scratch-paint/src/helper/bitmap.js

import paper from '@scratch/paper';

const rowBlank_ = function (imageData, width, y) {
    for (let x = 0; x < width; ++x) {
        if (imageData.data[(y * width << 2) + (x << 2) + 3] !== 0) return false;
    }
    return true;
};

const columnBlank_ = function (imageData, width, x, top, bottom) {
    for (let y = top; y < bottom; ++y) {
        if (imageData.data[(y * width << 2) + (x << 2) + 3] !== 0) return false;
    }
    return true;
};

// Adapted from Tim Down's https://gist.github.com/timdown/021d9c8f2aabc7092df564996f5afbbf
// Trims transparent pixels from edges.
const trim = function (raster) {
    const width = raster.width;
    const imageData = raster.getImageData(raster.bounds);
    let top = 0;
    let bottom = imageData.height;
    let left = 0;
    let right = imageData.width;

    while (top < bottom && rowBlank_(imageData, width, top)) ++top;
    while (bottom - 1 > top && rowBlank_(imageData, width, bottom - 1)) --bottom;
    while (left < right && columnBlank_(imageData, width, left, top, bottom)) ++left;
    while (right - 1 > left && columnBlank_(imageData, width, right - 1, top, bottom)) --right;

    return raster.getSubRaster(new paper.Rectangle(left, top, right - left, bottom - top));
};

export {
    trim
};