html5-canvas Navigating along a Path Trim bezier curve.

Example

This example show you how to trim a bezier.

The function trimBezier trims the ends off of the curve returning the curve fromPos to toPos. fromPos and toPos are in the range 0 to 1 inclusive, It can trim quadratic and cubic curves. The curve type is determined by the last x argument x4. If not undefined or null then it assumes the curve is cubic else the curve is a quadratic

The trimmed curve is returned as an array of points. 6 points for quadratic curves and 8 for cubic curves.

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Example Usage

Trimming a quadratic curve.

var p1 = {x : 10 , y : 100};
var p2 = {x : 100, y : 200};
var p3 = {x : 200, y : 0};
var newCurve = splitCurveAt(0.25, 0.75, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y)

var i = 0;
var p = newCurve
// Draw the trimmed curve
// Assumes ctx is canvas 2d context
ctx.lineWidth = 1;
ctx.strokeStyle = "black";
ctx.beginPath();
ctx.moveTo(p[i++],p[i++]);
ctx.quadraticCurveTo(p[i++], p[i++], p[i++], p[i++]);
ctx.stroke();

Trimming a cubic curve.

var p1 = {x : 10 , y : 100};
var p2 = {x : 100, y : 200};
var p3 = {x : 200, y : 0};
var p4 = {x : 300, y : 100};
var newCurve = splitCurveAt(0.25, 0.75, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y, p4.x, p4.y)

var i = 0;
var p = newCurve
// Draw the trimmed curve
// Assumes ctx is canvas 2d context
ctx.lineWidth = 1;
ctx.strokeStyle = "black";
ctx.beginPath();
ctx.moveTo(p[i++],p[i++]);
ctx.bezierCurveTo(p[i++], p[i++], p[i++], p[i++], p[i++], p[i++]);
ctx.stroke();

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Example Function

trimBezier = function(fromPos, toPos, x1, y1, x2, y2, x3, y3, [x4, y4])

Note: Arguments inside [x4, y4] are optional.

Note: This function requires the function in the example Split Bezier Curves At in this section

var trimBezier = function(fromPos, toPos, x1, y1, x2, y2, x3, y3, x4, y4){
    var quad, i, s, retBez;
    quad = false;
    if(x4 === undefined || x4 === null){
        quad = true;  // this is a quadratic bezier    
    }
    if(fromPos > toPos){ // swap is from is after to
        i = fromPos;
        fromPos = toPos
        toPos = i;
    }
    // clamp to on the curve
    toPos = toPos <= 0 ? 0 : toPos >= 1 ? 1 : toPos;
    fromPos = fromPos <= 0 ? 0 : fromPos >= 1 ? 1 : fromPos;
    if(toPos === fromPos){
        s = splitBezierAt(toPos, x1, y1, x2, y2, x3, y3, x4, y4);
        i = quad ? 4 : 6;
        retBez = [s[i], s[i+1], s[i], s[i+1], s[i], s[i+1]];
        if(!quad){
            retBez.push(s[i], s[i+1]);
        }
        return retBez;
    }
    if(toPos === 1 && fromPos === 0){       // no trimming required
        retBez = [x1, y1, x2, y2, x3, y3];  // return original bezier
        if(!quad){
            retBez.push(x4, y4);
        }
        return retBez;
    }
    if(fromPos === 0){
        if(toPos < 1){
            s = splitBezierAt(toPos, x1, y1, x2, y2, x3, y3, x4, y4);
            i = 0;
            retBez = [s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]];
            if(!quad){
                retBez.push(s[i++], s[i++]);
            }
        }
        return retBez;
    }
    if(toPos === 1){
        if(fromPos < 1){
            s = splitBezierAt(toPos, x1, y1, x2, y2, x3, y3, x4, y4);
            i = quad ? 4 : 6;
            retBez = [s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]];
            if(!quad){
                retBez.push(s[i++], s[i++]);
            }
        }
        return retBez;
    }
    s = splitBezierAt(fromPos, x1, y1, x2, y2, x3, y3, x4, y4);
    if(quad){
        i = 4;
        toPos = (toPos - fromPos) / (1 - fromPos);
        s = splitBezierAt(toPos, s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]);
        i = 0;
        retBez = [s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]];
        return retBez;
        
    }
    i = 6;
    toPos = (toPos - fromPos) / (1 - fromPos);
    s = splitBezierAt(toPos, s[i++], s[i++], s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]);
    i = 0;
    retBez = [s[i++], s[i++], s[i++], s[i++], s[i++], s[i++], s[i++], s[i++]];
    return retBez;
}