[Fix, Test] (MG_State, MG_Backend, MG_Impl, MG_Test): review wave - hand the mapping back instead of renewing it, retire an immutable ES store on respecify, and tag glTexStorage2D levels too

MobileGL/MG_IntegrationTest/Scenarios/VertexArrayEnableDisableScenario.cpp

@@ -77,8 +77,12 @@ namespace MGITest {
                 declarations += "in int a_" + std::to_string(i) + ";\n";
                 copies += "  sum += a_" + std::to_string(i) + ";\n";
             }
-            const std::string vertexSource = "#version 450\n\n" + declarations + "out int sum;\n\nvoid main()\n{\n" +
-                                             copies + "}\n";
+            // `flat` where the CTS case has none: an integral shader output cannot be
+            // interpolated, so a driver is within its rights to reject the unqualified form
+            // even with no matching fragment input. The capture reads the same value either
+            // way, and the qualifier keeps this scenario portable off llvmpipe.
+            const std::string vertexSource = "#version 450\n\n" + declarations +
+                                             "flat out int sum;\n\nvoid main()\n{\n" + copies + "}\n";
             const std::string fragmentSource = R"(#version 450
 
 out vec4 color;

MobileGL/MG_IntegrationTest/Scenarios/XfbCaptureBufferReuseScenario.cpp

@@ -27,6 +27,7 @@
 // rather than a parameter: it is the configuration that already worked, so it
 // has to keep working for the others to mean anything.
 
+#include <cmath>
 #include <cstdio>
 #include <cstring>
 #include <string>
@@ -157,7 +158,11 @@ void main() {
                 for (std::size_t i = 0; i < kCaptureFloats; ++i) {
                     const float expected = value + static_cast<float>(i);
                     const float got = data[i];
-                    if (got - expected > 0.01f || expected - got > 0.01f) {
+                    // isfinite first: every ordered comparison against a NaN is false, so a
+                    // pair of one-sided range tests REPORTS SUCCESS for uninitialised
+                    // storage that happens to read as NaN - which is exactly the failure
+                    // these scenarios exist to catch.
+                    if (!std::isfinite(got) || std::fabs(got - expected) > 0.01f) {
                         return ::testing::AssertionFailure()
                                << "component " << i << " is " << got << ", expected " << expected
                                << (got == kPoison ? " (the capture never reached these bytes)" : "");
@@ -281,7 +286,12 @@ void main() {
             GLuint xfbBuffer = 0;
             glGenBuffers(1, &xfbBuffer);
             glBindBuffer(GL_TRANSFORM_FEEDBACK_BUFFER, xfbBuffer);
-            glBufferStorage(GL_TRANSFORM_FEEDBACK_BUFFER, kCaptureBytes, nullptr, GL_MAP_READ_BIT);
+            // Poisoned at creation - the storage is immutable, so this is the only chance to
+            // put a recognisable value there, and without it a span that captured nothing
+            // would be indistinguishable from one that captured the right thing whenever the
+            // untouched bytes happened to read back as the expected number.
+            const std::vector<float> poison(kCaptureFloats, kPoison);
+            glBufferStorage(GL_TRANSFORM_FEEDBACK_BUFFER, kCaptureBytes, poison.data(), GL_MAP_READ_BIT);
             ASSERT_EQ(glGetError(), GL_NO_ERROR) << "glBufferStorage on the capture buffer";
             glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, xfbBuffer);