我正在查找此图像Expected Result
中的输出我需要勾画一下中风。我的代码如下
- (void)awakeFromNib {
self.strokeArray = [NSMutableArray array];
self.layerIndex = 0;
self.isSolid = false;
self.path = [[UIBezierPath alloc] init];
self.innerPath = [[UIBezierPath alloc] init];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[self.path moveToPoint:p];
[self.innerPath moveToPoint:p];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[self.path addLineToPoint:p];
[self.innerPath addLineToPoint:p];
[self setNeedsDisplay];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[self.path addLineToPoint:p];
[self.innerPath addLineToPoint:p];
[self drawBitmap];
[self setNeedsDisplay];
[self.path removeAllPoints];
[self.innerPath removeAllPoints];
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
[self touchesEnded:touches withEvent:event];
}
- (void)drawRect:(CGRect)rect
{
[self.incrementalImage drawInRect:rect];
[self.brushColor setStroke];
self.path.lineWidth = self.brushWidth;
if(self.isEraser)
[self.path strokeWithBlendMode:kCGBlendModeClear alpha:0.0];
else
[self.path stroke];
self.innerPath.lineWidth = self.brushWidth - 10;
[[UIColor clearColor] setStroke];
[self.innerPath strokeWithBlendMode:kCGBlendModeClear alpha:1.0];
}
- (void)drawBitmap
{
UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
if (!self.incrementalImage)
{
CGContextClearRect(context, CGRectMake(0,0,self.bounds.size.width,self.bounds.size.height));
}
[self.incrementalImage drawAtPoint:CGPointZero];
[self.brushColor setStroke];
self.path.lineWidth = self.brushWidth;
if(self.isEraser)
[self.path strokeWithBlendMode:kCGBlendModeClear alpha:0.0];
else
[self.path stroke];
self.innerPath.lineWidth = self.brushWidth - 10;
[[UIColor clearColor] setStroke];
[self.innerPath strokeWithBlendMode:kCGBlendModeClear alpha:1.0];
self.incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
在屏幕上我得到的是这张图片，Actual Result
我理解混合模式＆＃39;清除＆＃39;给人一种橡皮擦的效果。我想要的是，笔划的两侧应有一个坚实的轮廓，中间应清晰。它不应该融入它下面的路径。它下面的路径应该仍然是可见的。 我怎样才能达到这个结果？
答案 0 :(得分：3)
看一下这个问题：Generate a CGPath from another path's line width outline
我想你需要的是：创建一条线的多边形，而不是线条。使用CGPathCreateCopyByStrokingPath获取多边形的路径并对其进行描边。
好的，因为CGPathCreateCopyByStrokingPath似乎有点bug，你可以创建自己的实现。类似于以下算法，假设您在NSArray个对象中包含CGPoint个NSValue。
它很好用，直到你开始添加短的重叠线，这当然可以在绘图时轻松发生。您可以通过仅将touchesMoved中具有较大距离（lineWidth / 2？）的点添加到先前添加的点来减少此效果。另一个缺点是线条很直（没有kCGLineJoinRound或kCGLineCapRound），但也许你可以调整算法来做到这一点。
+ (UIBezierPath*)polygonForLine:(NSArray *)points withLineWidth:(CGFloat)lineWidth{
UIBezierPath *path = [UIBezierPath bezierPath];
//stores the starting point to close the path
CGPoint startPoint;
//get the points to a c-array for easier access
CGPoint cpoints[points.count];
int numPoints = 0;
for(NSValue *v in points){
cpoints[numPoints++] = [v CGPointValue];
}
//store the last intersection to apply it for the next segement
BOOL hasIntersection = NO;
CGPoint intersectionPoint;
for (int i=0;i<numPoints-1;i++){
//get the current line segment
CGPoint p1 = cpoints[i];
CGPoint p2 = cpoints[i+1];
CGPoint l1p1,l1p2;
getOffsetLineSegmentForPoints(p1,p2,lineWidth,&l1p1,&l1p2);
//if there had been an intersection with the previous segement, start here to get a nice outline
if(hasIntersection){
l1p1 = intersectionPoint;
}
//is there a next segment?
if(i+2<numPoints){
//get the next line segment
p1 = cpoints[i+1];
p2 = cpoints[i+2];
CGPoint l2p1,l2p2;
getOffsetLineSegmentForPoints(p1,p2,lineWidth,&l2p1,&l2p2);
//calculate the intersection point with the current line segment
hasIntersection = getLineIntersection(l1p1, l1p2, l2p1, l2p2, &intersectionPoint);
//if they intersect, the current linesegment has to end here to get a nice outline
if(hasIntersection){
l1p2 = intersectionPoint;
}
}
//write the current linesegment to the path
if(i==0){
//first point, move to it and store it for closing the path later on
startPoint = l1p1;
[path moveToPoint:startPoint];
}else{
[path addLineToPoint:l1p1];
}
[path addLineToPoint:l1p2];
}
//now do the same for the other side of the future polygon
hasIntersection = NO;//reset intersections
for (int i=numPoints-1;i>0;i--){
//get the current line segment
CGPoint p1 = cpoints[i];
CGPoint p2 = cpoints[i-1];
CGPoint l1p1,l1p2;
getOffsetLineSegmentForPoints(p1,p2,lineWidth,&l1p1,&l1p2);
//if there had been an intersection with the previous segement, start here to get a nice outline
if(hasIntersection){
l1p1 = intersectionPoint;
}
//is there a next segment?
if(i-2>=0){
//get the next line segment
p1 = cpoints[i-1];
p2 = cpoints[i-2];
CGPoint l2p1,l2p2;
getOffsetLineSegmentForPoints(p1,p2,lineWidth,&l2p1,&l2p2);
//calculate the intersection point with the current line segment
hasIntersection = getLineIntersection(l1p1, l1p2, l2p1, l2p2, &intersectionPoint);
//if they intersect, the current linesegment has to end here to get a nice outline
if(hasIntersection){
l1p2 = intersectionPoint;
}
}
//write the current linesegment to the path
[path addLineToPoint:l1p1];
[path addLineToPoint:l1p2];
}
//close the path
[path addLineToPoint:startPoint];
//we're done
return path;
}
void getOffsetLineSegmentForPoints(CGPoint p1, CGPoint p2, CGFloat lineWidth, CGPoint *linep1, CGPoint *linep2){
CGPoint offset = CGPointSub(p2, p1);
offset = CGPointNorm(offset);
offset = CGPointOrthogonal(offset);
offset = CGPointMultiply(offset, lineWidth/2);
(*linep1) = CGPointAdd(p1, offset);
(*linep2) = CGPointAdd(p2, offset);
}
CGPoint CGPointSub(CGPoint p1, CGPoint p2){
return CGPointMake(p1.x-p2.x, p1.y-p2.y);
}
CGPoint CGPointAdd(CGPoint p1, CGPoint p2){
return CGPointMake(p1.x+p2.x, p1.y+p2.y);
}
CGFloat CGPointLength(CGPoint p){
return sqrtf(powf(p.x,2)+powf(p.y,2));
}
CGPoint CGPointNorm(CGPoint p){
CGFloat length = CGPointLength(p);
if(length==0)
return CGPointZero;
return CGPointMultiply(p, 1/length);
}
CGPoint CGPointMultiply(CGPoint p, CGFloat f){
return CGPointMake(p.x*f, p.y*f);
}
CGPoint CGPointOrthogonal(CGPoint p){
return CGPointMake(p.y, -p.x);
}
BOOL getLineIntersection(CGPoint l1p1, CGPoint l1p2, CGPoint l2p1,
CGPoint l2p2, CGPoint *intersection)
{
CGPoint s1 = CGPointSub(l1p2, l1p1);
CGPoint s2 = CGPointSub(l2p2, l2p1);
float determinant = (-s2.x * s1.y + s1.x * s2.y);
if(determinant==0)
return NO;
CGPoint l2p1l1p1 = CGPointSub(l1p1, l2p1);
float s, t;
s = (-s1.y * l2p1l1p1.x + s1.x * l2p1l1p1.y) / determinant;
t = ( s2.x * l2p1l1p1.y - s2.y * l2p1l1p1.x) / determinant;
if (s >= 0 && s <= 1 && t >= 0 && t <= 1){
if (intersection != NULL){
(*intersection).x = l1p1.x + (t * s1.x);
(*intersection).y = l1p1.y + (t * s1.y);
}
return YES;
}
return NO;
}