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MobileGL/MobileGL/MG_IntegrationTest/Scenarios/PackBufferReadbackScenario.cpp
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// MobileGL - MobileGL/MG_IntegrationTest/Scenarios/PackBufferReadbackScenario.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
//
// P9 (W1, docs/archive/contracts/CONTRACT-P9.md §1): READS INTO A PIXEL PACK BUFFER ARE ANSWERED BY NOTHING.
//
// Under a transport a glReadPixels / glGetTexImage whose destination is a bound
// GL_PIXEL_PACK_BUFFER no longer waits for its pixels: it crosses as read_pixels_to_buffer /
// get_texture_image_to_buffer, the server lands the rows in the buffer at the client's PACK
// layout, and the client marks the buffer GPU-written so that the next CPU read of it - a
// glGetBufferSubData, a glMapBufferRange, or a texture upload that uses it as the UNPACK source -
// fetches the bytes through resource_readback.
//
// THE CASES ARE ORDINARY GL AND RUN ON THE MONOLITH ARMS TOO. Each one compares the pack buffer
// against the same read into client memory under the same pack state, both destinations
// pre-filled with the same byte, so the padding the pack state skips has to survive as well: the
// monolith and every split arm must agree with themselves, and therefore with each other. The
// one exception is the last case, which is about the WIRE (the read posted no reply and marked
// the buffer) and skips where there is no wire to ask.
//
// Every image is POSITION-DEPENDENT, so a row landed at the wrong stride, a band at the wrong
// offset or a byte swapped the wrong way cannot look right.
#include <array>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <string>
#include <vector>
#include "../Harness/HeadlessGL.h"
#include "../Harness/ScenarioFixture.h"
#include "../Harness/SplitRuntimePeek.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 GLubyte kFill = 0xAB;
// A texel that names its own position (and its layer), so nothing misplaced can match.
std::array<GLubyte, 4> PatternRgba8(int x, int y, int layer) {
return {static_cast<GLubyte>(x * 7 + layer * 31), static_cast<GLubyte>(y * 11 + layer),
static_cast<GLubyte>((x ^ y) + layer * 5), static_cast<GLubyte>(0x80 | (x + y))};
}
// Integers below 2^24 in every component, so float storage is exact and a byte swap of
// any of them is visibly different from the value.
std::array<GLfloat, 4> PatternRgba32f(int x, int y) {
return {static_cast<GLfloat>(x + 1), static_cast<GLfloat>(y + 3),
static_cast<GLfloat>(x * 64 + y), static_cast<GLfloat>(1000 + x * y)};
}
struct PackState {
const char* name;
GLint alignment;
GLint rowLength;
GLint skipPixels;
GLint skipRows;
GLboolean swapBytes;
};
// Neutral, then each PACK parameter that changes the layout, then all of them at once.
constexpr PackState kPackStates[] = {
{"neutral", 4, 0, 0, 0, GL_FALSE},
{"alignment 1", 1, 0, 0, 0, GL_FALSE},
{"alignment 8", 8, 0, 0, 0, GL_FALSE},
{"row length 53", 4, 53, 0, 0, GL_FALSE},
{"skip pixels 3, skip rows 2", 4, 0, 3, 2, GL_FALSE},
{"everything", 8, 47, 5, 3, GL_FALSE},
};
class PackBufferReadbackScenario : public ScenarioTest {
protected:
void SetUp() override {
ScenarioTest::SetUp();
if (!Ready()) return;
DrainErrors();
glGenFramebuffers(1, &m_fbo);
glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
glDisable(GL_SCISSOR_TEST);
ResetPack();
}
void TearDown() override {
if (!Ready()) return;
ResetPack();
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
for (GLuint buffer : m_buffers) glDeleteBuffers(1, &buffer);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
if (m_fbo != 0) glDeleteFramebuffers(1, &m_fbo);
for (GLuint texture : m_textures) glDeleteTextures(1, &texture);
m_buffers.clear();
m_textures.clear();
m_fbo = 0;
DrainErrors();
ScenarioTest::TearDown();
}
static void ResetPack() {
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glPixelStorei(GL_PACK_ROW_LENGTH, 0);
glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
glPixelStorei(GL_PACK_SKIP_ROWS, 0);
glPixelStorei(GL_PACK_IMAGE_HEIGHT, 0);
glPixelStorei(GL_PACK_SKIP_IMAGES, 0);
glPixelStorei(GL_PACK_SWAP_BYTES, GL_FALSE);
glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
}
static void ApplyPack(const PackState& pack) {
glPixelStorei(GL_PACK_ALIGNMENT, pack.alignment);
glPixelStorei(GL_PACK_ROW_LENGTH, pack.rowLength);
glPixelStorei(GL_PACK_SKIP_PIXELS, pack.skipPixels);
glPixelStorei(GL_PACK_SKIP_ROWS, pack.skipRows);
glPixelStorei(GL_PACK_SWAP_BYTES, pack.swapBytes);
}
static void DrainErrors() {
for (int i = 0; i < 16 && glGetError() != GL_NO_ERROR; ++i) {
}
}
// The bytes a pack state makes a width x height read occupy, from the first byte the
// read may touch (GL 4.6 §8.4.4.1 / §18.2): the skips, then the padded rows, the last
// row tight.
static std::size_t PackedExtent(const PackState& pack, int width, int height, std::size_t bpp) {
const std::size_t rowPixels = pack.rowLength > 0 ? static_cast<std::size_t>(pack.rowLength)
: static_cast<std::size_t>(width);
const std::size_t align = static_cast<std::size_t>(pack.alignment);
const std::size_t stride = (rowPixels * bpp + align - 1) / align * align;
return static_cast<std::size_t>(pack.skipRows) * stride + static_cast<std::size_t>(pack.skipPixels) * bpp +
static_cast<std::size_t>(height - 1) * stride + static_cast<std::size_t>(width) * bpp;
}
GLuint NewTexture() {
GLuint texture = 0;
glGenTextures(1, &texture);
m_textures.push_back(texture);
return texture;
}
GLuint NewBuffer(GLenum target, std::size_t size, GLubyte fill) {
GLuint buffer = 0;
glGenBuffers(1, &buffer);
m_buffers.push_back(buffer);
glBindBuffer(target, buffer);
const std::vector<GLubyte> initial(size, fill);
glBufferData(target, static_cast<GLsizeiptr>(size), initial.data(), GL_DYNAMIC_READ);
return buffer;
}
// An RGBA8 texture holding the pattern, attached as COLOR_ATTACHMENT0 for reading.
GLuint AttachPatternRgba8(int width, int height) {
std::vector<GLubyte> texels(static_cast<std::size_t>(width) * height * 4);
for (int y = 0; y < height; ++y)
for (int x = 0; x < width; ++x) {
const auto t = PatternRgba8(x, y, 0);
std::memcpy(texels.data() + (static_cast<std::size_t>(y) * width + x) * 4, t.data(), 4);
}
const GLuint texture = NewTexture();
glBindTexture(GL_TEXTURE_2D, texture);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, width, height);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, texels.data());
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
glReadBuffer(GL_COLOR_ATTACHMENT0);
EXPECT_EQ(glCheckFramebufferStatus(GL_FRAMEBUFFER), static_cast<GLenum>(GL_FRAMEBUFFER_COMPLETE));
EXPECT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << "pattern upload";
return texture;
}
// glReadPixels of (x, y, width, height) under `pack` into client memory and into a
// pack buffer at `offset`, both pre-filled with kFill; the buffer's bytes are then
// read back by `readBack` and the two must be identical, byte for byte, padding
// included - and the bytes in front of `offset` must still be kFill.
template <typename ReadBack>
void ExpectPackBufferMatchesClientMemory(const PackState& pack, int x, int y, int width, int height,
GLenum type, std::size_t bpp, ReadBack&& readBack) {
ApplyPack(pack);
const std::size_t extent = PackedExtent(pack, width, height, bpp);
std::vector<GLubyte> host(extent, kFill);
glReadPixels(x, y, width, height, GL_RGBA, type, host.data());
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << pack.name << ": client-memory read";
constexpr std::size_t kOffset = 64;
NewBuffer(GL_PIXEL_PACK_BUFFER, kOffset + extent, kFill);
glReadPixels(x, y, width, height, GL_RGBA, type, reinterpret_cast<void*>(kOffset));
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << pack.name << ": pack-buffer read";
std::vector<GLubyte> actual(kOffset + extent, 0);
readBack(actual);
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << pack.name << ": buffer read-back";
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
ResetPack();
std::size_t lead = 0;
for (std::size_t i = 0; i < kOffset; ++i) lead += actual[i] != kFill ? 1 : 0;
EXPECT_EQ(lead, 0u) << pack.name << ": " << lead << " bytes in front of the read's offset moved";
std::size_t bad = 0, first = 0;
for (std::size_t i = 0; i < extent; ++i) {
if (actual[kOffset + i] != host[i] && bad++ == 0) first = i;
}
EXPECT_EQ(bad, 0u) << pack.name << ": " << bad << " of " << extent
<< " bytes differ from the client-memory read, first at byte " << first
<< " (buffer " << static_cast<int>(actual[kOffset + first]) << ", host "
<< static_cast<int>(host[first]) << ")";
}
GLuint m_fbo = 0;
std::vector<GLuint> m_buffers;
std::vector<GLuint> m_textures;
};
TEST_F(PackBufferReadbackScenario, ReadPixelsIntoAPackBufferMatchesClientMemoryUnderEveryPackState) {
if (!Ready()) return;
AttachPatternRgba8(37, 23);
if (HasFatalFailure()) return;
for (const PackState& pack : kPackStates) {
ExpectPackBufferMatchesClientMemory(pack, 2, 1, 31, 19, GL_UNSIGNED_BYTE, 4, [](std::vector<GLubyte>& out) {
glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(out.size()), out.data());
});
if (HasFatalFailure()) return;
}
}
// The map is the OTHER CPU reader, and the one an application that streams readbacks
// through a PBO actually uses: glMapBufferRange(GL_MAP_READ_BIT) must see the pixels the
// server landed, not the bytes the client shadow held before the read.
TEST_F(PackBufferReadbackScenario, MapBufferRangeAfterAPackBufferReadSeesThePixels) {
if (!Ready()) return;
AttachPatternRgba8(37, 23);
if (HasFatalFailure()) return;
for (const PackState& pack : {kPackStates[0], kPackStates[5]}) {
ExpectPackBufferMatchesClientMemory(pack, 0, 0, 37, 23, GL_UNSIGNED_BYTE, 4, [](std::vector<GLubyte>& out) {
void* mapped = glMapBufferRange(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(out.size()),
GL_MAP_READ_BIT);
ASSERT_NE(mapped, nullptr);
std::memcpy(out.data(), mapped, out.size());
glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
});
if (HasFatalFailure()) return;
}
}
// GL_PACK_SWAP_BYTES reverses every component's bytes; the client carries the group
// width and the server swaps, so a wrong width or a skipped swap is a different float.
TEST_F(PackBufferReadbackScenario, SwapBytesIntoAPackBufferMatchesClientMemory) {
if (!Ready()) return;
constexpr int kWidth = 13, kHeight = 9;
std::vector<GLfloat> texels(static_cast<std::size_t>(kWidth) * kHeight * 4);
for (int y = 0; y < kHeight; ++y)
for (int x = 0; x < kWidth; ++x) {
const auto t = PatternRgba32f(x, y);
std::memcpy(texels.data() + (static_cast<std::size_t>(y) * kWidth + x) * 4, t.data(), sizeof(t));
}
const GLuint texture = NewTexture();
glBindTexture(GL_TEXTURE_2D, texture);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA32F, kWidth, kHeight);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, kWidth, kHeight, GL_RGBA, GL_FLOAT, texels.data());
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
glReadBuffer(GL_COLOR_ATTACHMENT0);
ASSERT_EQ(glCheckFramebufferStatus(GL_FRAMEBUFFER), static_cast<GLenum>(GL_FRAMEBUFFER_COMPLETE));
const PackState swapped{"swap bytes, row length 17", 4, 17, 1, 1, GL_TRUE};
ExpectPackBufferMatchesClientMemory(swapped, 0, 0, kWidth, kHeight, GL_FLOAT, 16, [](std::vector<GLubyte>& out) {
glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(out.size()), out.data());
});
}
// glGetTexImage into a pack buffer, 2D and layered: the layered case is the one whose
// layout has an image stride (GL_PACK_IMAGE_HEIGHT) and a skip in the third dimension.
TEST_F(PackBufferReadbackScenario, GetTexImageIntoAPackBufferMatchesClientMemory) {
if (!Ready()) return;
constexpr int kWidth = 11, kHeight = 7, kLayers = 3;
std::vector<GLubyte> texels(static_cast<std::size_t>(kWidth) * kHeight * kLayers * 4);
for (int layer = 0; layer < kLayers; ++layer)
for (int y = 0; y < kHeight; ++y)
for (int x = 0; x < kWidth; ++x) {
const auto t = PatternRgba8(x, y, layer);
std::memcpy(texels.data() + ((static_cast<std::size_t>(layer) * kHeight + y) * kWidth + x) * 4,
t.data(), 4);
}
const GLuint flat = NewTexture();
glBindTexture(GL_TEXTURE_2D, flat);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, kWidth, kHeight);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, texels.data());
const GLuint layered = NewTexture();
glBindTexture(GL_TEXTURE_2D_ARRAY, layered);
glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGBA8, kWidth, kHeight, kLayers);
glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, kWidth, kHeight, kLayers, GL_RGBA, GL_UNSIGNED_BYTE,
texels.data());
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << "texture upload";
struct Shape {
const char* name;
GLenum target;
GLuint texture;
int depth;
GLint rowLength, alignment, imageHeight, skipImages;
};
const Shape shapes[] = {
{"2D, row length 13, alignment 8", GL_TEXTURE_2D, flat, 1, 13, 8, 0, 0},
{"2D array, image height 9, skip images 1", GL_TEXTURE_2D_ARRAY, layered, kLayers, 0, 4, 9, 1},
};
for (const Shape& shape : shapes) {
glBindTexture(shape.target, shape.texture);
glPixelStorei(GL_PACK_ROW_LENGTH, shape.rowLength);
glPixelStorei(GL_PACK_ALIGNMENT, shape.alignment);
glPixelStorei(GL_PACK_IMAGE_HEIGHT, shape.imageHeight);
glPixelStorei(GL_PACK_SKIP_IMAGES, shape.skipImages);
const std::size_t rowPixels = shape.rowLength > 0 ? static_cast<std::size_t>(shape.rowLength) : kWidth;
const std::size_t stride = (rowPixels * 4 + shape.alignment - 1) / shape.alignment * shape.alignment;
const std::size_t imageRows = shape.imageHeight > 0 ? static_cast<std::size_t>(shape.imageHeight) : kHeight;
const std::size_t imageStride = stride * imageRows;
const std::size_t extent = static_cast<std::size_t>(shape.skipImages) * imageStride +
static_cast<std::size_t>(shape.depth - 1) * imageStride +
static_cast<std::size_t>(kHeight - 1) * stride + kWidth * 4u;
std::vector<GLubyte> host(extent, kFill);
glGetTexImage(shape.target, 0, GL_RGBA, GL_UNSIGNED_BYTE, host.data());
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << shape.name << ": client-memory read";
constexpr std::size_t kOffset = 32;
NewBuffer(GL_PIXEL_PACK_BUFFER, kOffset + extent, kFill);
glGetTexImage(shape.target, 0, GL_RGBA, GL_UNSIGNED_BYTE, reinterpret_cast<void*>(kOffset));
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << shape.name << ": pack-buffer read";
std::vector<GLubyte> actual(kOffset + extent, 0);
glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(actual.size()), actual.data());
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
ResetPack();
std::size_t bad = 0, first = 0;
for (std::size_t i = 0; i < kOffset; ++i) bad += actual[i] != kFill ? 1 : 0;
EXPECT_EQ(bad, 0u) << shape.name << ": bytes in front of the offset moved";
bad = 0;
for (std::size_t i = 0; i < extent; ++i)
if (actual[kOffset + i] != host[i] && bad++ == 0) first = i;
EXPECT_EQ(bad, 0u) << shape.name << ": " << bad << " of " << extent
<< " bytes differ from the client-memory read, first at byte " << first;
}
}
// THE UNPACK HALF. A read into a buffer followed by an upload FROM that buffer is a
// GPU-to-GPU copy an application expects to work; under a transport the upload reads the
// client's shadow of the buffer, which the pack read did not touch, so this is exactly
// the case that goes wrong if the upload path forgets that the buffer was GPU-written.
TEST_F(PackBufferReadbackScenario, APackBufferReadFeedsAnUploadFromTheSameBuffer) {
if (!Ready()) return;
constexpr int kWidth = 29, kHeight = 17;
AttachPatternRgba8(kWidth, kHeight);
if (HasFatalFailure()) return;
const GLuint buffer = NewBuffer(GL_PIXEL_PACK_BUFFER, static_cast<std::size_t>(kWidth) * kHeight * 4, kFill);
glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
const GLuint copy = NewTexture();
glBindTexture(GL_TEXTURE_2D, copy);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, kWidth, kHeight);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, buffer);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR)) << "read into the buffer, then upload from it";
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, copy, 0);
std::vector<GLubyte> actual(static_cast<std::size_t>(kWidth) * kHeight * 4, 0);
glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, actual.data());
std::size_t bad = 0;
std::string first;
for (int y = 0; y < kHeight; ++y)
for (int x = 0; x < kWidth; ++x) {
const auto expected = PatternRgba8(x, y, 0);
if (std::memcmp(actual.data() + (static_cast<std::size_t>(y) * kWidth + x) * 4, expected.data(), 4) != 0 &&
bad++ == 0)
first = "(" + std::to_string(x) + "," + std::to_string(y) + ")";
}
EXPECT_EQ(bad, 0u) << bad << " texels of the uploaded copy differ from the pattern, first at " << first;
}
// ORDER AGAINST LATER WRITES. A glBufferSubData into part of the buffer AFTER the read
// must win over the read's bytes there and leave the rest of the read alone - on the
// server the pixels and the later write are two queued ranges of one store, drained in
// record order.
TEST_F(PackBufferReadbackScenario, ALaterBufferSubDataWinsOverThePackReadWhereTheyOverlap) {
if (!Ready()) return;
constexpr int kWidth = 16, kHeight = 8;
AttachPatternRgba8(kWidth, kHeight);
if (HasFatalFailure()) return;
const std::size_t size = static_cast<std::size_t>(kWidth) * kHeight * 4;
std::vector<GLubyte> host(size, kFill);
glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, host.data());
NewBuffer(GL_PIXEL_PACK_BUFFER, size, kFill);
glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
const std::vector<GLubyte> overwrite(40, 0x5A);
glBufferSubData(GL_PIXEL_PACK_BUFFER, 100, static_cast<GLsizeiptr>(overwrite.size()), overwrite.data());
std::vector<GLubyte> actual(size, 0);
glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(size), actual.data());
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR));
std::memcpy(host.data() + 100, overwrite.data(), overwrite.size());
std::size_t bad = 0, first = 0;
for (std::size_t i = 0; i < size; ++i)
if (actual[i] != host[i] && bad++ == 0) first = i;
EXPECT_EQ(bad, 0u) << bad << " bytes differ, first at " << first;
}
// THE WIRE HALF, and the one case that is about the transport rather than the pixels:
// under a transport a pack-buffer read posts NO reply-slot record and marks the buffer
// GPU-written, once per read. MOBILEGL_IPC_PBO_READBACK_SYNC=1 puts the reply form back,
// and this case must then fail on both counters - that is its red-once, recorded in
// docs/archive/notes/p9/.
TEST_F(PackBufferReadbackScenario, APackBufferReadPostsNoReplyAndMarksTheBuffer) {
if (!Ready()) return;
const std::string split = SplitRuntimeSkipReason();
if (!split.empty()) GTEST_SKIP() << split;
constexpr int kWidth = 24, kHeight = 12;
AttachPatternRgba8(kWidth, kHeight);
if (HasFatalFailure()) return;
NewBuffer(GL_PIXEL_PACK_BUFFER, static_cast<std::size_t>(kWidth) * kHeight * 4, kFill);
// A warm-up read, so every state record the read's fill has to publish once is out
// of the way before the counted window opens.
glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR));
constexpr int kReads = 4;
const SplitRuntimeState before = PeekSplitRuntime();
for (int i = 0; i < kReads; ++i) glReadPixels(0, 0, kWidth, kHeight, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
const SplitRuntimeState after = PeekSplitRuntime();
ASSERT_EQ(FirstGLError(), static_cast<GLenum>(GL_NO_ERROR));
EXPECT_EQ(after.replyPostings - before.replyPostings, 0u)
<< "a read into a pack buffer published a reply-slot record: it took the reply form "
"(MOBILEGL_IPC_PBO_READBACK_SYNC=1 does this on purpose)";
EXPECT_EQ(after.packBufferReadbackMarks - before.packBufferReadbackMarks,
static_cast<unsigned long long>(kReads + 1))
<< "every pack-buffer read marks its buffer GPU-written exactly once";
// And the bytes are still right after all of that.
std::vector<GLubyte> actual(static_cast<std::size_t>(kWidth) * kHeight * 4, 0);
glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, static_cast<GLsizeiptr>(actual.size()), actual.data());
const auto corner = PatternRgba8(kWidth - 1, kHeight - 1, 0);
EXPECT_EQ(std::memcmp(actual.data() + actual.size() - 4, corner.data(), 4), 0);
}
} // namespace
} // namespace MGITest
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