ -236,6 +239,7 @@ static struct gl_builtin_uniform_element gl_NormalMatrix_elements[] = {
 #define STATEVAR(name) {#name, name ## _elements, Elements(name ## _elements)}
 
 static const struct gl_builtin_uniform_desc _mesa_builtin_uniform_desc[] = {
+   STATEVAR(gl_NumSamples),
    STATEVAR(gl_DepthRange),
    STATEVAR(gl_ClipPlane),
    STATEVAR(gl_Point),
@@ -662,6 +666,7 @@ builtin_variable_generator::generate_constants()
 void
 builtin_variable_generator::generate_uniforms()
 {
+   add_uniform(int_t, "gl_NumSamples");
    add_uniform(type("gl_DepthRangeParameters"), "gl_DepthRange");
    add_uniform(array(vec4_t, VERT_ATTRIB_MAX), "gl_CurrentAttribVertMESA");
    add_uniform(array(vec4_t, VARYING_SLOT_MAX), "gl_CurrentAttribFragMESA");
@@ -838,6 +843,19 @@ builtin_variable_generator::generate_fs_special_vars()
       if (state->AMD_shader_stencil_export_warn)
          var->warn_extension = "GL_AMD_shader_stencil_export";
    }
+
+   if (state->ARB_sample_shading_enable) {
+      add_system_value(SYSTEM_VALUE_SAMPLE_ID, int_t, "gl_SampleID");
+      add_system_value(SYSTEM_VALUE_SAMPLE_POS, vec2_t, "gl_SamplePosition");
+      /* From the ARB_sample_shading specification:
+       *    "The number of elements in the array is ceil(<s>/32), where
+       *    <s> is the maximum number of color samples supported by the
+       *    implementation."
+       * Since no drivers expose more than 32x MSAA, we can simply set
+       * the array size to 1 rather than computing it.
+       */
+      add_output(FRAG_RESULT_SAMPLE_MASK, array(int_t, 1), "gl_SampleMask");
+   }
 }