lc-runtime

name	lc_runtime
description	Runtime API: Context, Device, Stream, buffers, images, ray tracing, and rasterization.

LuisaCompute Runtime API

Covers luisa/runtime/ classes for GPU compute: context/device management, memory, execution, ray tracing, rasterization, presentation.

Context

#include <luisa/runtime/context.h>
luisa::compute::Context ctx{argv[0]};
// or: Context ctx{argv[0], data_dir};

for (auto &&backend : ctx.installed_backends()) {
    auto names = ctx.backend_device_names(backend);
}
Device device = ctx.create_default_device();

Device

#include <luisa/runtime/device.h>
Device device = ctx.create_device("cuda");  // or "dx", "cpu", "metal"

DeviceConfig cfg{.device_index = 0, .inqueue_buffer_limit = false};
Device device = ctx.create_device("cuda", &cfg, true/*validation*/);

auto backend = device.backend_name();
auto warp = device.compute_warp_size();

Resource Creation

Buffer<float> buf = device.create_buffer<float>(1024);
Buffer<MyStruct> sbuf = device.create_buffer<MyStruct>(100);
Image<float> img = device.create_image<float>(PixelStorage::FLOAT4, w, h);
Image<float> mip = device.create_image<float>(PixelStorage::FLOAT4, w, h, mips);
Volume<float> vol = device.create_volume<float>(PixelStorage::FLOAT4, w, h, d);
ByteBuffer bb = device.create_byte_buffer(size_bytes);
BindlessArray heap = device.create_bindless_array(65536);
IndirectDispatchBuffer indirect = device.create_indirect_dispatch_buffer(capacity);

Stream

#include <luisa/runtime/stream.h>
Stream stream = device.create_stream();
Stream compute = device.create_stream(StreamTag::COMPUTE);
Stream graphics = device.create_stream(StreamTag::GRAPHICS);
stream.set_name("my stream");

Events

#include <luisa/runtime/event.h>
Event event = device.create_event();
TimelineEvent timeline = device.create_timeline_event();

stream << event.signal();
stream << event.wait();
stream << graphics_event.wait(frame_index);
stream << graphics_event.signal(frame_index);
timeline.synchronize(frame_index);

Buffer

#include <luisa/runtime/buffer.h>
Buffer<float> buf = device.create_buffer<float>(1024);

// Transfer
stream << buf.copy_from(host_data);
stream << buf.copy_to(host_data);

// Views
auto view = buf.view(offset, count);
auto elem_view = buf.view().as<float>();  // for atomic operations
buf.set_name("vertex data");

Buffer-to-Buffer Copy

Use BufferView::copy_from(BufferView<T>) or BufferView::copy_to(BufferView<T>) — these work in both normal and SAFE builds.

Buffer<float> src = device.create_buffer<float>(1024);
Buffer<float> dst = device.create_buffer<float>(1024);
Buffer<float> readback = device.create_buffer<float>(1024);

// ✅ Correct (SAFE-mode compatible): go through .view()
stream << dst.view().copy_from(src);            // BufferView::copy_from(BufferView)
stream << readback.view().copy_from(src);       // BufferView::copy_from(BufferView)

// ❌ Wrong (fails in SAFE mode): Buffer::copy_from(BufferView<T>)
// is guarded by #ifndef LUISA_ENABLE_SAFE_MODE
// stream << dst.copy_from(src.view());          // compile error in SAFE

SAFE Build Mode (LUISA_ENABLE_SAFE_MODE)

Define LUISA_ENABLE_SAFE_MODE at build time to disable unsafe raw-pointer overloads, enabling runtime validation of buffer creation. This is controlled by the cmake option ENABLE_SAFE_MODE in the project.

What is excluded in SAFE mode (#ifndef LUISA_ENABLE_SAFE_MODE blocks in include/luisa/runtime/buffer.h):

Class	Excluded overloads
Buffer<T>	copy_to(void*)
copy_to(BufferView<T>)
copy_to(const ByteBufferView&)
copy_from(const void*)
copy_from(const void*, move_only_function)
copy_from(BufferView<T>)
copy_from(const ByteBufferView&)
BufferView<T>	copy_to(void*)
copy_from(const void*)

What remains available (works in both modes):

API	Example
Buffer::copy_to(luisa::span<U>) / Buffer::copy_from(luisa::span<U>)	buf.copy_from(luisa::span{host_vec})
BufferView::copy_to(luisa::span<U>) / BufferView::copy_from(luisa::span<U>)	buf.view().copy_to(luisa::span{host_vec})
BufferView::copy_to(BufferView<T>) / BufferView::copy_from(BufferView<T>)	dst.view().copy_from(src)
BufferView::copy_to(const ByteBufferView&) / BufferView::copy_from(const ByteBufferView&)	buf.view().copy_to(byte_view)

To pass the build in SAFE mode: Always go through BufferView or luisa::span overloads instead of the Buffer<T> convenience overloads that are guarded. For buffer-to-buffer copy, change dst.copy_from(src.view()) → dst.view().copy_from(src). For raw-pointer transfers, change buf.copy_from(data_ptr) → buf.copy_from(luisa::span{ptr, count}).

Image & Volume

#include <luisa/runtime/image.h>
Image<float> img = device.create_image<float>(PixelStorage::FLOAT4, w, h);
Image<float> img2 = device.create_image<float>(swapchain.backend_storage(), size);
// Mipmapped: device.create_image<float>(PixelStorage::FLOAT4, w, h, mips);
// Simultaneous access: device.create_image<float>(PixelStorage::FLOAT4, w, h, 1, true);

#include <luisa/runtime/volume.h>
Volume<float> vol = device.create_volume<float>(PixelStorage::FLOAT4, w, h, d);

Sparse Images and Volumes

Sparse image/volume mip counts follow the same convention as regular textures: zero requests the full chain and larger requests are clamped to the logical maximum. Tile map and unmap regions are validated against the selected mip's ceil-divided tile grid, not the base extent or a floor-divided grid. Counts must be nonzero and range arithmetic must not wrap. Sparse copy regions use the same validation, convert tiles to texel offsets, and clip the final partial tile to the selected mip extent; buffer-backed copies must provide enough bytes for that clipped texel region.

Sparse buffers use the same nonzero-count and checked-range rules over a ceil-divided byte tile grid. Every sparse map operation requires a valid heap created by the same DeviceInterface as the sparse resource.

Image in Kernels

Kernel2D k = [&](ImageFloat img) {
    UInt2 coord = dispatch_id().xy();
    Float4 c = img.read(coord);
    img.write(coord, make_float4(1,0,0,1));
};

BindlessArray

#include <luisa/runtime/bindless_array.h>
BindlessArray heap = device.create_bindless_array(64);
heap.emplace_on_update(slot, buffer);
heap.emplace_on_update(slot, image, TextureSampler::linear_linear_mirror());
stream << heap.update() << synchronize();

// Kernel:
Kernel1D k = [&](Var<BindlessArray> heap) {
    auto v = heap.buffer<float>(slot).read(idx);
    auto c = heap.texture2d(slot).sample(uv);
};

Swapchain

#include <luisa/runtime/swapchain.h>
Swapchain swapchain = device.create_swapchain(stream, SwapchainOption{
    .display = window.native_display(),
    .window = window.native_handle(),
    .size = resolution,
    .wants_hdr = false,
    .wants_vsync = true,
    .back_buffer_count = 3});
stream << swapchain.present(image);

Ray Tracing

#include <luisa/runtime/rtx/accel.h>
#include <luisa/runtime/rtx/mesh.h>
#include <luisa/runtime/rtx/curve.h>

Mesh mesh = device.create_mesh(vertex_buffer, triangle_buffer);
Accel accel = device.create_accel();
accel.emplace_back(mesh, transform);
accel.emplace_back(mesh, transform, visibility_mask);
stream << mesh.build() << accel.build();
stream << accel.update_instance_buffer();

Curve curve = device.create_curve(CurveBasis::CUBIC_BSPLINE, cp_buf, seg_buf);

Ray Tracing Kernel

Kernel2D trace = [&](AccelVar accel, BufferFloat4 img) {
    Var<Ray> ray = make_ray(origin, direction);
    Var<TriangleHit> hit = accel.intersect(ray, {});
    $if (!hit->miss()) {
        Float3 c = triangle_interpolate(hit.bary, v0, v1, v2);
    };
};

Rasterization

#include <luisa/runtime/raster/depth_buffer.h>
#include <luisa/runtime/raster/raster_scene.h>
#include <luisa/runtime/raster/raster_shader.h>

DepthBuffer depth = device.create_depth_buffer(DepthFormat::D32, size);
auto raster_shader = device.compile(raster_kernel, mesh_format);
RasterScene scene = device.create_raster_scene(vertex_buffer, index_buffer);

CommandList

Batch commands for efficient submission:

CommandList cmdlist = CommandList::create();
cmdlist << kernel.dispatch(w, h) << buffer.copy_to(host_data);
stream << cmdlist.commit() << synchronize();

Prefer merging dispatch + transfers into one CommandList + single commit/synchronize over separate stream submissions.

Complete Example

#include <luisa/luisa-compute.h>
using namespace luisa::compute;

int main(int argc, char *argv[]) {
    Context ctx{argv[0]};
    Device device = ctx.create_device("cuda");
    Stream stream = device.create_stream();
    Buffer<float> buf = device.create_buffer<float>(1024);

    Kernel1D k = [&](BufferVar<float> buf) {
        auto idx = dispatch_id().x;
        buf.write(idx, buf.read(idx) + 1.0f);
    };

    auto shader = device.compile(k);
    stream << shader(buf).dispatch(1024) << synchronize();
}

Common Patterns

Multi-Stream Sync

Stream compute = device.create_stream(StreamTag::COMPUTE);
Stream graphics = device.create_stream(StreamTag::GRAPHICS);
Event event = device.create_event();
compute << shader().dispatch(w, h) << event.signal();
graphics << event.wait() << swapchain.present(img);

Triple Buffering

TimelineEvent timeline = device.create_timeline_event();
uint64_t frame = 0;
while (running) {
    if (frame >= 3) timeline.synchronize(frame - 2);
    stream << shader().dispatch(w, h) << timeline.signal(++frame);
}

Buffer Upload/Download

Always prefer luisa::span<T> overloads for SAFE-mode compatibility:

luisa::vector<float> host_data(1024, 1.0f);

// ✅ span-based (SAFE-mode compatible)
stream << buf.copy_from(luisa::span{host_data}) << synchronize();
stream << buf.copy_to(luisa::span{host_data}) << synchronize();

// ❌ raw-pointer (fails in SAFE mode)
// stream << buf.copy_to(host_data.data()) << synchronize();
// stream << buf.copy_from(host_data.data()) << synchronize();

Key Headers

Header	Class
luisa/runtime/context.h	Context
luisa/runtime/device.h	Device
luisa/runtime/stream.h	Stream
luisa/runtime/event.h	Event, TimelineEvent
luisa/runtime/buffer.h	Buffer
luisa/runtime/image.h	Image
luisa/runtime/volume.h	Volume
luisa/runtime/swapchain.h	Swapchain
luisa/runtime/bindless_array.h	BindlessArray
luisa/runtime/dispatch_buffer.h	IndirectDispatchBuffer
luisa/runtime/command_list.h	CommandList
luisa/runtime/rtx/accel.h	Accel
luisa/runtime/rtx/mesh.h	Mesh
luisa/runtime/rtx/curve.h	Curve
luisa/runtime/rtx/ray.h	Ray, hit types
luisa/runtime/raster/raster_shader.h	RasterShader
luisa/runtime/raster/raster_scene.h	RasterScene