GPUCommandEncoder: copyBufferToBuffer() method

The copyBufferToBuffer() method of the GPUCommandEncoder interface encodes a command that copies data from one GPUBuffer to another.

Syntax

copyBufferToBuffer(source, destination)
copyBufferToBuffer(source, destination, size)
copyBufferToBuffer(source, sourceOffset, destination, destinationOffset, size)

Parameters

source

The GPUBuffer to copy from.

sourceOffset Optional

The offset, in bytes, into the source to begin copying from.

destination

The GPUBuffer to copy to.

destinationOffset Optional

The offset, in bytes, into the destination to begin copying to.

size Optional

The number of bytes to copy.

Return value

None (Undefined).

Validation

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

• The source's GPUBuffer.usage includes the GPUBufferUsage.COPY_SRC flag.
• The destination's GPUBuffer.usage includes the GPUBufferUsage.COPY_DST flag.
• size, sourceOffset, and destinationOffset are all multiples of 4.
• The source's GPUBuffer.size is greater than or equal to sourceOffset + size.
• The destination's GPUBuffer.size is greater than or equal to destinationOffset + size.
• source and destination are different GPUBuffers (you can't copy from and to the same buffer).

Examples

In our basic compute demo, we use copyBufferToBuffer() to copy the contents of our outputBuffer to the stagingBuffer.

// …

// Create an output buffer to read GPU calculations to, and a staging buffer to be mapped for JavaScript access

const outputBuffer = device.createBuffer({
  size: BUFFER_SIZE,
  usage: GPUBufferUsage.STORAGE | GPUBufferUsage.COPY_SRC,
});

const stagingBuffer = device.createBuffer({
  size: BUFFER_SIZE,
  usage: GPUBufferUsage.MAP_READ | GPUBufferUsage.COPY_DST,
});

// …

// Create GPUCommandEncoder to encode commands to issue to the GPU
const commandEncoder = device.createCommandEncoder();

// …

// Copy output buffer to staging buffer
commandEncoder.copyBufferToBuffer(
  outputBuffer,
  0, // Source offset
  stagingBuffer,
  0, // Destination offset
  BUFFER_SIZE,
);

// Since we are copying the entire buffer, this can be shortened to
// commandEncoder.copyBufferToBuffer(outputBuffer, stagingBuffer);

// …

Specifications

Browser compatibility

See also

• The WebGPU API