xeravim - 1 year ago 115
Objective-C Question

# Create Bezier Curve in Objective C using Paul de Casteljau algorithm

I am trying to use Paul de Casteljau algorithm to draw Bezier Curve for my homework, but it seems it is not perfect, here are the codes

``````- (void)recursive_bezier :(double)x1 :(double)y1
:(double)x2 :(double)y2
:(double)x3 :(double)y3
:(double)x4 :(double)y4
{

count = count+1;
// Calculate all the mid-points of the line segments
//----------------------
double x12   = (x1 + x2) / 2;
double y12   = (y1 + y2) / 2;
double x23   = (x2 + x3) / 2;
double y23   = (y2 + y3) / 2;
double x34   = (x3 + x4) / 2;
double y34   = (y3 + y4) / 2;
double x123  = (x12 + x23) / 2;
double y123  = (y12 + y23) / 2;
double x234  = (x23 + x34) / 2;
double y234  = (y23 + y34) / 2;
double x1234 = (x123 + x234) / 2;
double y1234 = (y123 + y234) / 2;

if(isFlat)
{
//    // Draw and stop
//    //----------------------
[self drawLine:x1 :y1 :x4 :y4];

}
else
{
// Continue subdivision
//----------------------
if (count == 5) {
isFlat=true;
}

[self recursive_bezier:x1 :y1 :x12 :y12 :x123 :y123 :x1234 :y1234];
[self recursive_bezier:x1234 :y1234 :x234 :y234 :x34 :y34 :x4 :y4];

}
}

- (void)drawLine :(double)x1 :(double)y1
:(double)x4 :(double)y4{
countDraw = countDraw+1;
NSLog(@"============%d============",countDraw);
NSLog(@"x1 = %f y1 = %f",x1, y1);
NSLog(@"x4 = %f y4 = %f",x4, y4);

UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(x1, y1)];

CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = [path CGPath];
shapeLayer.strokeColor = [[UIColor blueColor] CGColor];
shapeLayer.lineWidth = 2.0;
shapeLayer.fillColor = [[UIColor clearColor] CGColor];

}``````

Can anyone help me why the right side not calculated and how to make the curve smooth?

ps : i got the algorithm on Bezier Curve Algorithm

The problem is that once `isFlat` is set to true, any further segments won't be subdivided properly, even at the top level. This is because it is information related to a specific level of the recursive calls and not something global to the whole thing. If you step through the execution of the code this should be more clear.
A better way to do it is to declare `count` as an int parameter to `recursive_bezier` and pass 0 at the top level when you call it, and pass `count + 1` when you call it recursively. You can get rid of the `isFlat` variable and just test for `count >= 5`.