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/**
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Converts an image mask represented as a binary image (foreground pixels are
* `>1` and background pixels are `0`) stored in a Uint8Array to an RGBA
* representation where background pixels have an alpha value of 0 and
* foreground pixels have an alpha value of 255. This is useful for compositing
* the mask onto another image.
*
* ```typescript
* const rgba = convertMaskDataToRGBA(mask.data);
* ```
*
* @param data - The image mask represented as a Uint8Array
* @returns A new Uint8ClampedArray representing the mask in RGBA format
*/
export function convertMaskToRGBA(data: Uint8Array): Uint8ClampedArray {
// Shifting pixels instead of assigning them individually per pixel is
// much faster. See JSPerf benchamrk: https://jsperf.app/morifo
const len = data.length;
const tempData = new Uint32Array(len);
const RGA = 0x00ffffff;
const FOREGROUND = 0xff000000;
const BACKGROUND = 0x00000000;
for (let i = 0; i < len; i++) {
const alpha = data[i] > 0 ? FOREGROUND : BACKGROUND; // alpha is the high byte. Bits 24-31
tempData[i] = alpha + RGA;
}
return new Uint8ClampedArray(tempData.buffer);
}
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