CODEWITHSUNDEEP
iosiphonecocoacgpath
ios Dev
ios Dev

Reputation: 68

Draw a line to the given point and degrees on a view in ios?

i have a situation where the user will tap on the screen and enters the degrees and a line should to be draw from the tapped point in the given degree.

i am using the following path code to draw the line but i am not able to draw the line in the correct degree.

 CGMutablePathRef path = CGPathCreateMutable();
 CGPathMoveToPoint(path,NULL,touchx,touchy);
 CGPathAddLineToPoint(path, NULL,endX, endY);
 lineLayer = [CAShapeLayer layer];
 [lineLayer setPath:path];
 [lineLayer setFillColor:[[UIColor lightTextColor] CGColor]];
 [lineLayer setStrokeColor:[[UIColor blackColor] CGColor]];
 [lineLayer setAnchorPoint:CGPointMake(0.0f, 0.0f)];
 [lineLayer setPosition:CGPointMake(0.0f, 0.0f)];
 [drawingview.layer addSublayer:lineLayer];
 CGPathRelease(path);

Upvotes: 0

Views: 927

Answers (1)

Duncan C
Duncan C

Reputation: 131503

You posted code that creates a path with a start point, and and end point, but did not post the most important bit: how you calculate the end point.

I assume that's the part you need help with.

You need to use basic trigonometry. Trig on iOS is based on radians, so you will need to convert degrees to radians:

CGFloat radians = M_PI * degrees / 180.0;

Then you need to calculate your end point based on your start point.

Remember the mnemonic of the Indian chief "SOH CAH TOA" (sine = opposite/hypotenuse, cosine = adjacent/hypotenuse, tangent = opposite/adjacent).

Drawing a diagram of a right triangle with the angle in question on the left and the right angle on the right:

enter image description here

The X measurement is the adjacent side.

So, if cosine = adjacent/hypotenuse, then adjacent = cos * hypotenuse.

The hypotenuse of the triangle is the radius of the circle. Replacing variables:

x = cos(angle) * radius

The y measurement is the opposite side.

If sine = opposite/hypotenuse, then opposite = sine * hypotenuse.

The hypotenuse of the triangle is the radius of the circle. Replacing variables:

y = sin(angle) * radius

So your code to calculate the end-point might look like this:

CGFloat radius = 50; //Picked out of thin air; decide on a radius value

CGFloat deltaX = radius * cosf(radians);
CGFloat deltaY = radius * sinf(radians);

endX = touchX+deltaX;
endy = touchY+deltaY;

Upvotes: 2

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