Created attachment 144822 [details]
test case binary

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Issue analyze:
Take case “MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd” as an example. 

Summary of this case:
1),  Preset the depth buffer with value 0.5f, name it Zb, buffer depth
kClearDepth        = 0.5f;
glClearDepthf(kClearDepth);
2),  Draw quad with depth of 0.0f, name it Zf, fragment depth
drawQuad(depthTestProgram, essl1_shaders::PositionAttrib(), maskDepth ? 1.0f : 0.0f);

In theory, the depth 0.5f of glClearDepthf equals(GL_EQUAL) the depth of drawQuad 0.0f. There is an equation between these two depths:
Zb = 0.5 x Zf + 0.5

On NVidia’s platform, we observed what we expected. On Intel platform, didn’t.

I also did below tests with different buffer depth and different depth func (GL_GREATER and GL_LESS), you can easily see the relationship between Zf (0.0) and Zb(0.5) on Intel platform(You may also refer to attachment zbzf_testdata.png):
Zb	Zf  > (GL_GREATER)	< (GL_LESS)
0.5	0.0  	√	x
0.499	0.0  	√	x
0.501	0.0  	x	√


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Reproduce steps (You may try the attached binary to reproduce):
1. Download angle source and install deps:
(https://github.com/google/angle/blob/master/doc/DevSetup.md)
git clone https://chromium.googlesource.com/angle/angle
cd angle
python scripts/bootstrap.py
gclient sync
git checkout master
./build/install-build-deps.sh
gn gen out/Release

2. Edit code(To enable the skipped test case)
--- a/src/tests/gl_tests/ClearTest.cpp
+++ b/src/tests/gl_tests/ClearTest.cpp
@@ -1248,7 +1248,7 @@ void MaskedScissoredClearTestBase::MaskedScissoredColorDepthStencilClear(
                                                   &maskColor, &maskDepth, &maskStencil, &scissor);

     // clearDepth && !maskDepth fails on Intel Ubuntu 19.04 Mesa 19.0.2 GL. http://anglebug.com/3614
-    ANGLE_SKIP_TEST_IF(IsLinux() && IsIntel() && IsDesktopOpenGL() && clearDepth && !maskDepth);
+    // ANGLE_SKIP_TEST_IF(IsLinux() && IsIntel() && IsDesktopOpenGL() && clearDepth && !maskDepth);


3. Build
ninja -C out/Release


4.  Run test case
./out/Release/angle_end2end_tests --gtest_filter=MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd


I have reproduced this issue on below platform:
Mesa 19.1.1/Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)/Ubuntu 18.04

I can not reproduce this on:
OpenGL version string: 4.6.0 NVIDIA 430.26/GeForce GTX 1060/Ubuntu 18.04.
Windows 10/Intel UHD 630/



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The failed logs on Intel:
[----------] 1 test from MaskedScissoredClearTest
[ RUN  	] MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd
../../src/tests/gl_tests/ClearTest.cpp:1355: Failure
The difference between (expectedCenterColorRGB.R) and pixel[0] is 51, which exceeds 1, where
(expectedCenterColorRGB.R) evaluates to 0,
pixel[0] evaluates to 51, and
1 evaluates to 1.
../../src/tests/gl_tests/ClearTest.cpp:1355: Failure
The difference between (expectedCenterColorRGB.G) and pixel[1] is 102, which exceeds 1, where
(expectedCenterColorRGB.G) evaluates to 0,
pixel[1] evaluates to 102, and
1 evaluates to 1.
…
…
...
1 evaluates to 1.
[  FAILED  ] MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd, where GetParam() = (ES2_OpenGL, 1, 1, 0, false) (38 ms)
[----------] 1 test from MaskedScissoredClearTest (38 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (38 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd, where GetParam() = (ES2_OpenGL, 1, 1, 0, false)

 1 FAILED TEST


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The pass logs on NV:

[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from MaskedScissoredClearTest
[ RUN  	] MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd
[   	OK ] MaskedScissoredClearTest.Test/ES2_OpenGL_clear_cd (90 ms)
[----------] 1 test from MaskedScissoredClearTest (90 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (90 ms total)
[  PASSED  ] 1 test.