iOS 画笔轨迹优化

iOS 画笔轨迹优化

一 、常规画法

- (void)draw_draw:(CGPoint *)points context:(CGContextRef)context count:(NSInteger)count {
    CGContextFillPath(context);
    CGContextAddLines(context, points, count);//添加线
    CGContextDrawPath(context, kCGPathStroke); //根据坐标绘制路径
}

二、优化方式一

static CGPoint midPointForPoints(CGPoint p1, CGPoint p2) {
    return CGPointMake((p1.x + p2.x) / 2.0, (p1.y + p2.y) / 2.0);
}

- (UIBezierPath *)draw_quadCurvedPathWithPoints:(NSArray *)points {
    CGPoint currentPoint = [points[0] CGPointValue];
    CGPoint previousPoint = currentPoint;

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:currentPoint];
    
    if (points.count == 2) {
        CGPoint p2 = [points[1] CGPointValue];
        [path addLineToPoint:p2];
        return path;
    }

    NSInteger count = [points count];
    
    for (int i = 1; i < count; i++) {
        currentPoint = [points[i] CGPointValue];
        CGPoint midPoint = midPointForPoints(previousPoint, currentPoint);
        [path addQuadCurveToPoint:midPoint controlPoint:previousPoint];
        previousPoint = currentPoint;
    }
    return path;
}

三、优化方式二

#define POINT(_INDEX_) [(NSValue *)[points objectAtIndex:_INDEX_] CGPointValue]
- (UIBezierPath *)draw_smoothedPathWithPoints:(NSArray *)pointsArray andGranularity:(NSInteger)granularity {
    NSMutableArray *points = [pointsArray mutableCopy];
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetAllowsAntialiasing(context, YES);
    
    UIBezierPath *smoothedPath = [UIBezierPath bezierPath];
    
    // Add control points to make the math make sense
    [points insertObject:[points objectAtIndex:0] atIndex:0];
    [points addObject:[points lastObject]];
    [smoothedPath moveToPoint:POINT(0)];
    
    for (NSUInteger index = 1; index < points.count - 2; index++) {
        CGPoint p0 = POINT(index - 1);
        CGPoint p1 = POINT(index);
        CGPoint p2 = POINT(index + 1);
        CGPoint p3 = POINT(index + 2);
        
        // now add n points starting at p1 + dx/dy up until p2 using Catmull-Rom splines
        for (int i = 1; i < granularity; i++) {
            
            float t = (float) i * (1.0f / (float) granularity);
            float tt = t * t;
            float ttt = tt * t;
            
            CGPoint pi; // intermediate point
            pi.x = 0.5 * (2*p1.x+(p2.x-p0.x)*t + (2*p0.x-5*p1.x+4*p2.x-p3.x)*tt + (3*p1.x-p0.x-3*p2.x+p3.x)*ttt);
            pi.y = 0.5 * (2*p1.y+(p2.y-p0.y)*t + (2*p0.y-5*p1.y+4*p2.y-p3.y)*tt + (3*p1.y-p0.y-3*p2.y+p3.y)*ttt);
            [smoothedPath addLineToPoint:pi];
        }
        // Now add p2
        [smoothedPath addLineToPoint:p2];
    }
    // finish by adding the last point
    [smoothedPath addLineToPoint:POINT(points.count - 1)];
    
    return smoothedPath;
}

经过对比上边方式一与方式二的差异不大；