在ios中從UIImage中刪除行

Question

我在UIImageView中有一個圖像。我已經成功地在圖像上畫出了線條。現在我想要刪除用戶將執行長按手勢的特定線條。我怎樣才能做到這一點 ？我的代碼是：

{

 // gets the location in the form of (x,y) coordinates 
     CGPoint location=[sender locationInView:imageView]; 
     // convetrs the location relative to the image 
     CGPoint contextLocation = CGPointMake(location.x*imageView.image.size.width/imageView.frame.size.width, location.y*imageView.image.size.height/imageView.frame.size.height); 
     // converts the location point into NSValue 
     NSValue *imagePoint=[NSValue valueWithCGPoint:contextLocation]; 
     // Adds the image into NSMutable Array 
     [imageLocations addObject:imagePoint]; 
     // color of line 
     UIColor * linearcolor=[UIColor blueColor]; 


     UIGraphicsBeginImageContext(imageView.image.size); 

     [imageView.image drawAtPoint:CGPointMake(0, 0)]; 


     CGContextRef context=UIGraphicsGetCurrentContext(); 

     // Brush widt 
     CGContextSetLineWidth(context, 3.0); 
     // Line Color 
     CGContextSetStrokeColorWithColor(context, [linearcolor CGColor]); 
     // Hard coded point for location 2 
     CGPoint location2=CGPointMake(300, 400); 


     CGContextMoveToPoint(context, contextLocation.x, contextLocation.y); 

     CGContextAddLineToPoint(context, location2.x, location2.y); 
     CGContextStrokePath(context); 

     newImage=UIGraphicsGetImageFromCurrentImageContext(); 

     UIGraphicsEndImageContext(); 
     imageView.image=newImage; 



    } 

Answer 1

你需要做的是找到行按下，並從你有點的數組中刪除它，然後用線條重畫整個圖像。

我想這個問題是如何找到正確的路線：

比方說你有從手勢得到一個位置L。然後，你需要的是通過所有的點對諸如

for(NSInteger i=0; i< imageLocations.count.count-1; i+=2) 
{ 
    CGPoint T1 = [imageLocations[i] CGPointValue]; 
    CGPoint T2 = [imageLocations[i+1] CGPointValue]; 
} 

遍歷現在你有了點L，T1，T2。從這裏有很多方法可以檢測線路是否被擊中。我最喜歡的是先用點積，看新聞是在年線附近，像這樣：

CGFloat dotValue = dot(normalized(T1-L), normalized(T2-L)) 

查找的點積點在線正常化的過程。現在dotValue應該接近-1被擊中的線。你應該使用類似if(dotValue > -.7f) continue;的東西來刪除沿着線路離印刷機太遠的所有線條。

接下來是實際找到點的距離。這實際上是一個跨產品的Z分量：

CGFloat crossValue = fabsf(cross((L-T1), normalized(T2-T1)).z); 

我知道你有沒有Z分量這樣使用：

crossValue = A.x*B.y - A.y*B.x 

所以，現在你擁有這一切的僞代碼應該是這樣的：

CGPoint L; 
NSInteger bestLineIndex = -1; 
CGFloat bestLineDistance = 10000.0f; // something large 

for (CGPoint T1, T2; NSInteger index) 
{ 
    dotValue = ... 
    if(dotValue < -.7) 
    { 
     crossValue = ... 
     if(crossValue < bestLineDistance) 
     { 
      bestLineDistance = crossValue; 
      bestLineIndex = index; 
     } 
    } 
} 

所以，你到底有哪些應該被刪除的第一行點的指數，如果不是-1（如果沒有-1行發現觸摸附近）。

對於使用交叉產品從三分線距離：

- (CGFloat)distanceBetweenPoint:(CGPoint)L andLineWithStart:(CGPoint)T1 end:(CGPoint)T2 
{ 
    CGPoint T1toL = CGPointMake(L.x-T1.x, L.y-T1.y); 
    CGPoint T2toL = CGPointMake(L.x-T2.x, L.y-T2.y); 

    CGFloat T2toLDistance = sqrt(T2toL.x*T2toL.x + T2toL.y*T2toL.y); 
    CGPoint T2toLNormalized = CGPointMake(T2toL.x/T2toLDistance, T2toL.y/T2toLDistance); 

    CGFloat zComponentOfCross = T1toL.x*T2toLNormalized.y - T1toL.y*T2toLNormalized.x; 

    return fabs(zComponentOfCross); 
} 

Answer 2

很簡單。我將下面的代碼添加爲您的問題。

// gets the location in the form of (x,y) coordinates 
    CGPoint location=[sender locationInView:imageView]; 
    // convetrs the location relative to the image 
    CGPoint contextLocation = CGPointMake(location.x*imageView.image.size.width/imageView.frame.size.width, location.y*imageView.image.size.height/imageView.frame.size.height); 
    // converts the location point into NSValue 
    NSValue *imagePoint=[NSValue valueWithCGPoint:contextLocation]; 
    // Adds the image into NSMutable Array 
    [imageLocations addObject:imagePoint]; 
    // color of line 
    UIColor * linearcolor=[UIColor blueColor]; 


    UIGraphicsBeginImageContext(imageView.image.size); 

    [imageView.image drawAtPoint:CGPointMake(0, 0)]; 


    CGContextRef context=UIGraphicsGetCurrentContext(); 

    // Brush widt 
    CGContextSetLineWidth(context, 3.0); 

    **CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);** 

    // Hard coded point for location 2 
    CGPoint location2=CGPointMake(300, 400); 


    CGContextMoveToPoint(context, contextLocation.x, contextLocation.y); 

    CGContextAddLineToPoint(context, location2.x, location2.y); 
    CGContextStrokePath(context); 

    newImage=UIGraphicsGetImageFromCurrentImageContext(); 

    UIGraphicsEndImageContext(); 
    imageView.image=newImage; 
} 

希望這對我有幫助。