The GPURenderBundle interface of the WebGPU API represents a container for pre-recorded bundles of commands.
The command bundles are encoded using a GPURenderBundleEncoder; once the desired commands have been encoded, they are recorded into a GPURenderBundle object instance using the GPURenderBundleEncoder.finish() method.
These command bundles can then be reused across multiple render passes by passing the GPURenderBundle objects into GPURenderPassEncoder.executeBundles() calls. Reusing pre-recoded commands can significantly improve app performance in situations where JavaScript draw call overhead is a bottleneck. Render bundles are most effective in situations where a batch of objects will be drawn the same way across multiple views or frames, with the only differences being the buffer content being used (such as updated matrix uniforms).
A good example is VR rendering. Recording the rendering as a render bundle and then tweaking the view matrix and replaying it for each eye is a more efficient way to issue draw calls for both renderings of the scene.
In the WebGPU Samples Animometer example, a lot of like operations are done on many different objects simultaneously. A render bundle is encoded using the following function:
function recordRenderPass(
passEncoder: GPURenderBundleEncoder | GPURenderPassEncoder
) {
if (settings.dynamicOffsets) {
passEncoder.setPipeline(dynamicPipeline);
} else {
passEncoder.setPipeline(pipeline);
}
passEncoder.setVertexBuffer(0, vertexBuffer);
passEncoder.setBindGroup(0, timeBindGroup);
const dynamicOffsets = [0];
for (let i = 0; i < numTriangles; ++i) {
if (settings.dynamicOffsets) {
dynamicOffsets[0] = i * alignedUniformBytes;
passEncoder.setBindGroup(1, dynamicBindGroup, dynamicOffsets);
} else {
passEncoder.setBindGroup(1, bindGroups[i]);
}
passEncoder.draw(3, 1, 0, 0);
}
}
Later on, a GPURenderBundleEncoder is created, the function is invoked, and the render bundle is recorded using GPURenderBundleEncoder.finish():
const renderBundleEncoder = device.createRenderBundleEncoder({
colorFormats: [presentationFormat],
});
recordRenderPass(renderBundleEncoder);
const renderBundle = renderBundleEncoder.finish();
GPURenderPassEncoder.executeBundles() is then used to reuse the work across multiple render passes to improve performance. Study the example code listing for the full context.
return function doDraw(timestamp) {
if (startTime === undefined) {
startTime = timestamp;
}
uniformTime[0] = (timestamp - startTime) / 1000;
device.queue.writeBuffer(uniformBuffer, timeOffset, uniformTime.buffer);
renderPassDescriptor.colorAttachments[0].view = context
.getCurrentTexture()
.createView();
const commandEncoder = device.createCommandEncoder();
const passEncoder = commandEncoder.beginRenderPass(renderPassDescriptor);
if (settings.renderBundles) {
passEncoder.executeBundles([renderBundle]);
} else {
recordRenderPass(passEncoder);
}
passEncoder.end();
device.queue.submit([commandEncoder.finish()]);
};