How to draw a rounded Rectangle on HTML Canvas?
I needed to do the same thing and created a method to do it.
// Now you can just call
var ctx = document.getElementById("rounded-rect").getContext("2d");
// Draw using default border radius,
// stroke it but no fill (function's default values)
roundRect(ctx, 5, 5, 50, 50);
// To change the color on the rectangle, just manipulate the context
ctx.strokeStyle = "rgb(255, 0, 0)";
ctx.fillStyle = "rgba(255, 255, 0, .5)";
roundRect(ctx, 100, 5, 100, 100, 20, true);
// Manipulate it again
ctx.strokeStyle = "#0f0";
ctx.fillStyle = "#ddd";
// Different radii for each corner, others default to 0
roundRect(ctx, 300, 5, 200, 100, {
tl: 50,
br: 25
}, true);
/**
* Draws a rounded rectangle using the current state of the canvas.
* If you omit the last three params, it will draw a rectangle
* outline with a 5 pixel border radius
* @param {CanvasRenderingContext2D} ctx
* @param {Number} x The top left x coordinate
* @param {Number} y The top left y coordinate
* @param {Number} width The width of the rectangle
* @param {Number} height The height of the rectangle
* @param {Number} [radius = 5] The corner radius; It can also be an object
* to specify different radii for corners
* @param {Number} [radius.tl = 0] Top left
* @param {Number} [radius.tr = 0] Top right
* @param {Number} [radius.br = 0] Bottom right
* @param {Number} [radius.bl = 0] Bottom left
* @param {Boolean} [fill = false] Whether to fill the rectangle.
* @param {Boolean} [stroke = true] Whether to stroke the rectangle.
*/
function roundRect(ctx, x, y, width, height, radius, fill, stroke) {
if (typeof stroke === 'undefined') {
stroke = true;
}
if (typeof radius === 'undefined') {
radius = 5;
}
if (typeof radius === 'number') {
radius = {tl: radius, tr: radius, br: radius, bl: radius};
} else {
var defaultRadius = {tl: 0, tr: 0, br: 0, bl: 0};
for (var side in defaultRadius) {
radius[side] = radius[side] || defaultRadius[side];
}
}
ctx.beginPath();
ctx.moveTo(x + radius.tl, y);
ctx.lineTo(x + width - radius.tr, y);
ctx.quadraticCurveTo(x + width, y, x + width, y + radius.tr);
ctx.lineTo(x + width, y + height - radius.br);
ctx.quadraticCurveTo(x + width, y + height, x + width - radius.br, y + height);
ctx.lineTo(x + radius.bl, y + height);
ctx.quadraticCurveTo(x, y + height, x, y + height - radius.bl);
ctx.lineTo(x, y + radius.tl);
ctx.quadraticCurveTo(x, y, x + radius.tl, y);
ctx.closePath();
if (fill) {
ctx.fill();
}
if (stroke) {
ctx.stroke();
}
}<canvas id="rounded-rect" width="500" height="200">
<!-- Insert fallback content here -->
</canvas>- Different radii per corner provided by Corgalore
- See http://js-bits.blogspot.com/2010/07/canvas-rounded-corner-rectangles.html for further explanation
I started with @jhoff's solution, but rewrote it to use width/height parameters, and using arcTo makes it quite a bit more terse:
CanvasRenderingContext2D.prototype.roundRect = function (x, y, w, h, r) {
if (w < 2 * r) r = w / 2;
if (h < 2 * r) r = h / 2;
this.beginPath();
this.moveTo(x+r, y);
this.arcTo(x+w, y, x+w, y+h, r);
this.arcTo(x+w, y+h, x, y+h, r);
this.arcTo(x, y+h, x, y, r);
this.arcTo(x, y, x+w, y, r);
this.closePath();
return this;
}
Also returning the context so you can chain a little. E.g.:
ctx.roundRect(35, 10, 225, 110, 20).stroke(); //or .fill() for a filled rect
The HTML5 canvas doesn't provide a method to draw a rectangle with rounded corners.
How about using the lineTo() and arc() methods?
You can also use the quadraticCurveTo() method instead of the arc() method.