在 ios 中从 UIImage 中删除线条

Question

我在 UIImageView 中有一张图片。我在图像上画了线条 sucdcessfully.Now 我想删除用户将在其上执行长按手势的特定线条。我怎样才能做到这一点？我的代码是：

{

        // 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

很简单。我在下面添加我的代码作为您的问题。

// 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;
}

希望这是 helpful.Enjoy。

Answer 2

您需要做的是找到按下的线并将其从您拥有的点数组中删除，然后使用这些线重新绘制整个图像。

我想问题在于如何找到正确的行：

假设您有一个位置 L 从手势中获取。那么你需要的是遍历所有的点对如

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

现在您有积分 L、T1、T2。从这里开始，有很多方法可以检测线是否被击中。我最喜欢的是首先使用点积来查看印刷机是否在线附近，如下所示：

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

在网上找到点积和点归一化的程序。现在 dotValue 应该接近 -1 才能命中该行。你应该使用 if(dotValue > -.7f) continue; 之类的东西来删除所有离印刷机太远的线。

接下来就是实际求出点到线的距离。这实际上是一个叉积的 Z 分量：

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

我知道你没有 Z 组件所以使用：

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

所以现在你已经有了所有这些伪代码应该是这样的：

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;
        }
    }
}

所以最后你有第一条线点的索引，如果不是 -1（如果 -1 在触摸附近没有找到线），应该删除它。

对于使用叉积的点的直线距离：

- (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);
}

在 ios 中从 UIImage 中删除线条

Removing lines from UIImage in ios

ios

uiimageview

uiimage