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 <[email protected]>
Reviewed-by: Paul Berry <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>

3 files changed, 28 insertions, 1 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");
+   }
 }
 
 
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 4774c8eb04c..b5c5583d6d3 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -274,6 +274,11 @@ typedef enum
 #define VARYING_BIT_VAR(V) BITFIELD64_BIT(VARYING_SLOT_VAR0 + (V))
 /*@}*/
 
+/**
+ * Bitflags for system values.
+ */
+#define SYSTEM_BIT_SAMPLE_ID BITFIELD64_BIT(SYSTEM_VALUE_SAMPLE_ID)
+#define SYSTEM_BIT_SAMPLE_POS BITFIELD64_BIT(SYSTEM_VALUE_SAMPLE_POS)
 
 /**
  * Determine if the given gl_varying_slot appears in the fragment shader.
@@ -306,12 +311,13 @@ typedef enum
     * register is written.  No FRAG_RESULT_DATAn will be written.
     */
    FRAG_RESULT_COLOR = 2,
+   FRAG_RESULT_SAMPLE_MASK = 3,
 
    /* FRAG_RESULT_DATAn are the per-render-target (GLSL gl_FragData[n]
     * or ARB_fragment_program fragment.color[n]) color results.  If
     * any are written, FRAG_RESULT_COLOR will not be written.
     */
-   FRAG_RESULT_DATA0 = 3,
+   FRAG_RESULT_DATA0 = 4,
    FRAG_RESULT_MAX = (FRAG_RESULT_DATA0 + MAX_DRAW_BUFFERS)
 } gl_frag_result;
 
@@ -1904,6 +1910,8 @@ typedef enum
    SYSTEM_VALUE_FRONT_FACE,  /**< Fragment shader only (not done yet) */
    SYSTEM_VALUE_VERTEX_ID,   /**< Vertex shader only */
    SYSTEM_VALUE_INSTANCE_ID, /**< Vertex shader only */
+   SYSTEM_VALUE_SAMPLE_ID,   /**< Fragment shader only */
+   SYSTEM_VALUE_SAMPLE_POS,  /**< Fragment shader only */
    SYSTEM_VALUE_MAX          /**< Number of values */
 } gl_system_value;
 
diff --git a/src/mesa/program/prog_print.c b/src/mesa/program/prog_print.c
index cf852132d04..fa9063f5b9d 100644
--- a/src/mesa/program/prog_print.c
+++ b/src/mesa/program/prog_print.c
@@ -311,6 +311,7 @@ arb_output_attrib_string(GLint index, GLenum progType)
       "result.depth", /* FRAG_RESULT_DEPTH */
       "result.(one)", /* FRAG_RESULT_STENCIL */
       "result.color", /* FRAG_RESULT_COLOR */
+      "result.samplemask", /* FRAG_RESULT_SAMPLE_MASK */
       "result.color[0]", /* FRAG_RESULT_DATA0 (named for GLSL's gl_FragData) */
       "result.color[1]",
       "result.color[2]",