cal.pub0.org/lib/cropImage.ts

58 lines
1.9 KiB
TypeScript

const MAX_IMAGE_SIZE = 512;
export type Area = {
width: number;
height: number;
x: number;
y: number;
};
const createImage = (url: string) =>
new Promise<HTMLImageElement>((resolve, reject) => {
const image = new Image();
image.addEventListener("load", () => resolve(image));
image.addEventListener("error", (error) => reject(error));
image.setAttribute("crossOrigin", "anonymous"); // needed to avoid cross-origin issues on CodeSandbox
image.src = url;
});
export async function getCroppedImg(imageSrc: string, pixelCrop: Area): Promise<string> {
const image = await createImage(imageSrc);
const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
if (!ctx) throw new Error("Context is null, this should never happen.");
const maxSize = Math.max(image.naturalWidth, image.naturalHeight);
const resizeRatio = MAX_IMAGE_SIZE / maxSize < 1 ? Math.max(MAX_IMAGE_SIZE / maxSize, 0.75) : 1;
// huh, what? - Having this turned off actually improves image quality as otherwise anti-aliasing is applied
// this reduces the quality of the image overall because it anti-aliases the existing, copied image; blur results
ctx.imageSmoothingEnabled = false;
// pixelCrop is always 1:1 - width = height
canvas.width = canvas.height = Math.min(maxSize * resizeRatio, pixelCrop.width);
ctx.drawImage(
image,
pixelCrop.x,
pixelCrop.y,
pixelCrop.width,
pixelCrop.height,
0,
0,
canvas.width,
canvas.height
);
// on very low ratios, the quality of the resize becomes awful. For this reason the resizeRatio is limited to 0.75
if (resizeRatio <= 0.75) {
// With a smaller image, thus improved ratio. Keep doing this until the resizeRatio > 0.75.
return getCroppedImg(canvas.toDataURL("image/jpeg"), {
width: canvas.width,
height: canvas.height,
x: 0,
y: 0,
});
}
return canvas.toDataURL("image/jpeg");
}