thebookofshaders/glossary/atan/README.md

## Atan
Return the arc-tangent of the parameters

### Declaration
```glsl
float atan(float y, float x)  
vec2 atan(vec2 y, vec2 x)  
vec3 atan(vec3 y, vec3 x)  
vec4 atan(vec4 y, vec4 x)

float atan(float y_over_x)  
vec2 atan(vec2 y_over_x)  
vec3 atan(vec3 y_over_x)  
vec4 atan(vec4 y_over_x)
```

### Parameters
```y``` specify the numerator of the fraction whose arctangent to return.

```x``` specify the denominator of the fraction whose arctangent to return.

```y_over_x``` specify the fraction whose arctangent to return.

### Description
```atan()``` returns the angle whose trigonometric arctangent is ```y,x``` or ```y_over_x```, depending on which overload is invoked. In the first overload, the signs of ```y``` and ```x``` are used to determine the quadrant that the angle lies in. The values returned by atan in this case are in the range -PI and PI. Results are undefined if ```x``` is zero.

For the second overload, ```atan()``` returns the angle whose tangent is ```y_over_x```. Values returned in this case are in the range -PI to PI.

### See Also
[cos](/glossary/?search=cos), [acos](/glossary/?search=acos), [sin](/glossary/?search=sin), [asin](/glossary/?search=asin), [atan](/glossary/?search=atan), [Chapter 05: Shaping Functions](/05/), [Chapter 06: Color](/06/)