如何捕捉沒有背景的畫布繪製簽名？

Question

現在我將繪製的簽名保存在畫布上作爲圖像，但只要我在UIImageView中顯示圖像，也會顯示白色背景。我不想用白色背景顯示它，我只是想顯示簽名。我怎樣才能做到這一點？

下面是一段代碼保存：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentsDirectory = [paths objectAtIndex:0]; // Get documents folder 
NSString *dataPath = [documentsDirectory stringByAppendingPathComponent:@"MyFolder"]; 
NSError *error = nil; 
if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath]) 
    [[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:&error]; 


CGSize size = self.view.bounds.size; 
CGRect cropRect = CGRectMake(10, 50, 640, 300); 

/* Get the entire on screen map as Image */ 
UIGraphicsBeginImageContext(size); 
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()]; 
UIImage * Image1 = UIGraphicsGetImageFromCurrentImageContext(); 

UIGraphicsEndImageContext(); 


/* Crop the desired region */ 
CGImageRef imageRef = CGImageCreateWithImageInRect(Image1.CGImage, cropRect); 
UIImage * cropImage = [UIImage imageWithCGImage:imageRef]; 
CGImageRelease(imageRef); 

UIGraphicsEndImageContext(); 

canvasImage.image = cropImage; 

//for saving image to documents directory 
NSArray *paths1 = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,  NSUserDomainMask, YES); 
NSString *documentsDirectory1 = [paths1 objectAtIndex:0]; 
NSString *savedImagePath1 = [documentsDirectory1 stringByAppendingPathComponent:@"MyFolder/signatureImage.png"]; 
UIImage *image = canvasImage.image; // imageView is my image from camera 
NSData *imageData = UIImagePNGRepresentation(cropImage); 
[imageData writeToFile:savedImagePath1 atomically:NO];  

Answer 1

1. 考慮您對您繪製的UIImageView。
2. 打開你想要的圖像編輯器，並製作一個圖像：它必須是完全白色和99％透明的。

爲什麼：如果圖像上下文是100％透明的，圖像上下文會遇到麻煩。所以你做一個白色的圖像，讓我們說99.9％透明，所以用戶的眼睛會看到一個透明的圖像，但目標C會看到一個「正常」的。

現在，這是我畫的簽名方式：

聲明的ivars：

UIImageView image_signature; 
CGPoint lastP; 

然後：

//___________________________________________________ 
-(void)drawLineFromX:(float)x fromY:(float)y toX:(float)xx toY:(float)yy{ 
    UIGraphicsBeginImageContext(image_signature.image.size); 
    [image_signature.image drawInRect:CGRectMake(0, 0, image_signature.image.size.width, image_signature.image.size.height)]; 
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); 
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0); 
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 0.0, 0.0, 1.0); 
    CGContextBeginPath(UIGraphicsGetCurrentContext()); 
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), x, y); 
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), xx, yy); 
    CGContextStrokePath(UIGraphicsGetCurrentContext()); 
    [image_signature setImage:UIGraphicsGetImageFromCurrentImageContext()]; 
    UIGraphicsEndImageContext(); 
} 
//___________________________________________________ 
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { 
    UITouch *touch = [touches anyObject]; 
    lastP = [touch locationInView:self.view]; 
    [button_authorize setEnabled:YES]; 

} 
//___________________________________________________ 
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{ 
    UITouch *touch = [touches anyObject]; 
    CGPoint nextP = [touch locationInView:image_signature]; 
    [self drawLineFromX:lastP.x fromY:lastP.y toX:nextP.x toY:nextP.y]; 
    lastP = nextP; 
} 
//___________________________________________________ 
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{ 
    UITouch *touch = [touches anyObject]; 
    CGPoint nextP = [touch locationInView:image_signature]; 
    //and this will allow you to draw a point, you know, some people 
    //use dots in their signatures   
    [self drawLineFromX:lastP.x fromY:lastP.y toX:nextP.x toY:nextP.y]; 
    lastP = nextP; 
} 

，並清除簽名（你有德魯）只需再次將99％的白色透明圖像加載到「image_signature」imageView