Add end2end test for readonly feedbackloop

src/tests/angle_end2end_tests.gni

@@ -101,6 +101,7 @@ angle_end2end_tests_sources = [
   "gl_tests/ProgramParameterTest.cpp",
   "gl_tests/ProgramPipelineTest.cpp",
   "gl_tests/ProvokingVertexTest.cpp",
+  "gl_tests/ReadOnlyFeedbackLoopTest.cpp",
   "gl_tests/ReadPixelsTest.cpp",
   "gl_tests/RenderbufferMultisampleTest.cpp",
   "gl_tests/RendererTest.cpp",

src/tests/gl_tests/ReadOnlyFeedbackLoopTest.cpp

+//
+// Copyright 2020 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+
+// Test that invokes a usecase where there is a feedback loop but the framebuffer
+// depth attachment is only read from
+
+#include "test_utils/ANGLETest.h"
+#include "test_utils/gl_raii.h"
+
+using namespace angle;
+
+class ReadOnlyFeedbackLoopTest : public ANGLETest
+{
+  protected:
+    ReadOnlyFeedbackLoopTest()
+    {
+        setWindowWidth(256);
+        setWindowHeight(256);
+        setConfigRedBits(8);
+        setConfigGreenBits(8);
+        setConfigBlueBits(8);
+        setConfigAlphaBits(8);
+    }
+
+    void testSetUp() override
+    {
+        glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+        glClearDepthf(1.0f);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+        glDepthRangef(-1.0f, 1.0f);
+
+        glEnable(GL_BLEND);
+        glDisable(GL_DEPTH_TEST);
+
+        ASSERT_GL_NO_ERROR();
+    }
+};
+
+// Fill out a depth texture to specific values and use it both as a sampler and a depth texture
+// with depth write disabled. This is to test a "read-only feedback loop" that needs to be
+// supported to match industry standard.
+TEST_P(ReadOnlyFeedbackLoopTest, DepthFeedbackLoop)
+{
+    // TODO - Add support for readonly feedback loops (http://anglebug.com/4778)
+    ANGLE_SKIP_TEST_IF(true);
+
+    const GLuint width  = getWindowWidth();
+    const GLuint height = getWindowHeight();
+
+    GLTexture colorTex;
+    GLTexture depthTex;
+    GLTexture finalTex;
+
+    GLFramebuffer gbufferFbo;
+    GLFramebuffer finalFbo;
+
+    ANGLE_GL_PROGRAM(colorFillProgram, essl1_shaders::vs::Simple(), essl1_shaders::fs::Red());
+    ANGLE_GL_PROGRAM(textureFillProgram, essl1_shaders::vs::Texture2D(),
+                     essl1_shaders::fs::Texture2D());
+
+    glBindTexture(GL_TEXTURE_2D, colorTex);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    EXPECT_GL_NO_ERROR();
+
+    glBindTexture(GL_TEXTURE_2D, depthTex);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, width, height, 0, GL_DEPTH_COMPONENT,
+                 GL_UNSIGNED_INT, nullptr);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    EXPECT_GL_NO_ERROR();
+
+    glBindFramebuffer(GL_FRAMEBUFFER, gbufferFbo);
+    EXPECT_GL_NO_ERROR();
+
+    // Attach a color and depth texture to the FBO
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, colorTex, 0);
+    EXPECT_GL_NO_ERROR();
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthTex, 0);
+    EXPECT_GL_NO_ERROR();
+
+    ASSERT_GLENUM_EQ(GL_FRAMEBUFFER_COMPLETE, glCheckFramebufferStatus(GL_FRAMEBUFFER));
+
+    // Set the color texture to blue and depth texture to 1.0f
+    glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
+    glClearDepthf(1.0f);
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+    ASSERT_GL_NO_ERROR();
+
+    // Enable Depth test with passing always to write depth.
+    glEnable(GL_DEPTH_TEST);
+    glDepthMask(GL_TRUE);
+    glDepthFunc(GL_ALWAYS);
+
+    // Fill the middle of the depth texture with 0.0f. while the border remains 1.0f as
+    // previously cleared.
+    const GLfloat depthValue = 0.0f;
+    drawQuad(colorFillProgram, essl1_shaders::PositionAttrib(), depthValue, 0.6f);
+
+    EXPECT_GL_NO_ERROR();
+
+    glBindTexture(GL_TEXTURE_2D, finalTex);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    EXPECT_GL_NO_ERROR();
+
+    glBindFramebuffer(GL_FRAMEBUFFER, finalFbo);
+    EXPECT_GL_NO_ERROR();
+
+    // Enable Depth test without depth write.
+    glEnable(GL_DEPTH_TEST);
+    glDepthMask(GL_FALSE);
+    glDepthFunc(GL_GREATER);
+
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, finalTex, 0);
+    EXPECT_GL_NO_ERROR();
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthTex, 0);
+    EXPECT_GL_NO_ERROR();
+    ASSERT_GLENUM_EQ(GL_FRAMEBUFFER_COMPLETE, glCheckFramebufferStatus(GL_FRAMEBUFFER));
+
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+    glBindTexture(GL_TEXTURE_2D, depthTex);
+
+    // Fill finalTex with values read from depthTex. This should work even though depthTex
+    // is also bound as the depth attachment, because depth write is disabled.
+    // The write to finalTex only succeeds for the middle region due to depth test.
+    drawQuad(textureFillProgram, essl1_shaders::PositionAttrib(), 0.7f, 1.0f);
+
+    // Copy finalTex to default framebuffer for verification. Depth values written in the first
+    // draw call are expected in the middle, while the clear value in the clear before the
+    // second draw call are expected at the border.
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glDisable(GL_DEPTH_TEST);
+    glDepthMask(GL_FALSE);
+    glBindTexture(GL_TEXTURE_2D, finalTex);
+    drawQuad(textureFillProgram, essl1_shaders::PositionAttrib(), 0.0f, 1.0f);
+    EXPECT_GL_NO_ERROR();
+
+    GLint depthColorValue = (depthValue)*128 + 128;
+    EXPECT_EQ(depthColorValue, angle::ReadColor(width / 2, height / 2).R);
+    EXPECT_PIXEL_EQ(0, 0, 0, 0, 255, 255);
+}
+
+// Instantiate the test for ES2 and ES3.
+ANGLE_INSTANTIATE_TEST_ES2_AND_ES3(ReadOnlyFeedbackLoopTest);