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MobileGL/MobileGL/MG_IntegrationTest/Scenarios/SampleMaskScopeScenario.cpp
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// MobileGL - MobileGL/MG_IntegrationTest/Scenarios/SampleMaskScopeScenario.cpp
// Copyright (c) 2026 MobileGL-Dev
// Licensed under the GNU Lesser General Public License v3.0:
// https://www.gnu.org/licenses/gpl-3.0.txt
// https://www.gnu.org/licenses/lgpl-3.0.txt
// SPDX-License-Identifier: LGPL-3.0-only
// End of Source File Header
//
// Scenario - GL_SAMPLE_MASK IS A MULTISAMPLE FRAGMENT OPERATION, SO IT DOES NOTHING AT ONE SAMPLE.
//
// GL 4.6 core 17.3.3 groups alpha-to-coverage, sample coverage and the sample mask together and
// says they make no change "if MULTISAMPLE is disabled, or if the value of SAMPLE_BUFFERS is not
// one". SAMPLE_BUFFERS is 0 for a single-sample framebuffer, so on one the mask is inert whatever
// glSampleMaski last wrote.
//
// Vulkan has no such rule. VkPipelineMultisampleStateCreateInfo::pSampleMask is ANDed with
// rasterization coverage at every rasterizationSamples, and at one sample that coverage is bit 0
// alone - so a mask with bit 0 clear discards every fragment of every primitive. Plumbing
// glSampleMaski straight into pSampleMask therefore turned an ordinary and legal GL sequence into
// a fully black draw:
//
// glEnable(GL_SAMPLE_MASK); glSampleMaski(0, 0x2); // while an MSAA target is bound
// ... render ...
// glBindFramebuffer(GL_FRAMEBUFFER, 0); draw a fullscreen quad to present
//
// Neither piece of state is per-framebuffer, so nothing resets it when the target changes, and
// dEQP/GL-CTS multisample cases leave exactly these masks behind. That is the MSAA-then-present
// shape every application uses.
//
// The cases below are single-sample by construction (the scenario harness's colour FBO), so each
// one asserts that the mask changed nothing.
#include <string>
#include "../Harness/HeadlessGL.h"
#include "../Harness/ScenarioFixture.h"
#ifdef GLAPI
#undef GLAPI
#endif
#define GL_GLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GL/glcorearb.h>
#undef GL_GLEXT_PROTOTYPES
namespace MGITest {
namespace {
constexpr int kFboSize = 32;
constexpr const char* kQuadVertexSource = R"(#version 430 core
void main() {
vec2 corner = vec2((gl_VertexID & 1) == 0 ? -1.0 : 1.0,
(gl_VertexID & 2) == 0 ? -1.0 : 1.0);
gl_Position = vec4(corner, 0.0, 1.0);
}
)";
constexpr const char* kGreenFragmentSource = R"(#version 430 core
out vec4 o_color;
void main() {
o_color = vec4(0.0, 1.0, 0.0, 1.0);
}
)";
class SampleMaskScopeScenario : public ScenarioTest {
protected:
void SetUp() override {
ScenarioTest::SetUp();
if (!Ready()) return;
m_target = MakeColorFbo(kFboSize, kFboSize);
ASSERT_NE(m_target.fbo, 0u) << "could not create the render target";
glGenVertexArrays(1, &m_vao);
std::string error;
m_program = CompileProgram(kQuadVertexSource, kGreenFragmentSource, &error);
ASSERT_NE(m_program, 0u) << error;
}
void TearDown() override {
if (!Ready()) return;
// Process-wide GL state: leaving it set would hand the next scenario in this
// process the very bug under test.
glDisable(GL_SAMPLE_MASK);
glSampleMaski(0, 0xFFFFFFFFu);
glBindVertexArray(0);
glUseProgram(0);
if (m_program != 0) glDeleteProgram(m_program);
if (m_vao != 0) glDeleteVertexArrays(1, &m_vao);
DestroyColorFbo(m_target);
ScenarioTest::TearDown();
}
void ExpectQuadStillPaints(const char* what) {
BindFbo(m_target);
ClearTo(0.0f, 0.0f, 0.0f, 1.0f);
glBindVertexArray(m_vao);
glUseProgram(m_program);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glBindVertexArray(0);
EXPECT_EQ(FirstGLError(), 0u) << what << ": the draw raised a GL error";
const Image image = ReadPixels(kFboSize, kFboSize);
ASSERT_FALSE(image.Empty()) << what << ": the readback came back empty";
EXPECT_TRUE(RegionIsMostly(image, 0, kFboSize - 1, 0, kFboSize - 1, "green", 0.0, what))
<< what << ": an all-black target means the sample mask discarded every fragment, "
<< "which GL says it cannot do on a single-sample framebuffer";
}
ColorFbo m_target{};
GLuint m_vao = 0;
unsigned int m_program = 0;
};
} // namespace
// The exact reported shape: bit 0 clear, so the single sample of a single-sample target is
// masked off if the mask is applied at all.
TEST_F(SampleMaskScopeScenario, AMaskWithBitZeroClearDoesNotDiscardASingleSampleDraw) {
if (!Ready() || IsSkipped()) return;
glEnable(GL_SAMPLE_MASK);
glSampleMaski(0, 0x2);
ASSERT_EQ(FirstGLError(), 0u) << "setting the sample mask raised a GL error";
ExpectQuadStillPaints("GL_SAMPLE_MASK enabled with mask 0x2");
}
// Zero is the strongest form of the same thing, and the mask value the CTS's mask_zero cases
// set.
TEST_F(SampleMaskScopeScenario, AZeroMaskDoesNotDiscardASingleSampleDraw) {
if (!Ready() || IsSkipped()) return;
glEnable(GL_SAMPLE_MASK);
glSampleMaski(0, 0x0);
ASSERT_EQ(FirstGLError(), 0u) << "setting the sample mask raised a GL error";
ExpectQuadStillPaints("GL_SAMPLE_MASK enabled with mask 0");
}
// Control: the same mask word with the capability disabled has never had any effect, so this
// one passed before the fix too. It is here so a regression that ignores the enable bit
// instead of the sample count is still caught.
TEST_F(SampleMaskScopeScenario, ADisabledSampleMaskDoesNotDiscardASingleSampleDraw) {
if (!Ready() || IsSkipped()) return;
glDisable(GL_SAMPLE_MASK);
glSampleMaski(0, 0x0);
ASSERT_EQ(FirstGLError(), 0u) << "setting the sample mask raised a GL error";
ExpectQuadStillPaints("GL_SAMPLE_MASK disabled with mask 0");
}
// The mask is state, not a draw parameter, so a second draw after the first must not inherit
// a pipeline built while the memo word and the payload disagreed. Two draws either side of a
// mask change, both to the same single-sample target, both required to paint.
TEST_F(SampleMaskScopeScenario, ChangingTheMaskBetweenSingleSampleDrawsKeepsBothPainting) {
if (!Ready() || IsSkipped()) return;
glEnable(GL_SAMPLE_MASK);
glSampleMaski(0, 0xFFFFFFFFu);
ExpectQuadStillPaints("first draw, full mask");
glSampleMaski(0, 0x2);
ASSERT_EQ(FirstGLError(), 0u) << "changing the sample mask raised a GL error";
ExpectQuadStillPaints("second draw, mask 0x2");
}
// GL_MAX_SAMPLE_MASK_WORDS must be 1 on both backends: MobileGL stores one word and
// SampleMaski_State raises GL_INVALID_VALUE for any maskNumber above 0, so advertising more
// makes dEQP's per-case gluStateReset - which issues glSampleMaski up to the advertised count
// - fail every case. DirectGLES clamped; DirectVulkan forwarded the raw device limit.
TEST_F(SampleMaskScopeScenario, TheAdvertisedSampleMaskWordCountMatchesWhatSampleMaskiAccepts) {
if (!Ready() || IsSkipped()) return;
GLint words = 0;
glGetIntegerv(GL_MAX_SAMPLE_MASK_WORDS, &words);
ASSERT_EQ(FirstGLError(), 0u) << "querying GL_MAX_SAMPLE_MASK_WORDS raised a GL error";
EXPECT_EQ(words, 1) << "every word below the advertised count must be writable, and only word 0 is";
for (GLint word = 0; word < words; ++word) {
glSampleMaski(static_cast<GLuint>(word), 0xFFFFFFFFu);
EXPECT_EQ(FirstGLError(), 0u) << "glSampleMaski(" << word << ", ...) was refused although "
<< "GL_MAX_SAMPLE_MASK_WORDS advertises " << words << " words";
}
}
} // namespace MGITest