CODEWITHSUNDEEP
objective-cioscocoa-touchcore-graphics
ozba
ozba

Reputation: 6643

How to find an arrow tip points given origin and end point of a line

Consider you have a line with start point (x1,y1) and end point (x2,y2).

In order to draw an arrow cap to the line (in objective-c), I need to find the points of the arrow (x3,y3,x4,y4) given the angle of the arrow (45 degrees), and the length of the arrow tips (h).

So given x1,y1,x2,y2,h,alpha whats x3,y3,x4,y4?

Added an image explaining the question.

If the answer can be in objective-c (using UIBezierpath and CGPoint) it will be much appreciated.

Thanks!arrow drawing

Upvotes: 3

Views: 1175

Answers (2)

emre
emre

Reputation: 73

This is my java implementation for my needs. start and end are Point objects.

    double lineAngle = Math.atan2(end.y-start.y, start.x-end.x);
    double ang1 = lineAngle-Math.PI/6;
    double ang2 = lineAngle+Math.PI/6;
    
    int tipLen = 30;
    Point tip1 = new Point(end.x+(int)(tipLen*Math.cos(ang1)), end.y-(int)(tipLen*Math.sin(ang1)));
    Point tip2 = new Point(end.x+(int)(tipLen*Math.cos(ang2)), end.y-(int)(tipLen*Math.sin(ang2)));
    
    g.drawLine(end.x,end.y,tip1.x,tip1.y);
    g.drawLine(end.x,end.y,tip2.x,tip2.y);

Calculate the angle of the tips and find their positions using angles.

Upvotes: 0

user529758
user529758

Reputation: 

#import <math.h>
#import <UIKit/UIKit.h>
#import <CoreGraphics/CoreGraphics.h>

float phi = atan2(y2 - y1, x2 - x1); // substitute x1, x2, y1, y2 as needed
float tip1angle = phi - M_PI / 4; // -45°
float tip2angle = phi + M_PI / 4; // +45°

float x3 = x2 - h * cos(tip1angle); // substitute h here and for the following 3 places
float x4 = x2 - h * cos(tip2angle);
float y3 = y2 -  h * sin(tip1angle);
float y4 = y2 -  h * sin(tip2angle);

CGPoint arrowStartPoint = CGPointMake(x1, y1);
CGPoint arrowEndPoint = CGPointMake(x2, y2);
CGPoint arrowTip1EndPoint = CGPointMake(x3, y3);
CGPoint arrowTip2EndPoint = CGPointMake(x4, y4);

CGContextRef ctx = UIGraphicsGetCurrentContext(); // assuming an UIView subclass
[[UIColor redColor] set];
CGContextMoveToPoint(ctx, arrowStartPoint.x, arrowStartPoint.y);
CGContextAddLineToPoint(ctx, arrowEndPoint.x, arrowEndPoint.y);
CGContextAddLineToPoint(ctx, arrowTip1EndPoint.x, arrowTip1EndPoint.y);
CGContextMoveToPoint(ctx, arrowEndPoint.x, arrowEndPoint.y);
CGContextAddLineToPoint(ctx, arrowTip2EndPoint.x, arrowTip2EndPoint.y);

I hope this helps :)

Upvotes: 8

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