How can I draw smooth curves through multiple points in HTML5 Canvas?

Drawing Smooth Curves Through Multiple Points in HTML5 Canvas

When creating drawing applications, capturing mouse movements and connecting them using line segments often results in jagged lines. To achieve smooth curves, it's necessary to explore alternative techniques.

Existing Drawing Functions

HTML5 Canvas provides three drawing functions for connecting points:

• lineTo: Connects two points with a straight line.
• quadraticCurveTo: Connects three points with a quadratic curve.
• bezierCurveTo: Connects four points with a cubic Bézier curve.

Using bezierCurveTo for every four points can lead to sharp kinks at each interval.

Approximation Method: Interpolated Midpoints

A practical solution is to "curve to" the midpoints of three consecutive sample points, creating a continuous, smooth curve:

<code class="javascript">// move to the first point
ctx.moveTo(points[0].x, points[0].y);

for (var i = 1; i < points.length - 2; i++)
{
    var xc = (points[i].x + points[i + 1].x) / 2;
    var yc = (points[i].y + points[i + 1].y) / 2;
    ctx.quadraticCurveTo(points[i].x, points[i].y, xc, yc);
}

// curve through the last two points
ctx.quadraticCurveTo(points[i].x, points[i].y, points[i+1].x, points[i+1].y);</code>

This method approximates the curve by creating control points located at the midpoints between the actual sample points, ensuring a smooth transition at the end points.

Note:

This method doesn't draw a curve through every sample point, but it produces a visually seamless curve that closely approximates the desired shape. Alternative methods that connect through each point exist but are more complex to implement.

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