The setIndexBuffer() method of the GPURenderPassEncoder interface sets the current GPUBuffer that will provide index data for subsequent drawing commands.

buffer

A GPUBuffer representing the buffer containing the index data to use for subsequent drawing commands.

indexFormat

An enumerated value that defines the format of the index data contained in buffer. Possible values are:

• "uint16"
• "uint32"

offset Optional

A number representing the offset, in bytes, into buffer where the index data begins. If omitted, offset defaults to 0.

size Optional

A number representing the size, in bytes, of the index data contained in buffer. If omitted, size defaults to the buffer's GPUBuffer.size - offset.

Note on indexFormat

indexFormat determines both the data type of index values in a buffer and, when used with a pipeline that specifies a strip primitive topology ("line-strip" or "triangle-strip"), also determines the primitive restart value. The primitive restart value is an index value indicating that a new primitive should be started rather than continuing to construct the strip with the prior indexed vertices. The value is 0xFFFF for "uint16", or 0xFFFFFFFF for "uint32".

None (Undefined).

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

• buffer's GPUBuffer.usage contains the GPUBufferUsage.INDEX flag.
• offset + size is less than or equal to the buffer's GPUBuffer.size.
• offset is a multiple of indexFormat's byte size (2 for "uint16", 4 for "uint32").

In the WebGPU Samples Shadow Mapping example, setIndexBuffer() is used in two separate render passes in each animation frame, one to draw the main model and one to draw its shadow. Study the example code listing for the full context.

// ...

const commandEncoder = device.createCommandEncoder();
{
  const shadowPass = commandEncoder.beginRenderPass(shadowPassDescriptor);
  shadowPass.setPipeline(shadowPipeline);
  shadowPass.setBindGroup(0, sceneBindGroupForShadow);
  shadowPass.setBindGroup(1, modelBindGroup);
  shadowPass.setVertexBuffer(0, vertexBuffer);
  shadowPass.setIndexBuffer(indexBuffer, "uint16");
  shadowPass.drawIndexed(indexCount);

  shadowPass.end();
}
{
  const renderPass = commandEncoder.beginRenderPass(renderPassDescriptor);
  renderPass.setPipeline(pipeline);
  renderPass.setBindGroup(0, sceneBindGroupForRender);
  renderPass.setBindGroup(1, modelBindGroup);
  renderPass.setVertexBuffer(0, vertexBuffer);
  renderPass.setIndexBuffer(indexBuffer, "uint16");
  renderPass.drawIndexed(indexCount);

  renderPass.end();
}

// ...

• The WebGPU API