CALayer drawInContext can't draw 1px lines on retina displays

I want to draw double colored line with 1px lines of 2 different colors. I have a lot of code so I'm putting it after trying to explain.

If I use uiview drawRect method it works fine when I switch off antialiasing but when I use layer's drawLayerInContext it either displays one plain line, or 2 plain line lines of 2px with antialiasing off or two half transparent lines of 2px with antialising on.

I managed to get a similar behavior than UIView's drawRect method by creating an image with a custom context where I can specify a scale:

UIGraphicsBeginImageContextWithOptions([self bounds].size, NO, 0.f); // 0.f for scale means "scale for device's main screen".

I would just like to know why I don't get the same behavior in drawInContext and if there was a way to get similar behavior.

Here is the code that draws the double color line:

void DRAW_DOUBLE_LINE(CGContextRef ctx, CGPoint startPoint, CGPoint endPoint, UIColor* topColor, UIColor* bottomColor)
{
    UIGraphicsPushContext(ctx);

    UIBezierPath *topLine = [[UIBezierPath alloc] init];
    CGPoint topLineStartPoint = startPoint;
    CGPoint topLineEndPoint = endPoint;
    [topLine moveToPoint:topLineStartPoint];
    [topLine addLineToPoint:topLineEndPoint];
    [topColor setStroke];
    topLine.lineWidth = 0.5;
    [topLine stroke];

    UIBezierPath *bottomLine = [[UIBezierPath alloc] init];
    CGPoint bottomLineStartPoint = topLineStartPoint;
    bottomLineStartPoint.y +=0.5;
    CGPoint bottomLineEndPoint = topLineEndPoint;
    bottomLineEndPoint.y +=0.5;
    [bottomLine moveToPoint:bottomLineStartPoint];
    [bottomLine addLineToPoint:bottomLineEndPoint];
    [bottomColor setStroke];
    bottomLine.lineWidth = 0.5;
    [bottomLine stroke];

    UIGraphicsPopContext();
}

With the drawRect method of UIView I obtain this:

| Points y coordinate | A