Trim bezier curve.

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.

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();

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;
}

<!—- Please note anyone editing this example that it is dependent on the example Split Bezier Curves At. If you make changes to either example please ensure that they remain compatible. If you remove the dependent please provide a replacement function or remove this as well (and may you be infested with bugs) —–!>

Found a mistake? Have a question or improvement idea? Let me know.

Table Of Contents