GPUBuffer: mapAsync() method

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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 mapState), calls to 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 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 getMappedRange() will be discarded once 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 createBuffer()).

    • GPUMapMode.WRITE

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

Examples

See the main GPUBuffer page for an example.

Specifications

Browser compatibility

See also

• The WebGPU API