使用CoreGraphics CGContextDrawImage在CATiledLayer中绘图

Question

我想在iPhone OS 3.1.3中使用CATiledLayer并且这样做所有绘图-(void)drawLayer:(CALayer *)layer inContext:(CGContext)context只需要使用coregraphics.

现在我遇到了iPhone上翻转坐标系的问题,并且有一些建议如何使用变换来修复它:

• 图像被颠倒了
• CATiledLayer或CALayer无法正常工作

我的问题是我无法让它发挥作用.我开始使用PhotoScroller示例代码并仅使用coregraphics调用替换绘图方法.看起来像这样

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context {
CGContextSaveGState(context);
CGRect rect = CGContextGetClipBoundingBox(context);
CGFloat scale = CGContextGetCTM(context).a;
CGContextConcatCTM(context, CGAffineTransformMakeTranslation(0.f, rect.size.height));
CGContextConcatCTM(context, CGAffineTransformMakeScale(1.f, -1.f));

CATiledLayer *tiledLayer = (CATiledLayer *)layer;
CGSize tileSize = tiledLayer.tileSize;


tileSize.width /= scale;
tileSize.height /= scale;
// calculate the rows and columns of tiles that intersect the rect we have been asked to draw
int firstCol = floorf(CGRectGetMinX(rect) / tileSize.width);
int lastCol = floorf((CGRectGetMaxX(rect)-1) / tileSize.width);
int firstRow = floorf(CGRectGetMinY(rect) / tileSize.height);
int lastRow = floorf((CGRectGetMaxY(rect)-1) / tileSize.height);
for (int row = firstRow; row <= lastRow; row++) {
    for (int col = firstCol; col <= lastCol; col++) {
     //   if (row == 0 ) continue;
        UIImage *tile = [self tileForScale:scale row:row col:col];
        CGImageRef tileRef = [tile CGImage];
        CGRect tileRect = CGRectMake(tileSize.width * col, tileSize.height * row,
                                     tileSize.width, tileSize.height);
        // if the tile would stick outside of our bounds, we need to truncate it so as to avoid
        // stretching out the partial tiles at the right and bottom edges
        tileRect = CGRectIntersection(self.bounds, tileRect);
        NSLog(@"row:%d, col:%d, x:%.0f y:%.0f, height:%.0f, width:%.0f", row, col,tileRect.origin.x, tileRect.origin.y, tileRect.size.height, tileRect.size.width);

        //[tile drawInRect:tileRect];
        CGContextDrawImage(context, tileRect, tileRef);
// just to draw the row and column index in the tile and mark the origin of the tile with a red line        
        if (self.annotates) {
            CGContextSetStrokeColorWithColor(context, [[UIColor whiteColor]CGColor]);
            CGContextSetLineWidth(context, 6.0 / scale);
            CGContextStrokeRect(context, tileRect);
            CGContextSetStrokeColorWithColor(context, [[UIColor redColor]CGColor]);
            CGContextMoveToPoint(context, tileRect.origin.x, tileRect.origin.y);
            CGContextAddLineToPoint(context, tileRect.origin.x+100.f, tileRect.origin.y+100.f);
            CGContextStrokePath(context);
            CGContextSetStrokeColorWithColor(context, [[UIColor redColor]CGColor]);
            CGContextSetFillColorWithColor(context, [[UIColor whiteColor]CGColor]);
            CGContextSelectFont(context, "Courier", 128, kCGEncodingMacRoman);
            CGContextSetTextDrawingMode(context, kCGTextFill);
            CGContextSetShouldAntialias(context, true);
            char text[30]; 
            int length = sprintf(text,"row:%d col:%d",row,col);
            CGContextSaveGState(context);
            CGContextShowTextAtPoint(context, tileRect.origin.x+110.f,tileRect.origin.y+100.f, text, length);
            CGContextRestoreGState(context);
        }
    }
}

CGContextRestoreGState(context);

}

如您所见,我使用"缩放"变换来反转坐标系,使用平移变换将原点移动到左下角.图像绘制正确但只绘制了第一行图块.我认为翻译操作或计算瓷砖坐标的方式存在问题.

这是它的样子:

我对所有这些转变感到困惑.

额外的问题:如何处理核心图形中的视网膜显示图片？

编辑: 为了让它在视网膜显示器上工作,我只是从示例代码中提取原始方法来提供图像:

- (UIImage *)tileForScale:(CGFloat)scale row:(int)row col:(int)col
{
// we use "imageWithContentsOfFile:" instead of "imageNamed:" here because we don't want UIImage to cache our tiles
NSString *tileName = [NSString stringWithFormat:@"%@_%d_%d_%d", imageName, (int)(scale * 1000), col, row];
NSString *path = [[NSBundle mainBundle] pathForResource:tileName ofType:@"png"];
UIImage *image = [UIImage imageWithContentsOfFile:path];
return image;
}

原则上,显示器的比例被忽略,因为Core Graphics以像素而不是点工作,因此当被要求绘制更多像素时,使用更多CATiledLayers(或子图层)来填充屏幕.

非常感谢托马斯

Answer 1

Thomas,我开始关注WWDC 2010 ScrollView演讲,很少或没有关于drawLayer:inContextiOS 3.x 内部工作的文档.我有同样的问题,你做的,当我从移动演示代码drawRect:对面drawLayer:inContext:.

一些调查显示,在返回 drawLayer:inContext:的大小和偏移范围内,正是您想要绘制的内容.在哪里给出了整个边界.rectCGContextGetClipBoundingBox(context)drawRect:

知道了这一点,您可以删除行和列迭代,以及边缘切片的CGRect交集,只需在翻译上下文后绘制到rect.

这就是我最终得到的结果:

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
  CGRect rect = CGContextGetClipBoundingBox(ctx);
  CGFloat scale = CGContextGetCTM(ctx).a;

  CATiledLayer *tiledLayer = (CATiledLayer *)[self layer];
  CGSize tileSize = tiledLayer.tileSize;
  tileSize.width /= scale;
  tileSize.height /= scale;

  int col = floorf((CGRectGetMaxX(rect)-1) / tileSize.width);
  int row = floorf((CGRectGetMaxY(rect)-1) / tileSize.height);

  CGImageRef image = [self imageForScale:scale row:row col:col];

  if(NULL != image) {
    CGContextTranslateCTM(ctx, 0.0, rect.size.height);
    CGContextScaleCTM(ctx, 1.0, -1.0);
    rect = CGContextGetClipBoundingBox(ctx);

    CGContextDrawImage(ctx, rect, image);
    CGImageRelease(image);
  }
}

请注意,rect在TranslateCTM和之后重新定义ScaleCTM.

以下是我的imageForScale:row:col功能:

- (CGImageRef) imageForScale:(CGFloat)scale row:(int)row col:(int)col {
  CGImageRef image = NULL;
  CGDataProviderRef provider = NULL;
  NSString *filename = [NSString stringWithFormat:@"img_name_here%0.0f_%d_%d",ceilf(scale * 100),col,row];
  NSString *path = [[NSBundle mainBundle] pathForResource:filename ofType:@"png"];

  if(path != nil) {
    NSURL *imageURL = [NSURL fileURLWithPath:path];

    provider = CGDataProviderCreateWithURL((CFURLRef)imageURL);

    image = CGImageCreateWithPNGDataProvider(provider,NULL,FALSE,kCGRenderingIntentDefault); 
    CFRelease(provider);
  }
  return image;
}

为了正确支持高分辨率图形,仍然需要对这两个功能进行一些工作,但除了iPhone 4之外,它确实看起来不错.