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

source

The GPUBuffer to copy from.

sourceOffset

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

destination

The GPUBuffer to copy to.

destinationOffset

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

size

The number of bytes to copy.

None (Undefined).

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).

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

// ...

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

const output = 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(
  output,
  0, // Source offset
  stagingBuffer,
  0, // Destination offset
  BUFFER_SIZE,
);

// ...

• The WebGPU API