Ios 为什么 UIBezierPath 比 Core Graphics 路径快

您说得对，UIBezierPath只是Core Graphics的Objective-c包装器，因此性能相当.不同之处(以及性能差值的原因)在于直接绘制CGPath时的CGContext状态与设置为UIBezierPath时的状态有很大不同.如果您查看UIBezierPath，它有以下设置:

• lineWidth，
• lineJoinStyle，
• lineCapStyle，
• miterLimit和
• flatness个

在判断对[path stroke]的调用(反汇编)时，您会注意到，在执行CGContextStrokePath调用之前，它会根据这些先前的值配置当前图形上下文.如果您在绘制CGPath之前执行相同的操作，它将执行相同的操作:

- (void)drawRect:(CGRect)rect
{
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    // Create the two paths, cgpath and uipath.
    CGMutablePathRef cgpath = CGPathCreateMutable();
    CGPathMoveToPoint(cgpath, NULL, 0, 100);

    UIBezierPath *uipath = [[UIBezierPath alloc] init];
    [uipath moveToPoint:CGPointMake(0, 200)];

    // Add 200 curve segments to each path.
    int iterations = 80000;
    CGFloat cgBaseline = 100;
    CGFloat uiBaseline = 200;
    CGFloat xincrement = self.bounds.size.width / iterations;
    for (CGFloat x1 = 0, x2 = xincrement;
         x2 < self.bounds.size.width;
         x1 = x2, x2 += xincrement)
    {
        CGPathAddCurveToPoint(cgpath, NULL, x1, cgBaseline-50, x2, cgBaseline+50, x2, cgBaseline);
        [uipath addCurveToPoint:CGPointMake(x2, uiBaseline)
                  controlPoint1:CGPointMake(x1, uiBaseline-50)
                  controlPoint2:CGPointMake(x2, uiBaseline+50)];
    }
    [[UIColor blackColor] setStroke];
    CGContextAddPath(ctx, cgpath);

    // Stroke each path
    CGContextSaveGState(ctx); {
        // configure context the same as uipath
        CGContextSetLineWidth(ctx, uipath.lineWidth);
        CGContextSetLineJoin(ctx, uipath.lineJoinStyle);
        CGContextSetLineCap(ctx, uipath.lineCapStyle);
        CGContextSetMiterLimit(ctx, uipath.miterLimit);
        CGContextSetFlatness(ctx, uipath.flatness);
        [self strokeContext:ctx];
        CGContextRestoreGState(ctx);
    }
    [self strokeUIBezierPath:uipath];

    [uipath release];
    CGPathRelease(cgpath);
}

- (void)strokeContext:(CGContextRef)context
{
    CGContextStrokePath(context);
}

- (void)strokeUIBezierPath:(UIBezierPath*)path
{
    [path stroke];
}

来自Instruments的快照: