Cleanup some shader #defines

- create a new FILAMENT_HAS_FEATURE_TEXTURE_GATHER, which can be used
  in the shaders to use textureGather.

- A new TARGET_GLES_ENVIRONMENT and TARGET_GL_ENVIRONMENT in addition
  to TARGET_METAL_ and TARGET_VULKAN_, for completeness.

- Rename TARGET_LANGUAGE_SPIRV to FILAMENT_VULKAN_SEMANTICS and add
  FILAMENT_OPENGL_SEMANTICS for completeness.

- expose the shader model to shaders as: FILAMENT_SHADER_MODEL_ES30 and
  FILAMENT_SHADER_MODEL_GL41

Use these new #define where appropriate.

The main change here is that TARGET_MOBILE is now only used for dealing
with the `mediump` default on mobile.

This change also enables textureGather on Metal.

filament/src/materials/antiAliasing/fxaa.fs

@@ -2,7 +2,7 @@
 #define gpu_shader5        1
 
 // ES 3.0 does not have gather though
-#if defined(TARGET_VULKAN_ENVIRONMENT) || !defined(TARGET_MOBILE)
+#if defined(FILAMENT_HAS_FEATURE_TEXTURE_GATHER)
 #define FXAA_GATHER4_ALPHA 1
 #else
 #define FXAA_GATHER4_ALPHA 0

filament/src/materials/dof/dofDownsample.mat

@@ -78,7 +78,7 @@ void postProcess(inout PostProcessInputs postProcess) {
     hdr[3] = 1.0 / (1.0 + max3(s00.rgb));
 
     vec4 d;
-#if defined(TARGET_VULKAN_ENVIRONMENT) || !defined(TARGET_MOBILE)
+#if defined(FILAMENT_HAS_FEATURE_TEXTURE_GATHER)
     d = textureGather(materialParams_depth, uv, 0); // 01, 11, 10, 00
 #else
     d[0] = textureLodOffset(materialParams_depth, uv, 0.0, ivec2(0, 1)).r;

filament/src/materials/dof/dofTiles.mat

@@ -48,7 +48,7 @@ void postProcess(inout PostProcessInputs postProcess) {
 
     // note: the first time, the source texture is swizzled -- so .r and .g are the same channel
     // if swizzling is not supported, we use dofTilesSwizzle instead.
-#if defined(TARGET_VULKAN_ENVIRONMENT) || !defined(TARGET_MOBILE)
+#if defined(FILAMENT_HAS_FEATURE_TEXTURE_GATHER)
     vec4 mi = textureGather(materialParams_cocMinMax, uv, 0); // 01, 11, 10, 00
     vec4 ma = textureGather(materialParams_cocMinMax, uv, 1); // 01, 11, 10, 00
 #else

filament/src/materials/dof/dofTilesSwizzle.mat

@@ -46,7 +46,7 @@ void postProcess(inout PostProcessInputs postProcess) {
 
     ivec2 i = ivec2(uv * size - 0.5);
 
-#if defined(TARGET_VULKAN_ENVIRONMENT) || !defined(TARGET_MOBILE)
+#if defined(FILAMENT_HAS_FEATURE_TEXTURE_GATHER)
     vec4 mi = textureGather(materialParams_cocMinMax, uv, 0); // 01, 11, 10, 00
 #else
     vec4 mi;

libs/filamat/include/filamat/MaterialBuilder.h

@@ -68,8 +68,8 @@ public:
     };
 
     enum class TargetLanguage {
-        GLSL,
-        SPIRV
+        GLSL,           // GLSL with OpenGL semantics
+        SPIRV           // GLSL with Vulkan semantics
     };
 
     enum class Optimization {

libs/filamat/src/shaders/CodeGenerator.cpp

@@ -18,9 +18,13 @@
 
 #include "generated/shaders.h"
 
+#include <utils/sstream.h>
+
 #include <cctype>
 #include <iomanip>
 
+#include <assert.h>
+
 namespace filamat {
 
 // From driverEnum namespace
@@ -74,8 +78,26 @@ io::sstream& CodeGenerator::generateProlog(io::sstream& out, ShaderType type,
     if (mTargetApi == TargetApi::METAL) {
         out << "#define TARGET_METAL_ENVIRONMENT\n";
     }
+    if (mTargetApi == TargetApi::OPENGL && mShaderModel == ShaderModel::GL_ES_30) {
+        out << "#define TARGET_GLES_ENVIRONMENT\n";
+    }
+    if (mTargetApi == TargetApi::OPENGL && mShaderModel == ShaderModel::GL_CORE_41) {
+        out << "#define TARGET_GL_ENVIRONMENT\n";
+    }
+
+    out << '\n';
     if (mTargetLanguage == TargetLanguage::SPIRV) {
-        out << "#define TARGET_LANGUAGE_SPIRV\n";
+        out << "#define FILAMENT_VULKAN_SEMANTICS\n";
+    }
+    if (mTargetLanguage == TargetLanguage::GLSL) {
+        out << "#define FILAMENT_OPENGL_SEMANTICS\n";
+    }
+
+    out << '\n';
+    if (mTargetApi == TargetApi::VULKAN ||
+        mTargetApi == TargetApi::METAL ||
+        mTargetApi == TargetApi::OPENGL && mShaderModel == ShaderModel::GL_CORE_41) {
+        out << "#define FILAMENT_HAS_FEATURE_TEXTURE_GATHER\n";
     }
 
     out << '\n';

shaders/src/ambient_occlusion.fs

@@ -27,7 +27,11 @@ float evaluateSSAO() {
         highp vec2 size = vec2(textureSize(light_ssao, 0));
 
         // Read four AO samples and their depths values
-#if defined(TARGET_MOBILE)
+#if defined(FILAMENT_HAS_FEATURE_TEXTURE_GATHER)
+        vec4 ao = textureGather(light_ssao, uv, 0); // 01, 11, 10, 00
+        vec4 dg = textureGather(light_ssao, uv, 1); // 01, 11, 10, 00
+        vec4 db = textureGather(light_ssao, uv, 2); // 01, 11, 10, 00
+#else
         // on mobile we can't use textureGather() because we're limited to ES3.0,
         // so we emulate it with  texelFetch(), on Pixel 4 this doesn't seem to have any
         // significant impact on performance.
@@ -38,10 +42,6 @@ float evaluateSSAO() {
         vec4 ao = vec4(s01.r, s11.r, s10.r, s00.r);
         vec4 dg = vec4(s01.g, s11.g, s10.g, s00.g);
         vec4 db = vec4(s01.b, s11.b, s10.b, s00.b);
-#else
-        vec4 ao = textureGather(light_ssao, uv, 0); // 01, 11, 10, 00
-        vec4 dg = textureGather(light_ssao, uv, 1); // 01, 11, 10, 00
-        vec4 db = textureGather(light_ssao, uv, 2); // 01, 11, 10, 00
 #endif
         // bilinear weights
         vec2 f = fract(uv * size - 0.5);

shaders/src/common_types.fs

@@ -1,4 +1,4 @@
-#if !defined(TARGET_MOBILE) || defined(TARGET_LANGUAGE_SPIRV)
+#if defined(FILAMENT_VULKAN_SEMANTICS)
 #define LAYOUT_LOCATION(x) layout(location = x)
 #else
 #define LAYOUT_LOCATION(x)