GLSL tips and snippets

Here are some of my favorite copy-pasta recipes:

Angles

Find angle of point relative to (0,0):

float angle = atan(pos.y, pos.x);

To rotate the scene around (0,0):

float a = 0.2; // your angle
pos *= mat2(cos(a), -sin(a), sin(a), cos(a));

Put these at the top of your file.

Define PI for future use:

#define PI 3.14159265359

And why not PI2:

#define PI2 6.28318530718

To get the polar coordinates of a point:

#define ANGLE(p) atan(p.y, p.x)
#define POLAR(p) vec2(ANGLE(p), length(p));
#define INV_POLAR(c) vec2(c.y * cos(c.x), c.y * sin(c.x));

Usage example:

vec2 c = POLAR(p);

c.y += 0.1 * cos(c.x * 20.0);

p = INV_POLAR(c);