Allow rendering to unused levels of bound Textures.

src/libANGLE/Framebuffer.cpp

@@ -262,6 +262,28 @@ angle::Result InitAttachment(const Context *context, FramebufferAttachment *atta
     }
     return angle::Result::Continue;
 }
+
+bool AttachmentOverlapsWithTexture(const FramebufferAttachment &attachment,
+                                   const Texture *texture,
+                                   const Sampler *sampler)
+{
+    if (!attachment.isTextureWithId(texture->id()))
+    {
+        return false;
+    }
+
+    const gl::ImageIndex &index = attachment.getTextureImageIndex();
+    GLuint attachmentLevel      = static_cast<GLuint>(index.getLevelIndex());
+    GLuint textureBaseLevel     = texture->getBaseLevel();
+    GLuint textureMaxLevel      = textureBaseLevel;
+    if ((sampler && IsMipmapFiltered(sampler->getSamplerState())) ||
+        IsMipmapFiltered(texture->getSamplerState()))
+    {
+        textureMaxLevel = texture->getMipmapMaxLevel();
+    }
+
+    return attachmentLevel >= textureBaseLevel && attachmentLevel <= textureMaxLevel;
+}
 }  // anonymous namespace
 
 // This constructor is only used for default framebuffers.
@@ -1920,9 +1942,25 @@ bool Framebuffer::formsRenderingFeedbackLoopWith(const Context *context) const
         if (texture && texture->isSamplerComplete(context, sampler) &&
             texture->isBoundToFramebuffer(mState.mFramebufferSerial))
         {
-            // TODO(jmadill): Subresource check. http://anglebug.com/4500
+            // Check for level overlap.
+            for (const FramebufferAttachment &attachment : mState.mColorAttachments)
+            {
+                if (AttachmentOverlapsWithTexture(attachment, texture, sampler))
+                {
+                    return true;
+                }
+            }
+
+            if (AttachmentOverlapsWithTexture(mState.mDepthAttachment, texture, sampler))
+            {
                 return true;
             }
+
+            if (AttachmentOverlapsWithTexture(mState.mStencilAttachment, texture, sampler))
+            {
+                return true;
+            }
+        }
     }
 
     return false;

src/tests/gl_tests/WebGLCompatibilityTest.cpp

@@ -5077,6 +5077,53 @@ TEST_P(WebGLCompatibilityTest, DrawWithNoProgram)
     EXPECT_GL_ERROR(GL_INVALID_OPERATION);
 }
 
+// Ensures that rendering to different texture levels of a sampled texture is supported.
+TEST_P(WebGL2CompatibilityTest, RenderToLevelsOfSampledTexture)
+{
+    // TODO: Fix on Vulkan back-end. http://anglebug.com/4690
+    ANGLE_SKIP_TEST_IF(IsVulkan());
+
+    constexpr GLsizei kTexSize   = 2;
+    constexpr GLsizei kTexLevels = 2;
+
+    std::vector<GLColor> texData(kTexSize * kTexSize, GLColor::green);
+
+    GLTexture sourceTexture;
+    glBindTexture(GL_TEXTURE_2D, sourceTexture);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexStorage2D(GL_TEXTURE_2D, kTexLevels, GL_RGBA8, kTexSize, kTexSize);
+    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, kTexSize, kTexSize, GL_RGBA, GL_UNSIGNED_BYTE,
+                    texData.data());
+
+    GLFramebuffer fbo;
+    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, sourceTexture, 1);
+    ASSERT_GL_FRAMEBUFFER_COMPLETE(GL_FRAMEBUFFER);
+    glViewport(0, 0, kTexSize / 2, kTexSize / 2);
+
+    ANGLE_GL_PROGRAM(program, essl1_shaders::vs::Texture2D(), essl1_shaders::fs::Texture2D());
+    ASSERT_GL_NO_ERROR();
+
+    // Should work - drawing from level 0 to level 1.
+    drawQuad(program, essl1_shaders::PositionAttrib(), 0.5f, 1.0f, true);
+    EXPECT_GL_NO_ERROR();
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::green);
+
+    // Should not work - drawing from levels [0,1] to level 1.
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
+    drawQuad(program, essl1_shaders::PositionAttrib(), 0.5f, 1.0f, true);
+    EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+
+    // Should work - drawing with levels [0,1] to default FBO.
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glViewport(0, 0, getWindowWidth(), getWindowHeight());
+
+    drawQuad(program, essl1_shaders::PositionAttrib(), 0.5f, 1.0f, true);
+    EXPECT_GL_NO_ERROR();
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::green);
+}
+
 // Use this to select which configurations (e.g. which renderer, which GLES major version) these
 // tests should be run against.
 ANGLE_INSTANTIATE_TEST_ES2_AND_ES3(WebGLCompatibilityTest);