react-nice-scroll/src/utils.ts

A React library to smooth scroll and scroll-based animations.

export const preloadImage = (src: string) => {
  return new Promise((resolve, reject) => {
    const img = new Image();
    const xhr = new XMLHttpRequest();

    xhr.open('GET', src, true);
    xhr.responseType = 'blob';
    xhr.onload = () => {
      img.src = URL.createObjectURL(xhr.response);
      img.onload = () => resolve(img);
    };
    xhr.onerror = () => reject();
    xhr.send();
  });
};

export const preloadImages = (urls: string[]) => {
  return Promise.all(urls.map((src) => preloadImage(src)));
};

export const calcDrawImage = (ctx: CanvasRenderingContext2D, image: any, left = 0.5, top = 0.5) => {
  const cWidth = ctx.canvas.width;
  const cHeight = ctx.canvas.height;
  const width = image.width;
  const height = image.height;
  const ratio = width / height;
  const cRatio = cWidth / cHeight;
  let resultHeight, resultWidth;

  if (ratio > cRatio) {
    resultHeight = cHeight;
    resultWidth = cHeight * ratio;
  } else {
    resultWidth = cWidth;
    resultHeight = cWidth / ratio;
  }

  ctx.drawImage(image, (cWidth - resultWidth) * left, (cHeight - resultHeight) * top, resultWidth, resultHeight);
};