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row_padding.ts
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row_padding.ts
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
/** Return value for {@linkcode getRowPadding}. */
export interface Padding {
/** The number of bytes per row without padding calculated. */
unpadded: number;
/** The number of bytes per row with padding calculated. */
padded: number;
}
/** Buffer-Texture copies must have [`bytes_per_row`] aligned to this number. */
export const COPY_BYTES_PER_ROW_ALIGNMENT = 256;
/** Number of bytes per pixel. */
export const BYTES_PER_PIXEL = 4;
/**
* Calculates the number of bytes including necessary padding when passing a {@linkcode GPUImageCopyBuffer}.
*
* Ref: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
*
* @example
* ```ts
* import { getRowPadding } from "https://deno.land/std@$STD_VERSION/webgpu/row_padding.ts";
*
* getRowPadding(2); // { unpadded: 8, padded: 256 }
* ```
*/
export function getRowPadding(width: number): Padding {
// It is a WebGPU requirement that
// GPUImageCopyBuffer.layout.bytesPerRow % COPY_BYTES_PER_ROW_ALIGNMENT == 0
// So we calculate paddedBytesPerRow by rounding unpaddedBytesPerRow
// up to the next multiple of COPY_BYTES_PER_ROW_ALIGNMENT.
const unpaddedBytesPerRow = width * BYTES_PER_PIXEL;
const paddedBytesPerRowPadding = (COPY_BYTES_PER_ROW_ALIGNMENT -
(unpaddedBytesPerRow % COPY_BYTES_PER_ROW_ALIGNMENT)) %
COPY_BYTES_PER_ROW_ALIGNMENT;
const paddedBytesPerRow = unpaddedBytesPerRow + paddedBytesPerRowPadding;
return {
unpadded: unpaddedBytesPerRow,
padded: paddedBytesPerRow,
};
}
/**
* Creates a new buffer while removing any unnecessary empty bytes.
* Useful for when wanting to save an image as a specific format.
*
* @example
* ```ts
* import { resliceBufferWithPadding } from "https://deno.land/std@$STD_VERSION/webgpu/row_padding.ts";
*
* const input = new Uint8Array([0, 255, 0, 255, 120, 120, 120]);
* resliceBufferWithPadding(input, 1, 1); // Uint8Array(4) [ 0, 255, 0, 255 ]
* ```
*/
export function resliceBufferWithPadding(
buffer: Uint8Array,
width: number,
height: number,
): Uint8Array {
const { padded, unpadded } = getRowPadding(width);
const outputBuffer = new Uint8Array(unpadded * height);
for (let i = 0; i < height; i++) {
const slice = buffer
.slice(i * padded, (i + 1) * padded)
.slice(0, unpadded);
outputBuffer.set(slice, i * unpadded);
}
return outputBuffer;
}