iphone - 绘制像素 - Objective-C/Cocoa

Question

我正在尝试在 xcode 中绘制单个像素以输出到 iphone。我不知道任何 OpenGL 或 Quartz 编码，但我对 Core Graphics 有一点了解。我正在考虑绘制宽度和高度为 1 的小矩形，但不知道如何在代码中实现它以及如何让它在视图中显示。任何帮助是极大的赞赏。

Answer 1

对于允许绘制固定大小和颜色的点的自定义 UIView 子类：

// Make a UIView subclass  
@interface PlotView : UIView  

@property (nonatomic) CGContextRef context;  
@property (nonatomic) CGLayerRef drawingLayer; // this is the drawing surface

- (void) plotPoint:(CGPoint) point; //public method for plotting  
- (void) clear; // erases drawing surface

@end  

// implementation  
#define kDrawingColor ([UIColor yellowColor].CGColor)
#define kLineWeight (1.5)

@implementation PlotView  
@synthesize context = _context, drawingLayer = _drawingLayer;

- (id) initPlotViewWithFrame:(CGRect) frame; {  

    self = [super initWithFrame:frame];
    if (self) {
        // this is total boilerplate, it rarely needs to change
        self.backgroundColor = [UIColor clearColor];
        CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
        CGFloat width = frame.size.width;
        CGFloat height = frame.size.height;
        size_t bitsPerComponent = 8;
        size_t bytesPerRow = (4 * width);
        self.context = CGBitmapContextCreate(NULL, width, height, bitsPerComponent, bytesPerRow, colorspace, kCGImageAlphaPremultipliedFirst);
        CGColorSpaceRelease(colorspace);
        CGSize size = frame.size;
        self.drawingLayer = CGLayerCreateWithContext(self.context, size, NULL);
    }
    return self;  
}  

// override drawRect to put drawing surface onto screen
// you don't actually call this directly, the system will call it
- (void) drawRect:(CGRect) rect; {

    // this creates a new blank image, then gets the surface you've drawn on, and stamps it down
    // at some point, the hardware will render this onto the screen
    CGContextRef currentContext = UIGraphicsGetCurrentContext();
    CGImageRef image = CGBitmapContextCreateImage(self.context);
    CGRect bounds = [self bounds];
    CGContextDrawImage(currentContext, bounds, image);
    CGImageRelease(image);
    CGContextDrawLayerInRect(currentContext, bounds, self.drawingLayer);
}

// simulate plotting dots by drawing a very short line with rounded ends
// if you need to draw some other kind of shape, study this part, along with the docs
- (void) plotPoint:(CGPoint) point; {

    CGContextRef layerContext = CGLayerGetContext(self.drawingLayer); // get ready to draw on your drawing surface

    // prepare to draw
    CGContextSetLineWidth(layerContext, kLineWeight);
    CGContextSetLineCap(layerContext, kCGLineCapRound);
    CGContextSetStrokeColorWithColor(layerContext, kDrawingColor);

    // draw onto surface by building a path, then stroking it
    CGContextBeginPath(layerContext); // start

    CGFloat x = point.x;
    CGFloat y = point.y;
    CGContextMoveToPoint(layerContext, x, y);
    CGContextAddLineToPoint(layerContext, x, y);

    CGContextStrokePath(layerContext); // finish

    [self setNeedsDisplay]; // this tells system to call drawRect at a time of it's choosing
}

- (void) clear; {

CGContextClearRect(CGLayerGetContext(self.drawingLayer), [self bounds]);
[self setNeedsDisplay];
}

// teardown
- (void) dealloc; {  

    CGContextRelease(_context);  
    CGLayerRelease(_drawingLayer);  
    [super dealloc];
}

Answer 2

如果您希望能够绘制累积添加到某些先前绘制的像素的像素，那么您将需要创建自己的位图图形上下文，并由您自己的位图内存支持。然后，您可以在位图内存中设置单个像素，或在图形上下文中绘制短线或小矩形。要显示您的绘图上下文，首先将其转换为 CGImageRef。然后，您可以将此图像绘制到视图的 drawRect 中的子类 UIView，或者将图像分配给 UIView 的 CALayer 的内容。

在 Apple 的文档中查找：CGBitmapContextCreate 和 CGBitmapContextCreateImage。

添加：

我在我的博客上写了一个更长的解释，解释为什么在 iOS 应用程序中绘制像素时可能需要这样做，以及一些源代码片段：http: //www.musingpaw.com/2012/04/drawing-in- ios-apps.html

Answer 3

所有绘图都需要进入该 - (void)drawRect:(CGRect)rect方法。[self setNeedsDisplay]标记代码以进行重绘。问题是你什么都没有重绘。