I am making a project on touch moved I want to change the alpha or visibility (whatever possible) of the image at the point where it is touched. Lets say Unhidethat particular point of image..
PS I already know how to erase the image. I am looking for unerase
I think this project does exactly what you're looking for : https://github.com/SebastienThiebaud/STScratchView
You have 2 images where one is the hidden image and the other one is the one that you scratch off.
Or even this project : http://www.cocoacontrols.com/platforms/ios/controls/scratch-n-see
I'm sorry for not having a good format for the code, for they are copied from my blog. It takes me a lot to edit.
When your finger moves, erase some parts :
- (UIImage *)erasePartsMoved {
UIImage *image = nil;
UIColor *color = [UIColor whiteColor];
CGFloat width = 5.0f;
CGSize imageContextSize = self.imageView.frame.size;
UIGraphicsBeginImageContext(imageContextSize);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, width);
CGContextSetStrokeColorWithColor(context, [color CGColor]);
CGContextMoveToPoint(context, self.touchStartPoint.x, self.touchStartPoint.y);
//Do something needed.
CGContextAddLineToPoint(context, self.touchEndPoint.x, self.touchEndPoint.y);
CGContextStrokePath(context);
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;}
Get the point touched, then calculate a circle with the touched point, and finally change the alpha of the pixels in the circle:
typedef struct _singleRGBA{
unsigned char red;
unsigned char green;
unsigned char blue;
unsigned char alpha;} RGBA;
To change the pixel's alpha :
void filterOpacity(UInt8 *pixelBuf, UInt32 offset, void *context){
double val = *((double*)context);
int a = offset+3;
int alpha = pixelBuf[a];
pixelBuf[a] = SAFECOLOR(alpha * val);}
I hope the above would do a favor. Funny question, I would like to do a runnable demo later.
I believe alpha is the property of the entire view so all you can do is draw on that particular point... refer this may be this is what you are trying to achieve.
- (void)viewDidLoad
{
//load super view
[super viewDidLoad];
//to decrease alpha.
UISwipeGestureRecognizer *swiperight=[[UISwipeGestureRecognizer alloc]
initWithTarget:self action: @selector(setalpha_decrease:)];
[swiperight setDirection:UISwipeGestureRecognizerDirectionRight];
[self.view addGestureRecognizer:swiperight];
//to increase alpha.
UISwipeGestureRecognizer *swipeleft=[[UISwipeGestureRecognizer alloc]
initWithTarget:self action: @selector(setalpha_increase:)];
[swipeleft setDirection:UISwipeGestureRecognizerDirectionLeft];
[self.view addGestureRecognizer:swipeleft];
}
-(void) setalpha_decrease:(UIPanGestureRecognizer *) gestureRecognizer {
imgview.alpha= imgtomove.alpha-(imgtomove.alpha/10);
}
-(void) setalpha_increase:(UIPanGestureRecognizer *) gestureRecognizer {
imgview.alpha= imgtomove.alpha+(imgtomove.alpha/10);
}
Why don't you put an empty view on top which is filled with a colour or texture and then using @AnkitSrivastava answer let the touch rub away parts of the view's background, revealing the hidden image behind.
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *t = [[touches allObjects] objectAtIndex:0];
float alpha = [t locationInView:self.view].x / self.view.frame.size.width;
_img.alpha = alpha;
}
