On Desktop GL, require index-constant sampler array indexing

src/compiler/translator/TranslatorGLSL.cpp

@@ -192,6 +192,23 @@ void TranslatorGLSL::writeExtensionBehavior(TIntermNode *root)
         sink << "#extension GL_ARB_explicit_attrib_location : require\n";
     }
 
+    // Need to enable gpu_shader5 to have index constant sampler array indexing
+    if (getOutputType() != SH_ESSL_OUTPUT && getOutputType() < SH_GLSL_400_CORE_OUTPUT)
+    {
+        sink << "#extension GL_ARB_gpu_shader5 : ";
+
+        // Don't use "require" on WebGL 1 to avoid breaking WebGL on drivers that silently
+        // support index constant sampler array indexing, but don't have the extension.
+        if (getShaderVersion() >= 300)
+        {
+            sink << "require\n";
+        }
+        else
+        {
+            sink << "enable\n";
+        }
+    }
+
     TExtensionGLSL extensionGLSL(getOutputType());
     root->traverse(&extensionGLSL);
 

src/libANGLE/renderer/gl/renderergl_utils.cpp

@@ -536,6 +536,17 @@ void GenerateCaps(const FunctionsGL *functions, gl::Caps *caps, gl::TextureCapsM
         LimitVersion(maxSupportedESVersion, gl::Version(2, 0));
     }
 
+    // Check if index constant sampler array indexing is supported
+    if (!functions->isAtLeastGL(gl::Version(4, 0)) &&
+        !functions->isAtLeastGLES(gl::Version(2, 0)) &&
+        !functions->hasExtension("GL_ARB_gpu_shader5"))
+    {
+        // This should also be required for ES2 but there are some driver support index constant
+        // sampler array indexing without meeting the requirements above. Don't limit their ES
+        // version as it would break WebGL for some users.
+        LimitVersion(maxSupportedESVersion, gl::Version(2, 0));
+    }
+
     // Check if sampler objects are supported
     if (!functions->isAtLeastGL(gl::Version(3, 3)) &&
         !functions->hasGLExtension("GL_ARB_sampler_objects") &&

src/tests/gl_tests/GLSLTest.cpp

@@ -1821,6 +1821,50 @@ TEST_P(GLSLTest_ES3, InitGlobalArrayWithArrayIndexing)
     EXPECT_NE(0u, program);
 }
 
+// Test that index-constant sampler array indexing is supported.
+TEST_P(GLSLTest, IndexConstantSamplerArrayIndexing)
+{
+    if (IsD3D11_FL93()) {
+        std::cout << "Test skipped on D3D11 FL 9.3." << std::endl;
+        return;
+    }
+
+    const std::string vertexShaderSource =
+        "attribute vec4 vPosition;\n"
+        "void main()\n"
+        "{\n"
+        "      gl_Position = vPosition;\n"
+        "}";
+
+    const std::string fragmentShaderSource =
+        "precision mediump float;\n"
+        "uniform sampler2D uni[2];\n"
+        "\n"
+        "float zero(int x)\n"
+        "{\n"
+        "    return float(x) - float(x);\n"
+        "}\n"
+        "\n"
+        "void main()\n"
+        "{\n"
+        "    vec4 c = vec4(0,0,0,0);\n"
+        "    for (int ii = 1; ii < 3; ++ii) {\n"
+        "        if (c.x > 255.0) {\n"
+        "            c.x = 255.0 + zero(ii);\n"
+        "            break;\n"
+        "        }\n"
+        // Index the sampler array with a predictable loop index (index-constant) as opposed to
+        // a true constant. This is valid in OpenGL ES but isn't in many Desktop OpenGL versions,
+        // without an extension.
+        "        c += texture2D(uni[ii - 1], vec2(0.5, 0.5));\n"
+        "    }\n"
+        "    gl_FragColor = c;\n"
+        "}";
+
+    GLuint program = CompileProgram(vertexShaderSource, fragmentShaderSource);
+    EXPECT_NE(0u, program);
+}
+
 // Use this to select which configurations (e.g. which renderer, which GLES major version) these tests should be run against.
 ANGLE_INSTANTIATE_TEST(GLSLTest,
                        ES2_D3D9(),