在UIView或GLKView上绘制？

Question

I need to draw a separator line with some dots on it. I have decided I will do this using the draw method, as opposed to including images of the separator. I will do this for performance and for customisability, as the separator changes sometimes.

Now I have looked into the draw() method on UIView and I have noticed that Apple suggests using GLKView when drawing using OpenGL.

For a simple separator, won't it be too much of a hassle to call OpenGL? Or is the OpenGL overhead negligible? When would I want to use the native UIKit draw() then?

FYI I don't know either method, but want to learn both methods, so don't reply "what you know best". I am simply asking about performance.

Answer 1

OpenGL uses GPU instead of CPU for computation. If you are making something like a gaming app, then you can think of using OpenGL. I believe you want to draw a line in an iOS App. For that you can either use drawRect method in UIView or create a shapeLayer and add it as a sublayer.

The following examples will show you:

CAShapeLayer *simpleLine = [CAShapeLayer layer];
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(0, 80)];
[path addLineToPoint:CGPointMake(300, 80)];
simpleLine.lineWidth = 1.0;
simpleLine.path = path.CGPath;
simpleLine.strokeColor = [[UIColor blackColor] CGColor];
[[self.view layer] addSublayer:simpleLine];

For using drawRect , you are supposed to do this inside a Custom UIView as opposed to the above method.

- (void)drawRect:(CGRect)rect {
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, 80)];
    [path addLineToPoint:CGPointMake(300, 80)];
    path.lineWidth = 1.0;
    [[UIColor blueColor] setStroke];
    [path stroke];
}

If your separator parameters changes and if you are making an app, it's better to use drawRect method. You can call this method anytime by using [CustomUIView setNeedsDisplay:YES]

Edit

What you're asking for is circle over line. You can do that by drawing UIBezierPath for line first and then add UIBezierPath for circle later.

Answer 2

Normal Line

UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(10.0, 10.0)];
[path addLineToPoint:CGPointMake(100.0, 100.0)];
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = [path CGPath];
shapeLayer.strokeColor = [[UIColor redColor] CGColor];
shapeLayer.lineWidth = 3.0;
shapeLayer.fillColor = [[UIColor clearColor] CGColor];
[self.view.layer addSublayer:shapeLayer];

Dotted Line

UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(10.0, 10.0)];
[path addLineToPoint:CGPointMake(100.0, 100.0)];
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = [path CGPath];
shapeLayer.strokeColor = [[UIColor redColor] CGColor];
shapeLayer.lineWidth = 3.0;
shapeLayer.fillColor = [[UIColor clearColor] CGColor];
shapeLayer.lineDashPattern = @[@4, @2];
[self.view.layer addSublayer:shapeLayer];