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MobileGL/MobileGL/MG_IntegrationTest/Scenarios/TextureUnitSamplingScenario.cpp
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// MobileGL - MobileGL/MG_IntegrationTest/Scenarios/TextureUnitSamplingScenario.cpp
// Copyright (c) 2025-2026 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
//
// P13 W6: WHAT A DRAW SAMPLES FROM A TEXTURE UNIT, ON A REAL CONTEXT. Two GL 4.6 rules that were
// pinned by DirectGLESSanity unit cases driving the monolith frontend arm's unit walk
// (BindCurrentTextures over the frontend's binding slots). That arm is gone - every library walks
// the units by handle now - so the rules are asserted here, through the whole pipe, on both
// backends and every arm the scenarios run on:
//
// * A multisample texture is fetched, never filtered, so the mip-chain completeness rules do
// not apply to it (GL 4.6 8.17) even though its MIN_FILTER keeps the initial
// NEAREST_MIPMAP_LINEAR. Calling it incomplete leaves the unit unbound, and every texelFetch
// reads zero from a texture that was written correctly (KHR-GL43.compute_shader.resource-
// texture's shape: clear through an FBO, then read through sampler2DMS).
// * Binding texture 0 to a unit samples the unit's default texture, which has no image and is
// therefore incomplete: (0, 0, 0, 1) (GL 4.6 8.17.1). The texture bound there before must not
// keep answering.
#include <array>
#include <cstdint>
#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 GLsizei kEdge = 4;
constexpr const char* kVertexSource = R"(#version 330 core
void main() {
vec2 corner = vec2((gl_VertexID << 1) & 2, gl_VertexID & 2);
gl_Position = vec4(corner * 2.0 - 1.0, 0.0, 1.0);
}
)";
constexpr const char* kFetchMultisampleSource = R"(#version 330 core
uniform sampler2DMS u_texture;
out vec4 o_color;
void main() { o_color = texelFetch(u_texture, ivec2(gl_FragCoord.xy), 0); }
)";
constexpr const char* kSample2DSource = R"(#version 330 core
uniform sampler2D u_texture;
out vec4 o_color;
void main() { o_color = texture(u_texture, vec2(0.5, 0.5)); }
)";
class TextureUnitSamplingScenario : public ScenarioTest {
protected:
void SetUp() override {
ScenarioTest::SetUp();
if (!Ready()) return;
DrainErrors();
glGenVertexArrays(1, &m_vao);
glBindVertexArray(m_vao);
glGenTextures(1, &m_target);
glBindTexture(GL_TEXTURE_2D, m_target);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, kEdge, kEdge);
glBindTexture(GL_TEXTURE_2D, 0);
glGenFramebuffers(1, &m_fbo);
glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_target, 0);
glViewport(0, 0, kEdge, kEdge);
glDisable(GL_SCISSOR_TEST);
glDisable(GL_BLEND);
glDisable(GL_DEPTH_TEST);
glPixelStorei(GL_PACK_ALIGNMENT, 4);
}
void TearDown() override {
if (!Ready()) return;
glUseProgram(0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
if (m_fbo != 0) glDeleteFramebuffers(1, &m_fbo);
if (m_msFbo != 0) glDeleteFramebuffers(1, &m_msFbo);
if (m_target != 0) glDeleteTextures(1, &m_target);
if (m_source != 0) glDeleteTextures(1, &m_source);
if (m_program != 0) glDeleteProgram(m_program);
if (m_vao != 0) glDeleteVertexArrays(1, &m_vao);
DrainErrors();
ScenarioTest::TearDown();
}
static void DrainErrors() {
for (int i = 0; i < 16 && glGetError() != GL_NO_ERROR; ++i) {
}
}
static GLuint Compile(GLenum stage, const char* source) {
const GLuint shader = glCreateShader(stage);
glShaderSource(shader, 1, &source, nullptr);
glCompileShader(shader);
GLint ok = GL_FALSE;
glGetShaderiv(shader, GL_COMPILE_STATUS, &ok);
if (ok != GL_TRUE) {
char log[1024] = {};
glGetShaderInfoLog(shader, sizeof(log), nullptr, log);
ADD_FAILURE() << "shader compile failed: " << log;
}
return shader;
}
void UseProgram(const char* fragmentSource) {
const GLuint vs = Compile(GL_VERTEX_SHADER, kVertexSource);
const GLuint fs = Compile(GL_FRAGMENT_SHADER, fragmentSource);
m_program = glCreateProgram();
glAttachShader(m_program, vs);
glAttachShader(m_program, fs);
glLinkProgram(m_program);
glDeleteShader(vs);
glDeleteShader(fs);
GLint ok = GL_FALSE;
glGetProgramiv(m_program, GL_LINK_STATUS, &ok);
ASSERT_EQ(ok, GL_TRUE) << "program link failed";
glUseProgram(m_program);
glUniform1i(glGetUniformLocation(m_program, "u_texture"), 0);
}
std::array<GLubyte, 4> DrawAndReadCentre() {
glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
glClearColor(0.5f, 0.5f, 0.5f, 0.5f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
std::array<GLubyte, 4> texel{};
glReadPixels(kEdge / 2, kEdge / 2, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, texel.data());
return texel;
}
GLuint m_vao = 0;
GLuint m_fbo = 0;
GLuint m_msFbo = 0;
GLuint m_target = 0;
GLuint m_source = 0;
GLuint m_program = 0;
};
TEST_F(TextureUnitSamplingScenario, AMultisampleTextureIsFetchedDespiteItsDefaultMipmapFilter) {
if (!Ready()) return;
glGenTextures(1, &m_source);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, m_source);
glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, 4, GL_RGBA8, kEdge, kEdge, GL_FALSE);
GLint minFilter = 0;
glGetTexParameteriv(GL_TEXTURE_2D_MULTISAMPLE, GL_TEXTURE_MIN_FILTER, &minFilter);
ASSERT_EQ(minFilter, GL_NEAREST_MIPMAP_LINEAR)
<< "the fixture is stale: the initial MIN_FILTER no longer asks for mipmaps";
glGenFramebuffers(1, &m_msFbo);
glBindFramebuffer(GL_FRAMEBUFFER, m_msFbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, m_source, 0);
ASSERT_EQ(glCheckFramebufferStatus(GL_FRAMEBUFFER), static_cast<GLenum>(GL_FRAMEBUFFER_COMPLETE));
glClearColor(1.0f, 0.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
ASSERT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR)) << "clearing the multisample texture failed";
UseProgram(kFetchMultisampleSource);
if (HasFatalFailure()) return;
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, m_source);
const auto texel = DrawAndReadCentre();
EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
EXPECT_EQ(static_cast<int>(texel[0]), 255) << "red: the multisample texture was not bound";
EXPECT_EQ(static_cast<int>(texel[1]), 0);
EXPECT_EQ(static_cast<int>(texel[2]), 255) << "blue: the multisample texture was not bound";
EXPECT_EQ(static_cast<int>(texel[3]), 255);
Gl().EndFrame();
}
TEST_F(TextureUnitSamplingScenario, BindingZeroSamplesTheIncompleteDefaultTexture) {
if (!Ready()) return;
glGenTextures(1, &m_source);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_source);
const GLubyte red[4] = {255, 0, 0, 255};
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, red);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
UseProgram(kSample2DSource);
if (HasFatalFailure()) return;
const auto bound = DrawAndReadCentre();
ASSERT_EQ(static_cast<int>(bound[0]), 255) << "the control: the bound texture is sampled";
ASSERT_EQ(static_cast<int>(bound[1]), 0);
glBindTexture(GL_TEXTURE_2D, 0);
const auto unbound = DrawAndReadCentre();
EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
EXPECT_EQ(static_cast<int>(unbound[0]), 0)
<< "texture 0 is bound, yet the unit still answers with the texture bound before it";
EXPECT_EQ(static_cast<int>(unbound[1]), 0);
EXPECT_EQ(static_cast<int>(unbound[2]), 0);
EXPECT_EQ(static_cast<int>(unbound[3]), 255) << "an incomplete texture samples as (0, 0, 0, 1)";
Gl().EndFrame();
}
} // namespace
} // namespace MGITest
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