Angel between two lines wrong.

[amateur.jung8]

Hi.
I want to get angles between two line.
So I used this code.

------------------------------------
int posX = (ScreenWidth) >> 1;
int posY = (ScreenHeight) >> 1;
double radians, degrees;
radians = atan2f( y - posY , x - posX);
degrees = -CC_RADIANS_TO_DEGREES(radians);
NSLog(@"%f %f",degrees,radians);
-------------------------------------

But it doesn't work .
The Log is that: 146.309935 -2.553590

What's the matter?
I can't know the reason.
Please help me.

[GFish]

maybe your not getting it as your trying to work out the angel?! not the angle.... :P

[smithdale87]

Can you put in some sample data? What values do you use, what results do you get, and what are the correct results?

[CKAmike]

How do you know that is not the correct angle, it is less than 180 degrees and greater than 90, looks like it could be correct from the diagram you have drawn.

[Ridgewood]

Based on your drawing it looks like your code might just be off by 180 degrees. Try:

float pointAngle(float x1,float y1,float x2,float y2)
{
    float angle=atan2f(x2-x1,y2-y1);
    float degrees=angle*(180/M_PI);
    return 180.0f-degrees;
}

where x1 and y1 are your PosX and PosY and see if you like the results.

[amateur.jung8]

Originally Posted by smithdale87

Can you put in some sample data? What values do you use, what results do you get, and what are the correct results?

x,y position is touch position.
I've touched under the (posX,posY)
Also I've touched any position on the screen.
But the result is the same.
x: 146.309935
y: -2.553590

I can't know why it is.

[That Don Guy]

I think the problem is, you forgot that, on the screen, positive Y is down, not up, so in your picture, (Y - PosY) and (X - PosX) have different signs.

Based on this, atan2f should return the angle clockwise from the positive-X axis.

[amateur.jung8]

Thank for your help.
I solved this problem.
The reason is simple.
Here is a code I used.

if(x < posX )
{
radians = atan2( posX - x, y - posY);
degrees = 360 - CC_RADIANS_TO_DEGREES(radians);
}
else
{
radians = atan2( x - posX,y - posY);
degrees = CC_RADIANS_TO_DEGREES(radians);
}

And it works very well.
I've inserted wrong value to the x,y.
Sorry about this.

Best.