/*

     File: CrumbPathView.m 

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*/

#import "CrumbPathView.h"

#import "CrumbPath.h"

@interface CrumbPathView (FileInternal)

- (CGPathRef)newPathForPoints:(MKMapPoint *)points

                      pointCount:(NSUInteger)pointCount

                        clipRect:(MKMapRect)mapRect

                       zoomScale:(MKZoomScale)zoomScale;

@end

@implementation CrumbPathView

- (void)drawMapRect:(MKMapRect)mapRect

          zoomScale:(MKZoomScale)zoomScale

          inContext:(CGContextRef)context

{

    CrumbPath *crumbs = (CrumbPath *)(self.overlay);

    CGFloat lineWidth = MKRoadWidthAtZoomScale(zoomScale);

    // outset the map rect by the line width so that points just outside

    // of the currently drawn rect are included in the generated path.

    MKMapRect clipRect = MKMapRectInset(mapRect, -lineWidth, -lineWidth);

    [crumbs lockForReading];

    CGPathRef path = [self newPathForPoints:crumbs.points

                                    pointCount:crumbs.pointCount

                                      clipRect:clipRect

                                     zoomScale:zoomScale];

    [crumbs unlockForReading];

    if (path) {

        CGContextAddPath(context, path);

        CGContextSetRGBStrokeColor(context, 0, 0, 1.0, 0.5);

        CGContextSetLineJoin(context, kCGLineJoinRound);

        CGContextSetLineCap(context, kCGLineCapRound);

        CGContextSetLineWidth(context, lineWidth);

        CGContextStrokePath(context);

        CGPathRelease(path);

    }

}

@end

@implementation CrumbPathView (FileInternal)

static BOOL lineIntersectsRect(MKMapPoint p0, MKMapPoint p1, MKMapRect r) {

    double minX = MIN(p0.x, p1.x);

    double minY = MIN(p0.y, p1.y);

    double maxX = MAX(p0.x, p1.x);

    double maxY = MAX(p0.y, p1.y);

    MKMapRect r2 = MKMapRectMake(minX, minY, maxX - minX, maxY - minY);

    return MKMapRectIntersectsRect(r, r2);

}

#define MIN_POINT_DELTA 5.0

- (CGPathRef)newPathForPoints:(MKMapPoint *)points

                      pointCount:(NSUInteger)pointCount

                        clipRect:(MKMapRect)mapRect

                       zoomScale:(MKZoomScale)zoomScale

{

    // The fastest way to draw a path in an MKOverlayView is to simplify the

    // geometry for the screen by eliding points that are too close together

    // and to omit any line segments that do not intersect the clipping rect.  

    // While it is possible to just add all the points and let CoreGraphics 

    // handle clipping and flatness, it is much faster to do it yourself:

    if (pointCount < 2)

        return NULL;

    CGMutablePathRef path = NULL;

    BOOL needsMove = YES;

#define POW2(a) ((a) * (a))

    // Calculate the minimum distance between any two points by figuring out

    // how many map points correspond to MIN_POINT_DELTA of screen points

    // at the current zoomScale.

    double minPointDelta = MIN_POINT_DELTA / zoomScale;

    double c2 = POW2(minPointDelta);

    MKMapPoint point, lastPoint = points[0];

    NSUInteger i;

    for (i = 1; i < pointCount - 1; i++) {

        point = points[i];

        double a2b2 = POW2(point.x - lastPoint.x) + POW2(point.y - lastPoint.y);

        if (a2b2 >= c2) {

            if (lineIntersectsRect(point, lastPoint, mapRect)) {

                if (!path) 

                    path = CGPathCreateMutable();

                if (needsMove) {

                    CGPoint lastCGPoint = [self pointForMapPoint:lastPoint];

                    CGPathMoveToPoint(path, NULL, lastCGPoint.x, lastCGPoint.y);

                }

                CGPoint cgPoint = [self pointForMapPoint:point];

                CGPathAddLineToPoint(path, NULL, cgPoint.x, cgPoint.y);

            } else {

                // discontinuity, lift the pen

                needsMove = YES;

            }

            lastPoint = point;

        }

    }

#undef POW2

    // If the last line segment intersects the mapRect at all, add it unconditionally

    point = points[pointCount - 1];

    if (lineIntersectsRect(lastPoint, point, mapRect)) {

        if (!path)

            path = CGPathCreateMutable();

        if (needsMove) {

            CGPoint lastCGPoint = [self pointForMapPoint:lastPoint];

            CGPathMoveToPoint(path, NULL, lastCGPoint.x, lastCGPoint.y);

        }

        CGPoint cgPoint = [self pointForMapPoint:point];

        CGPathAddLineToPoint(path, NULL, cgPoint.x, cgPoint.y);

    }

    return path;

}

@end