iPad（非常）简单的绘图

Question

我正在尝试在我的应用程序中实现一个非常简单的绘图视图。这只是我的应用程序的一小部分，但它正在变成一个真正的麻烦。这是我到目前为止所拥有的，但它现在显示的只是莫尔斯电码，如点和线。

  - (void)viewDidLoad {
        [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                         NSUserDomainMask, YES);
    NSString *docsPath = [paths objectAtIndex:0];

    NSString *savePath  = [NSString stringWithFormat:@"%@/notePadImage.jpg",docsPath];

    NSData *data = [NSData dataWithContentsOfFile:savePath];

    UIImage *image = [UIImage imageWithData:data];

    if (image == nil) {
        NSString *pathToBlank = [[NSBundle mainBundle]pathForResource:@"blankNotePadPage" ofType:@"png"];
        NSData *data = [NSData dataWithContentsOfFile:pathToBlank];
        image = [UIImage imageWithData:data];
    }
    arrayOfTouches = [[NSMutableArray alloc] initWithCapacity:10];
    self.drawImage.image = image;

    mouseMoved = 0;
    [self.view bringSubviewToFront:closeButton];
    [self.view bringSubviewToFront:clearButton];
    self.timer = [NSTimer scheduledTimerWithTimeInterval:.02 target:self selector:@selector(drawIt) userInfo:nil repeats:YES];

    }

    - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {


    UITouch *touch = [touches anyObject];

    [arrayOfTouches addObject:touch];




    }


    - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    [arrayOfTouches addObject:touch];


    }

    - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    }

    -(void) drawIt {

    NSMutableArray *tempArray = [NSMutableArray arrayWithArray:arrayOfTouches];
    [arrayOfTouches removeAllObjects];
    if ([tempArray count]>1) {

        [arrayOfTouches removeAllObjects];
        CGPoint point1 = [[tempArray objectAtIndex:0] previousLocationInView:self.view];;
        CGPoint point2;
        CGPoint point3;

        for (int i = 0; i < [tempArray count]-1;i = i+1) {




            UIGraphicsBeginImageContext(self.view.frame.size);
            [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
            CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
            CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 3.0);
            CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 0.0, 0.0, 1.0);
            CGContextMoveToPoint(UIGraphicsGetCurrentContext(), point1.x, point1.y);
            CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), point2.x, point2.y);

            CGContextStrokePath(UIGraphicsGetCurrentContext());
            CGContextFlush(UIGraphicsGetCurrentContext());
            drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            [self.view bringSubviewToFront:closeButton];
            [self.view bringSubviewToFront:clearButton];
            point1 = point2;

        }

        }   
    }

Answer 1

我的一个应用程序还需要一些简单的绘图。这是它的一个稍微修改的版本。它的工作原理基本上就像 hotpaw2 所描述的那样。我创建了一个“画布”视图来处理所有绘图，然后将其添加到需要的地方。

对于我的目的来说，速度很好。

CanvasView.h:

@interface CanvasView : UIView {
    NSMutableArray *points;
}
@property (nonatomic, retain) NSMutableArray *points;
@end

CanvasView.m:

#import "CanvasView.h"

@implementation CanvasView

@synthesize points;

- (id) initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        self.backgroundColor = [UIColor blueColor];
    }
    return self;
}

-(void)drawRect:(CGRect)rect
{
    if (self.points.count == 0)
        return;

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 1.0); //white
    CGContextSetLineWidth(context, 1.0);

    CGPoint firstPoint = [[self.points objectAtIndex:0] CGPointValue];
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, firstPoint.x, firstPoint.y);

    int i = 1;
    while (i < self.points.count)
    {
        CGPoint nextPoint = [[self.points objectAtIndex:i] CGPointValue];

        if (nextPoint.x < 0 && nextPoint.y < 0)
        {
            CGContextDrawPath(context, kCGPathStroke);

            if (i < (self.points.count-1))
            {
                CGContextBeginPath(context);
                CGPoint nextPoint2 = [[self.points objectAtIndex:i+1] CGPointValue];                
                CGContextMoveToPoint(context, nextPoint2.x, nextPoint2.y);
                i = i + 2;
            }
            else
                i++;
        }
        else
        {
            CGContextAddLineToPoint(context, nextPoint.x, nextPoint.y);
            i++;
        }
    }

    CGContextDrawPath(context, kCGPathStroke);
}

-(void)dealloc
{
    [points release];
    [super dealloc];
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event touchesForView:self] anyObject];
    CGPoint location = [touch locationInView:self];

    if (self.points == nil)
    {
        NSMutableArray *newPoints = [[NSMutableArray alloc] init];
        self.points = newPoints;
        [newPoints release];
    }

    [self.points addObject:[NSValue valueWithCGPoint:(location)]];
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event touchesForView:self] anyObject];
    CGPoint location = [touch locationInView:self];
    [self.points addObject:[NSValue valueWithCGPoint:(location)]];

    [self setNeedsDisplay];
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event touchesForView:self] anyObject];
    CGPoint location = [touch locationInView:self];
    [self.points addObject:[NSValue valueWithCGPoint:(location)]];

    CGPoint endPoint = CGPointMake(-99, -99); //"end of path" indicator
    [self.points addObject:[NSValue valueWithCGPoint:(endPoint)]];

    [self setNeedsDisplay];
}

@end

在需要的地方添加canvasView：

CanvasView *cv = [[CanvasView alloc] initWithFrame:CGRectMake(0, 0, 320, 640)];
[self.view addSubview:cv];
[cv release];

Answer 2

处理触摸时不要绘制。它会大大减慢触摸处理程序的速度，您可能会看到您所看到的连接点效果。

将触摸坐标保存在数组中并计划稍后绘制它们。

查看一些简单的动画教程，了解如何基于动画 UITimer 或 CADisplayLink 调用的 setNeedsDisplay 在 drawRect 中进行绘制。以更合适的速率绘制所有线段。