CGContextSetLineWidth(context, 1) - the width is almost alwayas at least 2 pixels instead 1

Question

With `CGContextSetLineWidth(context, 1)` the width is almost alwayas at least 2 pixels instead 1 QQCandleStickLayer.m ``` -(id)init { self = [super init]; if(self != nil) { self.delegate = self; self.opaque = NO; } return self; } - (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context{ CGContextSetLineWidth(context, 1.0f); CGContextSetAllowsAntialiasing(context, false); CGContextSetShouldAntialias(context, false); CGContextSetInterpolationQuality(context,kCGInterpolationNone); CGContextSetShadowWithColor(context, CGSizeMake( 0.0, 0.0 ), 0, NULL); CGContextMoveToPoint(context, self.bounds.origin.x+30.5f, self.bounds.origin.y+self.bounds.size.height-indent); CGContextAddLineToPoint(context, self.bounds.origin.x+30.5f, self.bounds.origin.y+self.bounds.size.height-(self.bounds.size.height-lastY)); CGContextClosePath(context); CGContextSetRGBStrokeColor(context, 119.0f/255, 119.0f/255, 119.0f/255, 1.0); CGContextStrokePath(context); } ``` QQDefluviumLayer.m ``` - (void)drawLayer:…

Accepted Answer

The line width is indeed 1 pixel wide, but 0.5 pixel wide on one side and 0.5 pixel wide on the other side. Sticking it to the pixel grids makes appears to be 1 pixel wide at 50% opacity on both sides, making it a 2 pixel wide line at 50% opacity.

To avoid this, draw the line on half-pixel coordinates.

For example, instead of

```
CGContextMoveToPoint(ctx, 20.0f, 30.0f);
CGContextAddLineToPoint(ctx, 20.0f, 100.0f);
```

do

```
CGContextMoveToPoint(ctx, 20.5f, 30.0f);
CGContextAddLineToPoint(ctx, 20.5f, 100.0f);
```

CGContextSetLineWidth(context, 1) - the width is almost alwayas at least 2 pixels instead 1

Solution

Problem