Bézier curves

Bézier curves are defined by a context point, like quadratic curves, two control points that define two tangents, and an ending point.

The first part of the curve is tangential to the imaginary line defined by the context point and the first control point. The second part of the curve is tangential to the imaginary line defined by the second control point and the ending point.

The best way to understand how they work is to check out one of these interactive applications:

• Canvas Bézier Curve Example

• IvanK Lib graphics demos

• Nice video tutorial: Bézier curves under the hood

Typical usage of Bézier curves

Source code:

ctx.moveTo(contextX, contextY);

context.bezierCurveTo(controlX1, controlY1, controlX2, controlY2, endX, endY);

// Optional : set lineWidth and stroke color

context.lineWidth = 5;

context.strokeStyle = "#0000ff";

// Draw!

ctx.stroke();

Examples

Example #1

Try this:

Code source:

context.beginPath();

context.moveTo(100, 20);

context.bezierCurveTo(290, -40, 200, 200, 400, 100);

context.lineWidth = 5;

context.strokeStyle = "#0000ff";

context.stroke();

Example #2: path with bezier curve, quadratic curve and line in the same, closed path

Try this:

Extract from source code:

context.beginPath();

context.moveTo(100, 20);

context.lineTo(200, 160);

context.quadraticCurveTo(230, 200, 250, 120);

context.bezierCurveTo(290, -40, 300, 200, 400, 150);

context.lineTo(500, 90);

// TRY COMMENTING THIS LINE OUT

context.closePath();

context.lineWidth = 5;

context.strokeStyle = "#0000ff";

context.stroke();

In this example we use the closePath() method to draw a line between the last path point and the first path point (line 11), so that the drawing looks like a pair of goggles.

Note how the different parts are linked together and make a "path":