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javascript - Render 1 pixel from a 3D array in a HTML5 Canvas using putImageData() and an UInt8ClampedArray

问题描述

I tried my best to render just 1 pixel form a 3D Array in a HTML5 Canvas unsuccessfully.

(I know this has been done before but not with a 3D Array). But converting a 3D array to an Uint8ClampedArray and pushing to an Uint8ClampedArray isn't easy.

HTML5 also doesn't have another way to display a pixel manipulatable image.

Is it correct that putImageData() is for rendering vertical strings of pixels?

Here is my code, the problem is marked with: "WHAT DO I GOTTA DO HERE":

<!DOCTYPE html>
<html lang="en" + dir="ltr">
  <head>
    <meta charset="UTF-8">
    <title>
      Index.html
    </title>
  </head>
  <body style="margin: 0px; padding: 0px;">
    <canvas id="canvas">
    </canvas>
    <script>
      let a = new Array();
      a.push([]);
      a[x.length - 1].push([]);
      a[x.length - 1][a[a.length - 1].length - 1].push(0);
      a[x.length - 1][a[a.length - 1].length - 1].push(0);
      a[x.length - 1][a[a.length - 1].length - 1].push(0);
      a[x.length - 1][a[a.length - 1].length - 1].push(255);
      document.getElementById("canvas").getContext("2d").putImageData(new 
      ImageData(new Uint8ClampedArray("WHAT DO I GOTTA DO HERE"), 1, 1), 1, 
      1);
    </script>
  </body>    
</html>

To test it you can use:

console.log(a);
console.log(a[0]);
console.log(a[0][0]);
console.log(a[0][0][0]);

标签： javascripthtml5-canvasarray-pushputimagedatauint8array

解决方案

在画布上绘制 200 x 200 的红色块。需要<canvas></canvas>

我建议不要使用 3D 数组，因为它看起来不必要地复杂

const width = 200;
const height = 200;

const canvas = document.getElementsByTagName('canvas')[0];
const context = canvas.getContext('2d');
canvas.width = width;
canvas.height = height;
const destData = new ImageData(width, height);
const dData = destData.data;

for (let y = 0; y < height; y++) {
  for (let x = 0; x < width; x++) {
    const o = 4 * (y * width + x);
    dData[o] = 255; // R
    dData[o + 1] = 0; // G
    dData[o + 2] = 0; // B
    dData[o + 3] = 255; // A
  }
}

context.putImageData(destData, 0, 0);

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