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// GPU texture readback utility implementation
// Extracts texture pixels to CPU memory for offline processing
#include "gpu/texture_readback.h"
#if !defined(STRIP_ALL)
#include <cassert>
#include <cstdio>
#include <cstring>
// Callback state for async buffer mapping
struct MapState {
bool done = false;
WGPUMapAsyncStatus status = WGPUMapAsyncStatus_Unknown;
};
std::vector<uint8_t> read_texture_pixels(
WGPUInstance instance,
WGPUDevice device,
WGPUTexture texture,
int width,
int height) {
// Align bytes per row to 256 (COPY_BYTES_PER_ROW_ALIGNMENT)
const uint32_t bytes_per_pixel = 4; // BGRA8
const uint32_t unaligned_bytes_per_row = width * bytes_per_pixel;
const uint32_t aligned_bytes_per_row =
((unaligned_bytes_per_row + 255) / 256) * 256;
const size_t buffer_size = aligned_bytes_per_row * height;
std::vector<uint8_t> pixels(width * height * bytes_per_pixel);
// Create staging buffer for readback (with aligned size)
const WGPUBufferDescriptor buffer_desc = {
.usage = WGPUBufferUsage_CopyDst | WGPUBufferUsage_MapRead,
.size = buffer_size,
};
WGPUBuffer staging = wgpuDeviceCreateBuffer(device, &buffer_desc);
assert(staging && "Failed to create staging buffer");
// Create command encoder for copy operation
const WGPUCommandEncoderDescriptor enc_desc = {};
WGPUCommandEncoder encoder =
wgpuDeviceCreateCommandEncoder(device, &enc_desc);
// Copy texture to buffer
const WGPUTexelCopyTextureInfo src = {
.texture = texture,
.mipLevel = 0,
.origin = {0, 0, 0},
};
const WGPUTexelCopyBufferInfo dst = {
.buffer = staging,
.layout =
{
.bytesPerRow = aligned_bytes_per_row,
.rowsPerImage = static_cast<uint32_t>(height),
},
};
const WGPUExtent3D copy_size = {static_cast<uint32_t>(width),
static_cast<uint32_t>(height), 1};
wgpuCommandEncoderCopyTextureToBuffer(encoder, &src, &dst, ©_size);
// Submit commands
WGPUCommandBuffer commands = wgpuCommandEncoderFinish(encoder, nullptr);
WGPUQueue queue = wgpuDeviceGetQueue(device);
wgpuQueueSubmit(queue, 1, &commands);
wgpuCommandBufferRelease(commands);
wgpuCommandEncoderRelease(encoder);
// Wait for copy to complete before mapping
wgpuDevicePoll(device, true, nullptr);
// Map buffer for reading (API differs between Win32 and native)
#if defined(DEMO_CROSS_COMPILE_WIN32)
// Win32: Old callback API
MapState map_state = {};
auto map_cb = [](WGPUBufferMapAsyncStatus status, void* userdata) {
MapState* state = static_cast<MapState*>(userdata);
state->status = status;
state->done = true;
};
wgpuBufferMapAsync(staging, WGPUMapMode_Read, 0, buffer_size, map_cb,
&map_state);
#else
// Native: New callback info API
MapState map_state = {};
auto map_cb = [](WGPUMapAsyncStatus status, WGPUStringView message,
void* userdata, void* user2) {
(void)message;
(void)user2;
MapState* state = static_cast<MapState*>(userdata);
state->status = status;
state->done = true;
};
WGPUBufferMapCallbackInfo map_info = {};
map_info.mode = WGPUCallbackMode_AllowProcessEvents; // Fire during ProcessEvents
map_info.callback = map_cb;
map_info.userdata1 = &map_state;
wgpuBufferMapAsync(staging, WGPUMapMode_Read, 0, buffer_size, map_info);
#endif
// Wait for mapping to complete (synchronous blocking)
for (int i = 0; i < 100 && !map_state.done; ++i) {
#if defined(__EMSCRIPTEN__)
emscripten_sleep(10);
#else
wgpuDevicePoll(device, true, nullptr);
#endif
}
if (!map_state.done || map_state.status != WGPUMapAsyncStatus_Success) {
wgpuBufferRelease(staging);
return pixels; // Return empty on timeout or failure
}
// Copy data from mapped buffer (handle row padding)
const uint8_t* mapped_data = static_cast<const uint8_t*>(
wgpuBufferGetConstMappedRange(staging, 0, buffer_size));
if (mapped_data) {
// If rows are aligned, copy row by row to remove padding
if (aligned_bytes_per_row != unaligned_bytes_per_row) {
for (int y = 0; y < height; ++y) {
memcpy(pixels.data() + y * unaligned_bytes_per_row,
mapped_data + y * aligned_bytes_per_row,
unaligned_bytes_per_row);
}
} else {
// No padding, direct copy
memcpy(pixels.data(), mapped_data, pixels.size());
}
}
// Cleanup
wgpuBufferUnmap(staging);
wgpuBufferRelease(staging);
return pixels;
}
#endif // !defined(STRIP_ALL)
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