保存CGContextRef

时间:2010-08-02 20:30:36

标签: objective-c uiview quartz-2d cgcontext

我有一个绘图应用程序,我想在其中创建一个撤消方法。绘图发生在TouchesMoved:方法中。

我正在尝试创建一个CGContextRef并将其推送到堆栈或将其保存在上下文属性中,以后可以恢复,但没有任何运气。任何建议都会很棒。这就是我的......

UIImageView      *drawingSurface;
CGContextRef       undoContext;


- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
 UIGraphicsBeginImageContext(self.view.frame.size);
 CGContextRef context = UIGraphicsGetCurrentContext();
 [drawingSurface.image drawInRect:CGRectMake(0, 0, drawingSurface.image.size.width, drawingSurface.image.size.height)]; 
 UIGraphicsPushContext(context);

        // also tried but cant figure how to restore it
        undoContext = context;

 UIGraphicsEndImageContext();
}

然后我有一个由我的撤销按钮触发的方法......

- (IBAction)restoreUndoImage {
 UIGraphicsBeginImageContext(self.view.frame.size);
 UIGraphicsPopContext();
 drawingSurface.image = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
}

当我运行它时,我相信我的drawingSurface被指定为nil,因为它只是删除了图像中的所有内容。

我的猜测是我无法使用pop并按此方式推送。但我似乎无法弄清楚如何只保存上下文然后将其推回到drawingSurface上。 Hmmmm。任何帮助都会......嗯......乐于助人。提前致谢 -

而且,仅供参考,这是我正在做的绘制到屏幕,这是很好的工作。这是我的TouchesMoved:

 UIGraphicsBeginImageContext(self.view.frame.size);
 CGContextRef context = UIGraphicsGetCurrentContext();
 [drawingSurface.image drawInRect:CGRectMake(0, 0, drawingSurface.image.size.width, drawingSurface.image.size.height)]; 

 CGContextSetLineCap(context, kCGLineCapRound); //kCGLineCapSquare, kCGLineCapButt, kCGLineCapRound
 CGContextSetLineWidth(context, self.brush.size); // for size

 CGContextSetStrokeColorWithColor (context,[currentColor CGColor]);

 CGContextBeginPath(context);
 CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
 CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
 CGContextStrokePath(context);
 drawingSurface.image = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();

1 个答案:

答案 0 :(得分:1)

我认为你正在以错误的方式处理这个问题并且混淆上下文。

在立即模式API中,您可以使用push / pop保存对象的“状态”,而不是图形表示。状态由线宽,颜色和位置组成。图形表示是绘制操作(位图)的结果,通常是您不想保存的内容。

而是尝试保存用于创建绘图的“信息”。

我最初的建议是将你的造型和绘画分开。在OSX上,您可以使用NSBezierPath,但对于iOS,我们必须使用点数组。

例如,鉴于此协议:

// ViewController.h
@protocol DrawSourceProtocol <NSObject>
- (NSArray*)pathsToDraw;
@end

@interface ViewController : UIViewController<DrawSourceProtocol>
@end

您可以实现以下功能:

// ViewController.m
@interface ViewController () {
  NSMutableArray *currentPath;  
  NSMutableArray *allPaths;
  MyView *view_;
}
@end

...

- (void)viewDidLoad {
  [super viewDidLoad];
  currentPath = [[NSMutableArray alloc] init];
  allPaths = [[NSMutableArray alloc] init];    
  view_ = (MyView*)self.view;
  view_.delegate = self;
}

- (NSArray*)pathsToDraw {  
  // Return the currently draw path too
  if (currentPath && currentPath.count) {
    NSMutableArray *allPathsPlusCurrent = [[NSMutableArray alloc] initWithArray:allPaths];
    [allPathsPlusCurrent addObject:currentPath];
    return allPathsPlusCurrent;
  }  
  return allPaths;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  currentPath = [[NSMutableArray alloc] init];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  // When a touch ends, save the current path
  [allPaths addObject:currentPath];
  currentPath = [[NSMutableArray alloc] init];
  [view_ setNeedsDisplay];    
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
  UITouch *touch = [touches anyObject];   
  CGPoint currentPoint = [touch locationInView:self.view];

  // We store the point with the help of NSValue
  [currentPath addObject:[NSValue valueWithCGPoint:currentPoint]];  

  // Update the view
  [view_ setNeedsDisplay];  
}

现在继承你的视图(我在这里称我的MyView)并实现类似这样的东西:

// MyView.h
#import "ViewController.h"

@protocol DrawSourceProtocol;

@interface MyView : UIView {
   __weak id<DrawSourceProtocol> delegate_; 
}
@property (weak) id<DrawSourceProtocol> delegate;
@end

// MyView.m

@synthesize delegate = delegate_;

...

- (void)drawRect:(CGRect)rect { 
  NSLog(@"Drawing!");

  // Setup a context
  CGContextRef context = UIGraphicsGetCurrentContext();   
  CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
  CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 1.0);
  CGContextSetLineWidth(context, 2.0);

  // Get the paths
  NSArray *paths = [delegate_ pathsToDraw];

  for (NSArray *aPath in paths) {
    BOOL firstPoint = TRUE;
    for (NSValue *pointValue in aPath) {
      CGPoint point = [pointValue CGPointValue];

      // Always move to the first point
      if (firstPoint) {
        CGContextMoveToPoint(context, point.x, point.y);
        firstPoint = FALSE;
        continue;
      }

      // Draw a point
      CGContextAddLineToPoint(context, point.x, point.y);
    }
  }

  // Stroke!
  CGContextStrokePath(context);
}

这里唯一的问题是setNeedsDisplay的表现不是很好。最好使用setNeedsDisplayInRect:,请参阅我上一篇关于an efficient way of determining the 'drawn' rect的帖子。

至于撤消?撤消操作只是弹出allPaths数组中的最后一个对象。这个练习我会告诉你:)

希望这有帮助!