canvas-opacity-blend-modes-expected.html

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<!DOCTYPE html>

<body>

</body>

<script>

/*

  Compare how the opacity is handled in different blend modes when setting its

  value with filters or with properties.

*/

  function drawSquares(canvasId, x, y, compositeOperation) {

    var canvas = document.getElementById(canvasId);

    var ctx = canvas.getContext('2d');

    canvas.style.position = 'absolute';

    canvas.style.left = `${x}px`;

    canvas.style.top = `${y}px`;

    ctx.globalCompositeOperation = 'source-over';

    ctx.globalAlpha = 1.0;

    ctx.fillStyle = 'green';

    ctx.fillRect(0, 0, 200, 60);

    ctx.fillStyle = 'blue';

    ctx.fillRect(0, 0, 50, 50);

    ctx.globalAlpha = 0.7;

    ctx.fillStyle = 'red';

    ctx.fillRect(50, 0, 50, 50);

    ctx.globalCompositeOperation = compositeOperation;

    ctx.globalAlpha = 0.5;

    ctx.fillStyle = 'yellow';

    ctx.fillRect(25, 25, 50, 50);

  // Fomatted in the same matrix as the drawn elements.

  var compositeOperations =

    ['source-over', 'source-in', 'source-out', 'source-atop','destination-over',

    'destination-in', 'destination-out', 'destination-atop', 'lighter', 'copy',

    'xor', 'multiply', 'screen', 'overlay', 'darken',

    'lighten', 'color-dodge', 'color-burn', 'hard-light', 'soft-light',

    'difference', 'exclusion', 'hue', 'saturation', 'color',

    'luminosity'];

  for (var i = 0; i < compositeOperations.length; i++){

    var canvas = document.createElement('canvas');

    canvas.id = `canvas-${i}`;

    document.body.appendChild(canvas);

    drawSquares(canvas.id, (i%5)*300, Math.floor(i/5)*300,

      compositeOperations[i]);

</script>