Fix for readPixels() to PBO fast path.

src/libANGLE/renderer/vulkan/vk_helpers.cpp

@@ -6384,7 +6384,7 @@ angle::Result ImageHelper::readPixels(ContextVk *contextVk,
 
         VkBufferImageCopy region = {};
         region.bufferImageHeight = srcExtent.height;
-        region.bufferOffset      = packPixelsParams.offset;
+        region.bufferOffset      = packPixelsParams.offset + reinterpret_cast<ptrdiff_t>(pixels);
         region.bufferRowLength   = packPixelsParams.outputPitch / readFormat->pixelBytes;
         region.imageExtent       = srcExtent;
         region.imageOffset       = srcOffset;

src/tests/gl_tests/ReadPixelsTest.cpp

@@ -253,6 +253,42 @@ TEST_P(ReadPixelsPBONVTest, ReadFromFBO)
     EXPECT_GL_NO_ERROR();
 }
 
+// Test calling ReadPixels with a non-zero "data" param into a PBO
+TEST_P(ReadPixelsPBONVTest, ReadFromFBOWithDataOffset)
+{
+    ANGLE_SKIP_TEST_IF(!hasPBOExts() || !IsGLExtensionEnabled("GL_EXT_map_buffer_range") ||
+                       !IsGLExtensionEnabled("GL_OES_mapbuffer"));
+
+    glBindFramebuffer(GL_FRAMEBUFFER, mFBO);
+    glViewport(0, 0, mFBOWidth, mFBOHeight);
+    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT);
+    // Clear first pixel to green
+    glScissor(0, 0, 1, 1);
+    glEnable(GL_SCISSOR_TEST);
+    glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT);
+    EXPECT_GL_NO_ERROR();
+
+    glBindBuffer(GL_PIXEL_PACK_BUFFER, mPBO);
+
+    // Read (height - 1) rows offset by width * 4.
+    glReadPixels(0, 0, mFBOWidth, mFBOHeight - 1, GL_RGBA, GL_UNSIGNED_BYTE,
+                 reinterpret_cast<void *>(mFBOWidth * 4));
+
+    void *mappedPtr =
+        glMapBufferRangeEXT(GL_PIXEL_PACK_BUFFER, 0, 4 * mFBOWidth * mFBOHeight, GL_MAP_READ_BIT);
+    GLColor *dataColor = static_cast<GLColor *>(mappedPtr);
+    EXPECT_GL_NO_ERROR();
+
+    EXPECT_EQ(GLColor::green, dataColor[mFBOWidth]);
+    EXPECT_EQ(GLColor::red, dataColor[mFBOWidth + 1]);
+    EXPECT_EQ(GLColor::red, dataColor[mFBOWidth * mFBOHeight - 1]);
+
+    glUnmapBufferOES(GL_PIXEL_PACK_BUFFER);
+    EXPECT_GL_NO_ERROR();
+}
+
 class ReadPixelsPBOTest : public ReadPixelsPBONVTest
 {
   protected: