借鉴自定义MKOverlay

Question

我使用自定义MKOverlay通过MKMapView绘制天气数据.该图纸正在CoreGraphics中完成.对于这种特殊情况,仅仅在drawMapRect:zoomScale:inContext:方法中进行绘制是不够的,因为它处理平铺的方式.我需要立即绘制整个图像,而不是像drawMapRect方法那样平铺.

之前,我在.gif中有雷达图像所以我只是添加了一个imageView并在drawMapRect中调整了imageView框架的大小.

我的计划是做一些类似的事情.添加自定义UIView并在drawMapRect中调用setNeedsDisplay.

这是相关的代码.

MKOverlay对象的boundingMapRect属性:

- (MKMapRect)boundingMapRect
{
    CLLocationCoordinate2D upperLeftCoord = 
    CLLocationCoordinate2DMake(weatherData.radarArray.connectedRadar.latitude + 2.5,
                           weatherData.radarArray.connectedRadar.longitude - 2.5);

    MKMapPoint upperLeft = MKMapPointForCoordinate(upperLeftCoord);

    CLLocationCoordinate2D lowerRightCoord = 
    CLLocationCoordinate2DMake(weatherData.radarArray.connectedRadar.latitude - 2.5,
                           weatherData.radarArray.connectedRadar.longitude + 2.5);

    MKMapPoint lowerRight = MKMapPointForCoordinate(lowerRightCoord);

    double width = lowerRight.x - upperLeft.x;
    double height = lowerRight.y - upperLeft.y;

    MKMapRect bounds = MKMapRectMake(upperLeft.x, upperLeft.y, width, height);

    return bounds;
}

工作drawMapRect:zoomScale:inContext:代码(太慢了).

- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {

    int numPaths = parser.dataPaths.size();

    // We have to pad the map rect a lot to allow for visibility testing that works well.
    MKMapRect testMapRect = MKMapRectMake(mapRect.origin.x - 40000, mapRect.origin.y - 40000, mapRect.size.width + 40000, mapRect.size.height + 40000);;

    // Only draw inside the area we are suppose to
    //CGRect rect = [self rectForMapRect:mapRect];
    //CGContextClipToRect(context, rect);

    // How see through is the radar data. 1 = opaque, 0 = completely transparent
    CGContextSetAlpha(context, 1);
    for (int i = 0; i < numPaths; i++) {
        // Make sure the bin is actually visible in this region before drawing it
        if (MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[0]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[1]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[2]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[3])) {
            CGMutablePathRef path = CGPathCreateMutable();
            CGPoint currentP = [self pointForMapPoint:parser.dataPaths[i]->points[0]];
            CGContextBeginPath(context);
            CGPathMoveToPoint(path, NULL, currentP.x, currentP.y);
            currentP = [self pointForMapPoint:parser.dataPaths[i]->points[1]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);
            currentP = [self pointForMapPoint:parser.dataPaths[i]->points[2]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);
            currentP = [self pointForMapPoint:parser.dataPaths[i]->points[3]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);
            currentP = [self pointForMapPoint:parser.dataPaths[i]->points[0]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);
            CGPathCloseSubpath(path);
            CGContextSetFillColorWithColor(context, colors[parser.dataPaths[i]->dataVal]);
            CGContextAddPath(context, path);
            CGContextFillPath(context);
            CGPathRelease(path);
        }
}

新的drawMapRect:zoomScale:inContext:code

- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {

    // We have to pad the map rect a lot to allow for visibility testing that works well.
    radarImageView.testMapRect = MKMapRectMake(mapRect.origin.x - 40000, mapRect.origin.y - 40000, mapRect.size.width + 40000, mapRect.size.height + 40000);

    radarImageView.frame = [self rectForMapRect:self.overlay.boundingMapRect];
    [radarImageView setNeedsDisplay];

}

自定义UIView的drawRect方法.

- (void)drawRect:(CGRect)rect {


    CGContextRef context = UIGraphicsGetCurrentContext();

    int numPaths = parser.dataPaths.size();

    CGContextSetAlpha(context, 1);
    for (int i = 0; i < numPaths; i++) {

        // Make sure the bin is actually visible in this region before drawing it
        if (MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[0]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[1]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[2]) ||
            MKMapRectContainsPoint(testMapRect, parser.dataPaths[i]->points[3])) {

            CGMutablePathRef path = CGPathCreateMutable();
            CGPoint currentP = [(RadarImageOverlayView *)self.superview pointForMapPoint:parser.dataPaths[i]->points[0]];

            CGContextBeginPath(context);
            CGPathMoveToPoint(path, NULL, currentP.x, currentP.y);

            currentP = [(RadarImageOverlayView *)self.superview pointForMapPoint:parser.dataPaths[i]->points[1]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);

            currentP = [(RadarImageOverlayView *)self.superview pointForMapPoint:parser.dataPaths[i]->points[2]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);

            currentP = [(RadarImageOverlayView *)self.superview pointForMapPoint:parser.dataPaths[i]->points[3]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);

            currentP = [(RadarImageOverlayView *)self.superview pointForMapPoint:parser.dataPaths[i]->points[0]];
            CGPathAddLineToPoint(path, NULL, currentP.x, currentP.y);

            CGPathCloseSubpath(path);
            CGContextSetFillColorWithColor(context, colors[parser.dataPaths[i]->dataVal]);
            CGContextAddPath(context, path);
            CGContextFillPath(context);
            CGPathRelease(path);
        }
    }
}

谢谢!

编辑

我认为这个问题与RadarImageView的上下文有关.我在drawRect:方法中获取上下文的方式有问题吗？

Answer 1

你不能在调用drawMapRect之前准备好你的路径吗？例如当可见区域发生变化时。您只需将路径添加到drawMapRect中的绘图上下文中。我想您甚至可以准备给定比例的路径，然后在区域更改时平移和缩放上下文（CGContextScaleCTM）。

如果数据不经常改变。另一种优化是在获得数据后立即准备 png 格式的图像以实现较低的缩放级别。对于更高的缩放级别，您可以像以前一样继续绘制。

为了减少迭代次数，您可以对数据使用平铺：您可以为每个平铺使用一个数组，而不是使用一个包含所有数据的大数组。第一步，检索与当前可见区域相交的图块对应的数组，然后仅在这些数组上循环。当然，这只适用于更高的缩放级别。

如果不想优化，可以改善显示大量路径的情况下的用户体验。为了让用户在构建路径时与地图进行交互，您不应在一个循环中处理所有元素。您可以一次处理 1000 个路径，然后使用 PerformSelector:afterDelay: 延迟处理下一批。这样您就可以显示进度条并让用户与地图交互。