我正在使用自定义MKOverlay在MKMapView上绘制天气数据。绘图是在CoreGraphics中完成的。对于这种特殊情况，仅凭其处理平铺的方式，不足以在drawMapRect:zoomScale:inContext:方法中进行绘制。我需要立即绘制整个图像，而不是像drawMapRect方法那样平铺。
以前，我将雷达图像保存为.gif格式，因此我只是向其中添加了一个imageView并在drawMapRect中调整了imageView框架的大小。
我的计划是对此做类似的事情。添加一个自定义UIView并在drawMapRect中对其调用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;
}
工作的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:代码
- (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
我认为问题与RadarImageView的上下文有关。我在drawRect:方法中获取上下文的方式是否有问题？
最佳答案
您不能在调用drawMapRect之前准备好路径。例如，当可见区域改变时。您只需要在drawMapRect中将路径添加到绘图上下文中即可，我想您甚至可以为给定比例准备路径，然后在区域更改时平移和缩放上下文(CGContextScaleCTM)。
如果数据不经常更改。另一种优化是在获取数据后立即为较低的缩放级别准备png格式的图像。对于更高的缩放级别，您可以继续进行绘制。
为了减少迭代次数，您可以对数据进行切片处理:您可以对每个切片使用一个数组，而不是对所有数据使用一个大数组。第一步，您检索与与当前可见区域相交的图块相对应的数组，然后仅在这些数组上循环。当然，这仅适用于更高的缩放级别。
如果您不想进行优化，则可以在显示大量路径的情况下改善用户体验。为了让用户在构建路径时与 map 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条路径，然后使用performSelector:afterDelay:延迟下一批的处理。这样，您可以显示进度条，并让用户与 map 进行交互。