GPUBuffer: mapAsync() method

Limited availability

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

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 mapAsync() method of the GPUBuffer interface maps the specified range of the GPUBuffer. It returns a Promise that resolves when the GPUBuffer's content is ready to be accessed. While the GPUBuffer is mapped it cannot be used in any GPU commands.

Once the buffer is successfully mapped (which can be checked via GPUBuffer.mapState), calls to GPUBuffer.getMappedRange() will return an ArrayBuffer containing the GPUBuffer's current values, to be read and updated by JavaScript as required.

When you have finished working with the GPUBuffer values, call GPUBuffer.unmap() to unmap it, making it accessible to the GPU again.

Syntax

mapAsync(mode)
mapAsync(mode, offset, size)

Parameters

mode

A bitwise flag that specifies whether the GPUBuffer is mapped for reading or writing. Possible values are:

GPUMapMode.READ

The GPUBuffer is mapped for reading. Values can be read, but any changes made to the ArrayBuffer returned by GPUBuffer.getMappedRange() will be discarded once GPUBuffer.unmap() is called.

Read-mode mapping can only be used on GPUBuffers that have a usage of GPUBufferUsage.MAP_READ set on them (i.e., when created with GPUDevice.createBuffer()).

GPUMapMode.WRITE

The GPUBuffer is mapped for writing. Values can be read and updated — any changes made to the ArrayBuffer returned by GPUBuffer.getMappedRange() will be saved to the GPUBuffer once GPUBuffer.unmap() is called.

Write-mode mapping can only be used on GPUBuffers that have a usage of GPUBufferUsage.MAP_WRITE set on them (i.e., when created with GPUDevice.createBuffer()).

offset Optional

A number representing the offset, in bytes, from the start of the buffer to the start of the range to be mapped. If offset is omitted, it defaults to 0.

size Optional

A number representing the size, in bytes, of the range to be mapped. If size is omitted, the range mapped extends to the end of the GPUBuffer.

Return value

A Promise that resolves to Undefined when the GPUBuffer's content is ready to be accessed.

Validation

The following criteria must be met when calling mapAsync(), otherwise an OperationError DOMException is thrown, the promise is rejected, and a GPUValidationError is generated:

offset is a multiple of 8.
The total range to be mapped (size if specified, or GPUBuffer.size - offset if not) is a multiple of 4.
The total range to be mapped is inside the bounds of the GPUBuffer.
If mode is GPUMapMode.READ, the GPUBuffer has a usage of GPUBufferUsage.MAP_READ.
If mode is GPUMapMode.WRITE, the GPUBuffer has a usage of GPUBufferUsage.MAP_WRITE.