html5-canvas Navigating along a Path Finding points along a cubic Bezier curve
Example
This example finds an array of approximately evenly spaced points along a cubic Bezier curve.
It decomposes Path segments created with context.bezierCurveTo into points along that curve.
// Return: an array of approximately evenly spaced points along a cubic Bezier curve
//
// Attribution: Stackoverflow's @Blindman67
// Cite: http://stackoverflow.com/questions/36637211/drawing-a-curved-line-in-css-or-canvas-and-moving-circle-along-it/36827074#36827074
// As modified from the above citation
//
// ptCount: sample this many points at interval along the curve
// pxTolerance: approximate spacing allowed between points
// Ax,Ay,Bx,By,Cx,Cy,Dx,Dy: control points defining the curve
//
function plotCBez(ptCount,pxTolerance,Ax,Ay,Bx,By,Cx,Cy,Dx,Dy){
var deltaBAx=Bx-Ax;
var deltaCBx=Cx-Bx;
var deltaDCx=Dx-Cx;
var deltaBAy=By-Ay;
var deltaCBy=Cy-By;
var deltaDCy=Dy-Cy;
var ax,ay,bx,by;
var lastX=-10000;
var lastY=-10000;
var pts=[{x:Ax,y:Ay}];
for(var i=1;i<ptCount;i++){
var t=i/ptCount;
ax=Ax+deltaBAx*t;
bx=Bx+deltaCBx*t;
cx=Cx+deltaDCx*t;
ax+=(bx-ax)*t;
bx+=(cx-bx)*t;
//
ay=Ay+deltaBAy*t;
by=By+deltaCBy*t;
cy=Cy+deltaDCy*t;
ay+=(by-ay)*t;
by+=(cy-by)*t;
var x=ax+(bx-ax)*t;
var y=ay+(by-ay)*t;
var dx=x-lastX;
var dy=y-lastY;
if(dx*dx+dy*dy>pxTolerance){
pts.push({x:x,y:y});
lastX=x;
lastY=y;
}
}
pts.push({x:Dx,y:Dy});
return(pts);
}
