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Tip revision: f501e13e0c86d67b6530673548b9a4c24eaf4240 authored by Joshua Bell on 13 March 2018, 18:24:51 UTC
add back in missing words

Tip revision: f501e13

canvas_colorsandstyles_createlineargradient_001.htm

<!doctype HTML>
<html>
    <head>
        <title>HTML5 Canvas Test:  createlinearGradient() with two points same</title>
        <script src="/resources/testharness.js"></script>
        <script src="/resources/testharnessreport.js"></script>
        <link rel="author" title="Microsoft" href="http://www.microsoft.com" />
        <link rel="help" href="http://www.w3.org/TR/2dcontext/#dom-context-2d-createlineargradient" />
        <meta name="assert" content="If the two points in a linear gradient have identical x,y coordinates, the canvas must paint nothing." />
        <script type="text/javascript">
            async_test(function(t) {
              window.addEventListener("load", t.step_func_done(function runTest() {
                var canvas = document.getElementById("canvas1");
                var ctx = canvas.getContext("2d");
                var width = canvas.width;
                var height = canvas.height;

                // Start by drawing a left to right, green-to-blue linear gradient.
                var lingrad = ctx.createLinearGradient(0, 50, 100, 50);
                lingrad.addColorStop(0, "rgba(0, 255, 0, 1.0)");
                lingrad.addColorStop(1, "rgba(0, 0, 255, 1.0)");
                ctx.fillStyle = lingrad;
                ctx.fillRect(0, 0, 100, 50);

                // Get the current state of the canvas
                var initial = ctx.getImageData(0, 0, width, height);

                // Nothing must be drawn if the two points in the linear gradient are the same.
                lingrad = ctx.createLinearGradient(100, 100, 100, 100);
                lingrad.addColorStop(0, "rgba(255, 0, 0, 1.0)");
                lingrad.addColorStop(1, "rgba(255, 0, 0, 1.0)");
                ctx.fillStyle = lingrad;
                ctx.fillRect(0, 0, 300, 150);

                // Check that nothing is drawn.
                var after = ctx.getImageData(0, 0, width, height);

                // Asserts
                assert_equals(initial.width, after.width, "widths are equal");
                assert_equals(initial.height, after.height, "heights are equal");
                assert_array_equals(initial.data, after.data, "data are equal");

                for (var i = 0; i < after.data.length; i += 4) {
                  var r = after.data[i];
                  var g = after.data[i+1];
                  var b = after.data[i+2];
                  var a = after.data[i+3];
                  assert_false(r == 0xFF && g == 0 && b == 0 && a == 0xFF, "no red");
                }
              }));
            }, "linear gradient from point to self draws nothing");
        </script>
    </head>
    <body>
        <p>Description: If the two points in a linear gradient have identical x,y coordinates, the canvas must paint nothing.</p>
        <p>Test passes if there is one left-to-right, green-to-blue linear gradient seen on the page and no red is seen on the page.</p>
        <canvas id="canvas1" width="300" height="150">Browser does not support HTML5 Canvas.</canvas>
    </body>
</html>

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