fix bug for querying sample positions on D3D

src/libANGLE/renderer/d3d/d3d11/renderer11_utils.cpp

@@ -1543,7 +1543,7 @@ void GenerateCaps(ID3D11Device *device,
 
 void GetSamplePosition(GLsizei sampleCount, size_t index, GLfloat *xy)
 {
-    size_t indexKey = static_cast<size_t>(ceil(log(sampleCount)));
+    size_t indexKey = static_cast<size_t>(ceil(log2(sampleCount)));
     ASSERT(indexKey < kSamplePositions.size() &&
            (2 * index + 1) < kSamplePositions[indexKey].size());
 

src/tests/gl_tests/TextureMultisampleTest.cpp

@@ -13,6 +13,19 @@ using namespace angle;
 
 namespace
 {
+// Sample positions of d3d standard pattern. Some of the sample positions might not the same as
+// opengl.
+using SamplePositionsArray                                            = std::array<float, 32>;
+static constexpr std::array<SamplePositionsArray, 5> kSamplePositions = {
+    {{{0.5f, 0.5f}},
+     {{0.75f, 0.75f, 0.25f, 0.25f}},
+     {{0.375f, 0.125f, 0.875f, 0.375f, 0.125f, 0.625f, 0.625f, 0.875f}},
+     {{0.5625f, 0.3125f, 0.4375f, 0.6875f, 0.8125f, 0.5625f, 0.3125f, 0.1875f, 0.1875f, 0.8125f,
+       0.0625f, 0.4375f, 0.6875f, 0.9375f, 0.9375f, 0.0625f}},
+     {{0.5625f, 0.5625f, 0.4375f, 0.3125f, 0.3125f, 0.625f,  0.75f,   0.4375f,
+       0.1875f, 0.375f,  0.625f,  0.8125f, 0.8125f, 0.6875f, 0.6875f, 0.1875f,
+       0.375f,  0.875f,  0.5f,    0.0625f, 0.25f,   0.125f,  0.125f,  0.75f,
+       0.0f,    0.5f,    0.9375f, 0.25f,   0.875f,  0.9375f, 0.0625f, 0.0f}}}};
 
 class TextureMultisampleTest : public ANGLETest
 {
@@ -170,6 +183,40 @@ TEST_P(TextureMultisampleTestES31, MaxDepthTextureSamples)
     EXPECT_NE(std::numeric_limits<GLint>::max(), maxDepthTextureSamples);
 }
 
+// The value of sample position should be equal to standard pattern on D3D.
+TEST_P(TextureMultisampleTestES31, CheckSamplePositions)
+{
+    ANGLE_SKIP_TEST_IF(!IsD3D11());
+
+    GLsizei maxSamples = 0;
+    glGetIntegerv(GL_MAX_SAMPLES, &maxSamples);
+
+    GLfloat samplePosition[2];
+
+    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, mFramebuffer);
+
+    for (int sampleCount = 1; sampleCount <= maxSamples; sampleCount++)
+    {
+        GLTexture texture;
+        size_t indexKey = static_cast<size_t>(ceil(log2(sampleCount)));
+        glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, texture);
+        glTexStorage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, sampleCount, GL_RGBA8, 1, 1, GL_TRUE);
+        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE,
+                               texture, 0);
+        EXPECT_GLENUM_EQ(GL_FRAMEBUFFER_COMPLETE, glCheckFramebufferStatus(GL_FRAMEBUFFER));
+        ASSERT_GL_NO_ERROR();
+
+        for (int sampleIndex = 0; sampleIndex < sampleCount; sampleIndex++)
+        {
+            glGetMultisamplefv(GL_SAMPLE_POSITION, sampleIndex, samplePosition);
+            EXPECT_EQ(samplePosition[0], kSamplePositions[indexKey][2 * sampleIndex]);
+            EXPECT_EQ(samplePosition[1], kSamplePositions[indexKey][2 * sampleIndex + 1]);
+        }
+    }
+
+    ASSERT_GL_NO_ERROR();
+}
+
 ANGLE_INSTANTIATE_TEST(TextureMultisampleTest,
                        ES31_D3D11(),
                        ES3_OPENGL(),