I would like to create an arc distortion of an image with canvas.
My goal is to do the same thing as imagemagick but in javascript with canvas: https://legacy.imagemagick.org/usage/distorts/#circular_distorts
Here is the expected result with the angle parameter that corresponds to the images below: 60°, 120°, 180°, 270°, 360°
I only found two interesting codes that go in the right direction:
This experimental script
which works directly on the pixel array but does not keep the aspect ratio of the original image and the angle given as a parameter does not work well: https://github.com/sergiks/canvas-text-arc
This other script
which makes a rotation on each column of the image with drawimage but does not allow to configure the angle of the arc, it is a 360° rotation by default: http://jsfiddle.net/hto1s6fy/
var cv = document.getElementById('cv');
var ig = document.getElementById('ig');
var ctx = cv.getContext('2d');
// draw the part of img defined by the rect (startX, startY, endX, endY) inside
// the circle of center (cx,cy) between radius (innerRadius -> outerRadius)
// - no check performed -
function drawRectInCircle(img, cx, cy, innerRadius, outerRadius, startX, startY, endX, endY) {
var angle = 0;
var step = 1 * Math.atan2(1, outerRadius);
var limit = 2 * Math.PI;
ctx.save();
ctx.translate(cx, cy);
while (angle < limit) {
ctx.save();
ctx.rotate(angle);
ctx.translate(innerRadius, 0);
ctx.rotate(-Math.PI / 2);
var ratio = angle / limit;
var x = startX + ratio * (endX - startX);
ctx.drawImage(img, x, startY, 1, (endY - startY), 0, 0, 1, (outerRadius - innerRadius));
ctx.restore();
angle += step;
}
ctx.restore();
}
var cx = 300,
cy = 300;
var innerRadius = 0;
var outerRadius = 300;
var startX = 0,
endX = 1361,
startY = 0,
endY = 681;
drawRectInCircle(ig, cx, cy, innerRadius, outerRadius, startX, startY, endX, endY);
Imagemagick source code
Finally, I also looked at the C source code of imagemagick but I don't have the skills to transpose it: https://github.com/imagemagick/imagemagick/blob/main/magickcore/distort.c (to see what concerns arc distortion, use the keyword "ArcDistortion")
Though this is an interesting topic and I also like to re-invent the wheel sometimes, it isn't necessary in this case. Someone else had a go at it yet and released a JavaScript library called lens, which replicates some of ImageMagick's filters. Luckily the 'Arc distortion' is among those.
Lens offers a method called distort()
which accepts an input like a <canvas>
element, applies the transformation requested and outputs raw pixel data, which you can then use to make another <canvas>
.
Here's a quick example:
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
ctx.font = "48px sans";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillStyle = "#0";
ctx.fillText("Around the World", canvas.width / 2, canvas.height / 2);
async function makeArc(image, angle, rotate = 0) {
let result = await lens.distort(
image,
lens.Distortion.ARC, [angle, rotate], {
imageVirtualPixelMethod: angle === 360 ? lens.VirtualPixelMethod.HORIZONTAL_TILE : lens.VirtualPixelMethod.TRANSPARENT
}
);
let tempCanv = document.createElement("canvas");
let tempCtx = tempCanv.getContext("2d");
tempCanv.width = result.image.width;
tempCanv.height = result.image.height;
tempCtx.putImageData(result.image.imageData, 0, 0);
document.body.appendChild(tempCanv);
}
makeArc(canvas, 120, 0);
<script src="https://cdn.jsdelivr.net/npm/@alxcube/lens@1.0.0/dist/lens.min.js"></script>
<canvas id="canvas" width="450" height="50"></canvas>