[Fix, Test] (MG_State, MG_Impl, MG_IntegrationTest): a double uniform initializer no longer reads zero

MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp

@@ -850,7 +850,12 @@ namespace MobileGL::MG_Impl::GLImpl {
     // vector per column - while the value glGetUniform* must return is tightly packed
     // columns * rows floats. Only mat4 is the same either way; every other shape needs the
     // padding undone, and the readback has to undo exactly what UniformMatrixfv_Object put
-    // there. Returns false when `ttype` is not a float matrix (nothing to unpack).
+    // there. Returns false when there is nothing here to unpack.
+    //
+    // A DOUBLE matrix is declined not because it is laid out differently - it is not, the
+    // demotion makes a dmat4 a mat4 in the shader and a mat4-shaped slot here - but because it
+    // is ROUTED differently: the caller's component-by-component EbtDouble branch has to widen
+    // each float back to the queried type, and it undoes the same padding itself.
     Bool TryGatherFloatMatrixColumns(const glslang::TType* ttype, const char* pBase, void* params) {
         if (ttype == nullptr || !ttype->isMatrix() || ttype->getBasicType() == glslang::EbtDouble) return false;
         const Int columns = ttype->getMatrixCols();

MobileGL/MG_IntegrationTest/Scenarios/DoublePrecisionScenario.cpp

@@ -314,6 +314,45 @@ void main() {
             EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
         }
 
+        TEST_F(DoublePrecisionScenario, ADoubleUniformKeepsItsDeclaredInitializer) {
+            if (!Ready()) return;
+            // A declared initializer is seeded straight into the uniform shadow at link, and the
+            // seeding used to skip 64-bit floats outright ("no 32-bit shadow encoding") - which
+            // was true before the demotion and silently left every such uniform reading zero.
+            const char* source = R"(#version 430 core
+layout(local_size_x = 1) in;
+uniform double uSeeded = 2.5lf;
+uniform dvec3  uSeededVector = dvec3(4.0lf, 5.0lf, 6.0lf);
+layout(std430, binding = 0) buffer Output {
+    float g_out[];
+};
+void main() {
+    g_out[0] = float(uSeeded);
+    g_out[1] = float(uSeededVector.x);
+    g_out[2] = float(uSeededVector.y);
+    g_out[3] = float(uSeededVector.z);
+}
+)";
+            const GLuint program = CompileComputeProgram(source);
+            ASSERT_NE(program, 0u) << m_buildLog;
+
+            glUseProgram(program);
+            glDispatchCompute(1, 1, 1);
+            glMemoryBarrier(GL_BUFFER_UPDATE_BARRIER_BIT);
+            std::vector<float> values(4, -1.0f);
+            glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_output);
+            glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, 4 * sizeof(float), values.data());
+            glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
+            glUseProgram(0);
+            glDeleteProgram(program);
+
+            EXPECT_FLOAT_EQ(values[0], 2.5f) << "scalar double initializer";
+            EXPECT_FLOAT_EQ(values[1], 4.0f) << "dvec3 initializer .x";
+            EXPECT_FLOAT_EQ(values[2], 5.0f) << "dvec3 initializer .y";
+            EXPECT_FLOAT_EQ(values[3], 6.0f) << "dvec3 initializer .z";
+            EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
+        }
+
         TEST_F(DoublePrecisionScenario, TheFp64ExtensionIsNotAdvertised) {
             if (!Ready()) return;
             // The shader above compiled, linked and ran without the extension string, which is

MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp

@@ -165,10 +165,18 @@ namespace MobileGL::MG_State::GLState {
             const Int elements = init.arraySize;
             if (componentsPerElement <= 0 || elements <= 0) continue;
 
-            const Bool isFloat = init.basicType == glslang::EbtFloat || init.basicType == glslang::EbtFloat16;
+            // EbtDouble belongs with the floats now, not with the skipped types: every 64-bit
+            // float in a shader is narrowed to 32 bits before the module reaches a backend
+            // (ShaderTranspiler::DemoteFloat64Pass), so a `uniform double d = 1.5;` has exactly
+            // the 32-bit shadow encoding a `uniform float` does - and glslang already folded its
+            // value into floatValues, which is a vector<double> either way. Leaving it out meant
+            // the initializer was silently dropped and the uniform came up zero.
+            const Bool isFloat = init.basicType == glslang::EbtFloat ||
+                                 init.basicType == glslang::EbtFloat16 ||
+                                 init.basicType == glslang::EbtDouble;
             const Bool isInt = init.basicType == glslang::EbtInt || init.basicType == glslang::EbtUint ||
                                init.basicType == glslang::EbtBool;
-            // Anything else (fp64, 64-bit integers) has no 32-bit shadow encoding here, and a
+            // Anything else (64-bit integers) has no 32-bit shadow encoding here, and a
             // half-written uniform is worse than an untouched one.
             if (!isFloat && !isInt) continue;
             const SizeT provided = isFloat ? init.floatValues.size() : init.intValues.size();