GPURenderPassEncoder: drawIndirect() method

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Note: This feature is available in Web Workers.

The drawIndirect() method of the GPURenderPassEncoder interface draws primitives using parameters read from a GPUBuffer.

A GPUBuffer containing the vertexCount, instanceCount, firstVertex, and firstInstance values needed to carry out the drawing operation. The buffer must contain a tightly packed block of four 32-bit unsigned integer values representing the values (16 bytes total), given in the same order as the arguments for GPURenderPassEncoder.draw(). So for example:

const uint32 = new Uint32Array(4);
uint32[0] = 3; // The vertexCount value
uint32[1] = 1; // The instanceCount value
uint32[2] = 0; // The firstVertex value
uint32[3] = 0; // The firstInstance value

// Write values into a GPUBuffer
device.queue.writeBuffer(buffer, 0, uint32, 0, uint32.length);

Note: The indirect-first-instance feature needs to be enabled for non-zero firstInstance values to be used. If the indirect-first-instance feature is not enabled and firstInstance is not zero, the drawIndirect() call will be treated as a no-op.

indirectOffset

The offset, in bytes, into indirectBuffer where the value data begins.

Return value

None (Undefined).

Validation

The following criteria must be met when calling drawIndirect(), otherwise a GPUValidationError is generated and the GPURenderPassEncoder becomes invalid:

indirectBuffer's GPUBuffer.usage contains the GPUBufferUsage.INDIRECT flag.
indirectOffset + the total size specified by the value parameters in the indirectBuffer is less than or equal to the indirectBuffer's GPUBuffer.size.
indirectOffset is a multiple of 4.

Examples

// ...

// Create GPURenderPassEncoder
const passEncoder = commandEncoder.beginRenderPass(renderPassDescriptor);

// Set pipeline and vertex buffer
passEncoder.setPipeline(renderPipeline);
passEncoder.setVertexBuffer(0, vertexBuffer);

// Create drawIndirect values
const uint32 = new Uint32Array(4);
uint32[0] = 3;
uint32[1] = 1;
uint32[2] = 0;
uint32[3] = 0;

// Create a GPUBuffer and write the draw values into it
const drawValues = device.createBuffer({
  size: 16,
  usage: GPUBufferUsage.COPY_DST | GPUBufferUsage.INDIRECT,
});
device.queue.writeBuffer(drawValues, 0, uint32, 0, uint32.length);

// Draw the vertices
passEncoder.drawIndirect(drawValues, 0);

// End the render pass
passEncoder.end();

// End frame by passing array of GPUCommandBuffers to command queue for execution
device.queue.submit([commandEncoder.finish()]);

// ...

Specifications

Specification
WebGPU # dom-gpurendercommandsmixin-drawindirect

Browser compatibility

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