画线问题

Question

brushSize=1.0f;
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)]; //originally self.frame.size.width, self.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapButt); //kCGLineCapSquare, kCGLineCapButt, kCGLineCapRound
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brushSize);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 0.0, 1.0);
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x+brushSize*4,lastPoint.y-brushSize);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x-brushSize, lastPoint.y+brushSize*4);
CGContextStrokePath(UIGraphicsGetCurrentContext());
CGContextFlush(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

我正在使用此代码绘图......在touchesmoved。

当我快速画画时，我确实会出现差距...该怎么做？

Answer 1

您应该使用UITouch的previousLocationInView:方法获取您手指上的先前已知点，并在该点与当前位置之间画一条线。

另一种解决方案是将currentPoint保持在两次调用之间的静态变量中。

Answer 2

CGContextBeginPath(Mycontext);
CGContextMoveToPoint(Mycontext, lastPoint.x, lastPoint.y);

int x, cx, deltax, xstep,y, cy, deltay, ystep,error, st, dupe;
int x0, y0, x1, y1;

x0 = currentPoint.x;
y0 = currentPoint.y;
x1 = lastPoint.x;
y1 = lastPoint.y;

// find largest delta for pixel steps
st = (abs(y1 - y0) > abs(x1 - x0));

// if deltay > deltax then swap x,y
if (st) {
(x0 ^= y0); (y0 ^= x0); (x0 ^= y0); // swap(x0, y0);
(x1 ^= y1); (y1 ^= x1); (x1 ^= y1); // swap(x1, y1);
}

deltax = abs(x1 - x0);
deltay = abs(y1 - y0);
error = (deltax / 2);
y = y0;

if (x0 > x1) { xstep = -1; }
else { xstep = 1; }

if (y0 > y1) { ystep = -1; }
else { ystep = 1; }

for ((x = x0); (x != (x1 + xstep)); (x += xstep))
{
(cx = x); (cy = y); // copy of x, copy of y

// if x,y swapped above, swap them back now
if (st) { (cx ^= cy); (cy ^= cx); (cx ^= cy); }

(dupe = 0); // initialize no dupe

if(!dupe) {
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), cx+brushSize*4,cy-brushSize);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), cx-brushSize, cy+brushSize*4);

}

(error -= deltay); // converge toward end of line

if (error < 0) { // not done yet
(y += ystep);
(error += deltax);
}
}

CGContextStrokePath(Mycontext);
Image_Cookie.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

lastPoint = currentPoint;