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[Test] (Integration): pin the adopted mesh-arena store - cross-frame SubData visibility, readback identity, and the GPU-written readback

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swung0x48
2026-08-28 04:19:11 -04:00
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MobileGL/MG_IntegrationTest/CMakeLists.txt
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@@ -113,6 +113,7 @@ add_executable(MobileGLIntegrationTest
Scenarios/LayeredAttachmentShapeScenario.cpp Scenarios/LayeredAttachmentShapeScenario.cpp
Scenarios/LayeredTextureReadbackScenario.cpp Scenarios/LayeredTextureReadbackScenario.cpp
Scenarios/AtomicCounterScenario.cpp Scenarios/AtomicCounterScenario.cpp
Scenarios/LargeArenaAdoptionScenario.cpp
Scenarios/SsboArrayDynamicIndexScenario.cpp Scenarios/SsboArrayDynamicIndexScenario.cpp
Scenarios/StorageBufferRegrowScenario.cpp Scenarios/StorageBufferRegrowScenario.cpp
Scenarios/SpirvShaderBinaryScenario.cpp Scenarios/SpirvShaderBinaryScenario.cpp
MobileGL/MG_IntegrationTest/Scenarios/LargeArenaAdoptionScenario.cpp
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// MobileGL - MobileGL/MG_IntegrationTest/Scenarios/LargeArenaAdoptionScenario.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
//
// Scenario - MESH-ARENA-SIZED BUFFERS, END TO END.
//
// A buffer store of at least 16MiB is adopted into the backend's persistently and
// coherently mapped GPU storage the moment it is defined (BufferObject::
// TryAdoptLargeStorage): the CPU shadow is dropped and every later write lands
// directly in GPU-visible memory with no per-write driver call. Minecraft 26.3
// streams chunk meshes into 128MB vertex arenas with plain glNamedBufferSubData -
// on Mali, every driver-mediated route for that write into a busy mutable store
// either parks the calling thread or ghost-copies the whole arena on a driver
// worker (~167ms per touched arena: the recurring in-world hiccup this adoption
// removed). Every existing buffer scenario uses stores far below the threshold,
// so without this file the adopted path would have zero coverage.
//
// What is pinned, deliberately through the same API mix Minecraft uses:
// * a glBufferSubData written AFTER the arena was drawn (in flight) reaches the
// next draw - the write-visibility contract adoption must not weaken;
// * GetBufferSubData reads back the latest CPU write - the shadow IS the map;
// * a compute-shader write through an SSBO binding of the same arena is read
// back - the GPU-written path for adopted stores (glFinish + direct read).
#include <array>
#include <cstring>
#include <string>
#include <vector>
#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 {
// Comfortably past the 16MiB adoption threshold, and the vertex payload sits
// deep inside the store so an implementation that quietly clamped or aliased
// the adopted range would miss it.
constexpr GLsizeiptr kArenaBytes = GLsizeiptr(24) * 1024 * 1024;
constexpr GLintptr kVertexOffset = GLintptr(20) * 1024 * 1024;
constexpr const char* kVertexSource = R"(#version 430 core
layout(location = 0) in vec2 a_pos;
layout(location = 1) in vec3 a_color;
out vec3 v_color;
void main() {
v_color = a_color;
gl_Position = vec4(a_pos, 0.0, 1.0);
}
)";
constexpr const char* kFragmentSource = R"(#version 430 core
in vec3 v_color;
out vec4 o_color;
void main() { o_color = vec4(v_color, 1.0); }
)";
constexpr const char* kMarkerComputeSource = R"(#version 430 core
layout(local_size_x = 1) in;
layout(std430, binding = 0) buffer Arena { uint word; };
void main() { word = 0xC0FFEEu; }
)";
struct Vertex {
float x, y;
float r, g, b;
};
// A full-viewport quad, colored uniformly so one center readback speaks for
// the whole draw.
std::vector<Vertex> QuadVertices(float r, float g, float b) {
return {
{-1.f, -1.f, r, g, b}, {1.f, -1.f, r, g, b}, {1.f, 1.f, r, g, b},
{-1.f, -1.f, r, g, b}, {1.f, 1.f, r, g, b}, {-1.f, 1.f, r, g, b},
};
}
class LargeArenaAdoptionScenario : public ScenarioTest {
protected:
void SetUp() override {
ScenarioTest::SetUp();
if (!Ready()) return;
m_program = LinkProgram(kVertexSource, kFragmentSource);
ASSERT_NE(m_program, 0u) << m_buildLog;
glGenVertexArrays(1, &m_vao);
glBindVertexArray(m_vao);
glGenBuffers(1, &m_arena);
glBindBuffer(GL_ARRAY_BUFFER, m_arena);
// The NULL-data definition is the adoption point (and Minecraft's
// arena-creation idiom).
glBufferData(GL_ARRAY_BUFFER, kArenaBytes, nullptr, GL_DYNAMIC_DRAW);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex),
reinterpret_cast<void*>(kVertexOffset));
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex),
reinterpret_cast<void*>(kVertexOffset + 2 * sizeof(float)));
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
}
void TearDown() override {
if (!Ready()) return;
glUseProgram(0);
glBindVertexArray(0);
if (m_vao != 0) glDeleteVertexArrays(1, &m_vao);
if (m_arena != 0) glDeleteBuffers(1, &m_arena);
if (m_program != 0) glDeleteProgram(m_program);
if (m_compute != 0) glDeleteProgram(m_compute);
m_vao = 0;
m_arena = 0;
m_program = 0;
m_compute = 0;
}
unsigned int CompileStage(GLenum stage, const char* source) {
const GLuint shader = glCreateShader(stage);
glShaderSource(shader, 1, &source, nullptr);
glCompileShader(shader);
GLint compiled = 0;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
if (compiled == GL_FALSE) {
char log[2048] = {};
glGetShaderInfoLog(shader, sizeof(log) - 1, nullptr, log);
m_buildLog = std::string("shader did not compile: ") + log;
glDeleteShader(shader);
return 0;
}
return shader;
}
unsigned int LinkProgram(const char* vs, const char* fs) {
const GLuint v = CompileStage(GL_VERTEX_SHADER, vs);
if (v == 0) return 0;
const GLuint f = CompileStage(GL_FRAGMENT_SHADER, fs);
if (f == 0) {
glDeleteShader(v);
return 0;
}
const GLuint program = glCreateProgram();
glAttachShader(program, v);
glAttachShader(program, f);
glLinkProgram(program);
glDeleteShader(v);
glDeleteShader(f);
GLint linked = 0;
glGetProgramiv(program, GL_LINK_STATUS, &linked);
if (linked == GL_FALSE) {
char log[2048] = {};
glGetProgramInfoLog(program, sizeof(log) - 1, nullptr, log);
m_buildLog = std::string("program did not link: ") + log;
glDeleteProgram(program);
return 0;
}
return program;
}
void UploadQuad(float r, float g, float b) {
const auto vertices = QuadVertices(r, g, b);
glBindBuffer(GL_ARRAY_BUFFER, m_arena);
glBufferSubData(GL_ARRAY_BUFFER, kVertexOffset,
GLsizeiptr(vertices.size() * sizeof(Vertex)), vertices.data());
}
void DrawQuad() {
glViewport(0, 0, Gl().Width(), Gl().Height());
glClearColor(0.f, 0.f, 0.f, 1.f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(m_program);
glBindVertexArray(m_vao);
glDrawArrays(GL_TRIANGLES, 0, 6);
}
std::array<unsigned char, 4> CenterPixel() {
std::array<unsigned char, 4> px = {0, 0, 0, 0};
glReadPixels(Gl().Width() / 2, Gl().Height() / 2, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE,
px.data());
return px;
}
unsigned int m_program = 0;
unsigned int m_compute = 0;
unsigned int m_vao = 0;
unsigned int m_arena = 0;
std::string m_buildLog;
};
} // namespace
// The Minecraft shape: the arena is drawn, the frame retires, and a
// glBufferSubData rewrites the SAME vertex bytes while the previous frame's
// draw may still be in flight. The next draw must show the NEW bytes.
TEST_F(LargeArenaAdoptionScenario, SubDataAfterAnInFlightDrawReachesTheNextDraw) {
if (!Ready() || IsSkipped()) return;
UploadQuad(1.f, 0.f, 0.f);
DrawQuad();
auto px = CenterPixel();
EXPECT_EQ(FirstGLError(), 0u);
EXPECT_GT(px[0], 200) << "the first draw from the adopted arena never landed";
EXPECT_LT(px[1], 50);
Gl().EndFrame();
UploadQuad(0.f, 1.f, 0.f);
DrawQuad();
px = CenterPixel();
EXPECT_EQ(FirstGLError(), 0u);
EXPECT_GT(px[1], 200) << "the cross-frame rewrite of the adopted arena did not reach the draw; "
"the old color means the write went to bytes the draw no longer reads";
EXPECT_LT(px[0], 50) << "the draw still shows the previous frame's bytes";
}
// The shadow IS the mapping: a readback straight after a CPU write must hand
// back exactly those bytes.
TEST_F(LargeArenaAdoptionScenario, ReadbackSeesTheLatestCpuWrite) {
if (!Ready() || IsSkipped()) return;
const auto vertices = QuadVertices(0.25f, 0.5f, 0.75f);
glBindBuffer(GL_ARRAY_BUFFER, m_arena);
glBufferSubData(GL_ARRAY_BUFFER, kVertexOffset,
GLsizeiptr(vertices.size() * sizeof(Vertex)), vertices.data());
std::vector<Vertex> read(vertices.size());
glGetBufferSubData(GL_ARRAY_BUFFER, kVertexOffset,
GLsizeiptr(read.size() * sizeof(Vertex)), read.data());
EXPECT_EQ(FirstGLError(), 0u);
EXPECT_EQ(0, std::memcmp(read.data(), vertices.data(), read.size() * sizeof(Vertex)))
<< "GetBufferSubData of the adopted arena returned different bytes than the SubData wrote";
}
// A GPU write through an SSBO binding of the adopted arena must be visible to
// a CPU readback - the path that waits out the GPU and reads the coherent
// mapping directly.
TEST_F(LargeArenaAdoptionScenario, GpuWriteIntoTheArenaIsReadBack) {
if (!Ready() || IsSkipped()) return;
GLint maxComputeStorageBlocks = 0;
glGetIntegerv(GL_MAX_COMPUTE_SHADER_STORAGE_BLOCKS, &maxComputeStorageBlocks);
if (maxComputeStorageBlocks < 1) {
GTEST_SKIP() << "no compute shader storage blocks on this driver";
}
const GLuint compute = CompileStage(GL_COMPUTE_SHADER, kMarkerComputeSource);
ASSERT_NE(compute, 0u) << m_buildLog;
m_compute = glCreateProgram();
glAttachShader(m_compute, compute);
glLinkProgram(m_compute);
glDeleteShader(compute);
GLint linked = 0;
glGetProgramiv(m_compute, GL_LINK_STATUS, &linked);
ASSERT_EQ(linked, GL_TRUE);
const unsigned int seed = 0u;
glBindBuffer(GL_ARRAY_BUFFER, m_arena);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(seed), &seed);
glBindBufferRange(GL_SHADER_STORAGE_BUFFER, 0, m_arena, 0, sizeof(unsigned int));
glUseProgram(m_compute);
glDispatchCompute(1, 1, 1);
glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT | GL_BUFFER_UPDATE_BARRIER_BIT);
unsigned int marker = 0;
glGetBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(marker), &marker);
EXPECT_EQ(FirstGLError(), 0u);
EXPECT_EQ(marker, 0xC0FFEEu)
<< "the compute write into the adopted arena did not reach the CPU readback";
}
} // namespace MGITest