我的问题与here中提到的问题相同。我在我的应用程序中也使用了两个图像,我只需要通过触摸擦除顶部图像。然后通过触摸取消擦除(如果需要)擦除部分。我正在使用以下代码擦除顶部图像。这种方法也存在问题。这是图像很大,我正在使用Aspect Fit内容模式来正确显示它们。 当我触摸屏幕时,它会在角落中擦除而不是触摸的位置。我认为触摸点计算需要一些修复。任何帮助将不胜感激。
第二个问题是如何通过触摸取消擦除已删除的部分?
UIGraphicsBeginImageContext(self.imgTop.image.size);
[self.imgTop.image drawInRect:CGRectMake(0, 0, self.imgTop.image.size.width, self.imgTop.image.size.height)];
self.frame.size.width, self.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
GContextSetLineWidth(UIGraphicsGetCurrentContext(), pinSize);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0, 0, 0, 1.0);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
self.imgTop.contentMode = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
答案 0 :(得分:7)
你的代码很模糊:你在里面用 imgTop 创建一个上下文,然后用kCGBlendModeCopy
黑色混合?这会导致黑色被复制到 imgTop 上。我假设你想设置图层的content
属性呢?
无论如何,这门课做你需要的。只有一些有趣的方法(它们位于顶部),其他方法只是属性或init...
例程。
@interface EraseImageView : UIView {
CGContextRef context;
CGRect contextBounds;
}
@property (nonatomic, retain) UIImage *backgroundImage;
@property (nonatomic, retain) UIImage *foregroundImage;
@property (nonatomic, assign) CGFloat touchWidth;
@property (nonatomic, assign) BOOL touchRevealsImage;
- (void)resetDrawing;
@end
@interface EraseImageView ()
- (void)createBitmapContext;
- (void)drawImageScaled:(UIImage *)image;
@end
@implementation EraseImageView
@synthesize touchRevealsImage=_touchRevealsImage, backgroundImage=_backgroundImage, foregroundImage=_foregroundImage, touchWidth=_touchWidth;
#pragma mark - Main methods -
- (void)createBitmapContext
{
// create a grayscale colorspace
CGColorSpaceRef grayscale=CGColorSpaceCreateDeviceGray();
/* TO DO: instead of saving the bounds at the moment of creation,
override setFrame:, create a new context with the right
size, draw the previous on the new, and replace the old
one with the new one.
*/
contextBounds=self.bounds;
// create a new 8 bit grayscale bitmap with no alpha (the mask)
context=CGBitmapContextCreate(NULL,
(size_t)contextBounds.size.width,
(size_t)contextBounds.size.height,
8,
(size_t)contextBounds.size.width,
grayscale,
kCGImageAlphaNone);
// make it white (touchRevealsImage==NO)
CGFloat white[]={1., 1.};
CGContextSetFillColor(context, white);
CGContextFillRect(context, contextBounds);
// setup drawing for that context
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineJoin(context, kCGLineJoinRound);
CGColorSpaceRelease(grayscale);
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch=(UITouch *)[touches anyObject];
// the new line that will be drawn
CGPoint points[]={
[touch previousLocationInView:self],
[touch locationInView:self]
};
// setup width and color
CGContextSetLineWidth(context, self.touchWidth);
CGFloat color[]={(self.touchRevealsImage ? 1. : 0.), 1.};
CGContextSetStrokeColor(context, color);
// stroke
CGContextStrokeLineSegments(context, points, 2);
[self setNeedsDisplay];
}
- (void)drawRect:(CGRect)rect
{
if (self.foregroundImage==nil || self.backgroundImage==nil) return;
// draw background image
[self drawImageScaled:self.backgroundImage];
// create an image mask from the context
CGImageRef mask=CGBitmapContextCreateImage(context);
// set the current clipping mask to the image
CGContextRef ctx=UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
CGContextClipToMask(ctx, contextBounds, mask);
// now draw image (with mask)
[self drawImageScaled:self.foregroundImage];
CGContextRestoreGState(ctx);
CGImageRelease(mask);
}
- (void)resetDrawing
{
// draw black or white
CGFloat color[]={(self.touchRevealsImage ? 0. : 1.), 1.};
CGContextSetFillColor(context, color);
CGContextFillRect(context, contextBounds);
[self setNeedsDisplay];
}
#pragma mark - Helper methods -
- (void)drawImageScaled:(UIImage *)image
{
// just draws the image scaled down and centered
CGFloat selfRatio=self.frame.size.width/self.frame.size.height;
CGFloat imgRatio=image.size.width/image.size.height;
CGRect rect={0.,0.,0.,0.};
if (selfRatio>imgRatio) {
// view is wider than img
rect.size.height=self.frame.size.height;
rect.size.width=imgRatio*rect.size.height;
} else {
// img is wider than view
rect.size.width=self.frame.size.width;
rect.size.height=rect.size.width/imgRatio;
}
rect.origin.x=.5*(self.frame.size.width-rect.size.width);
rect.origin.y=.5*(self.frame.size.height-rect.size.height);
[image drawInRect:rect];
}
#pragma mark - Initialization and properties -
- (id)initWithCoder:(NSCoder *)aDecoder
{
if ((self=[super initWithCoder:aDecoder])) {
[self createBitmapContext];
_touchWidth=10.;
}
return self;
}
- (id)initWithFrame:(CGRect)frame
{
if ((self=[super initWithFrame:frame])) {
[self createBitmapContext];
_touchWidth=10.;
}
return self;
}
- (void)dealloc
{
CGContextRelease(context);
[super dealloc];
}
- (void)setBackgroundImage:(UIImage *)value
{
if (value!=_backgroundImage) {
[_backgroundImage release];
_backgroundImage=[value retain];
[self setNeedsDisplay];
}
}
- (void)setForegroundImage:(UIImage *)value
{
if (value!=_foregroundImage) {
[_foregroundImage release];
_foregroundImage=[value retain];
[self setNeedsDisplay];
}
}
- (void)setTouchRevealsImage:(BOOL)value
{
if (value!=_touchRevealsImage) {
_touchRevealsImage=value;
[self setNeedsDisplay];
}
}
@end
一些注意事项:
此课程会保留您需要的两张图片。它具有touchRevealsImage
属性,可将模式设置为绘图或擦除,您可以设置线条的宽度。
在初始化时,它会创建一个CGBitmapContextRef
,灰度,8bpp,无alpha,视图大小相同。此上下文用于存储将应用于前景图像的蒙版。
每次在屏幕上移动手指时,使用CoreGraphics在CGBitmapContextRef
上绘制一条线,白色显示图像,黑色隐藏它。通过这种方式我们存储了一个黑白绘图。
drawRect:
例程只是绘制背景,然后从CGImageRef
创建CGBitmapContextRef
并将其作为掩码应用于当前上下文。然后绘制前景图像。要绘制图像,它使用- (void)drawImageScaled:(UIImage *)image
,它只绘制缩放和居中的图像。
如果您计划调整视图大小,则应实现一种方法来复制或重新创建具有新大小的掩码,覆盖- (void)setFrame:(CGRect)frame
。
- (void)reset
方法只是清除蒙版。
即使位图上下文没有任何alpha通道,使用的灰度色彩空间也有 alpha:这就是为什么每次设置一个颜色时,我都必须指定两个组件。 / p>