🔮 Raymarching Distance Fields

Ray marching algorithm, used in combination with a special kind of function called SDF - signed distance functions, can create cool things in real time.

There aren’t using polygonal meshes and are instead using mathematical equations and the scene is drawn on a single quad that covers the camera’s field of vision.

The C code is boilerplate to run the OpenGL. The raymarching magic occurs in fragment shader wich determine the screen pixel colours.

🔵 Signed distance functions

SDF is a function that takes in a point as input and returns the shortest distance from that point to the surface any object in the scene. SDF additionally returns a negative number if the input point is inside of an object.

So our SDF, for a sphere centered at the origin with radius 1, looks like this:

f(x,y,z) = sqrt(x^2 + y^2 + z^2) - 1

f(1, 0, 0)   = 0      <- on the surface
f(0, 0, 0.5) = -0.5   <- inside
f(0, 3, 0)   = 2      <- outside

When we’re working in GLSL shader code, formulas like this will be vectorized:

  _      _
f(p) = ||p|| - 1

Which, in GLSL, translates to this:

float sphere_SDF(vec3 p)
{
	return length(p) - 1.0;
}

👉 More amazing SDFs you can find here

🔴 Raymarching

Raymarching is the alternative technique to Raytracing. Instead of casting out a ray and attempting to intersect a line with an object, raymarching marches along a ray based on the scene's SDF until the distance output from the function is < 0. We start at the camera, and move a point along the view ray, step by step. At each step, we check “Does the SDF evaluate to a negative number at this point?“. If it does, we’re hit something, else we keep going up to some maximum number of steps along the ray.

💡The lighting model used is the Blinn-Phong lighting model

Basics

• GCC
• OpenGL
• GLSL 3.3

Dependencies

• glew 2.1.0
• glfw 3.3.2

🟢 Run

git clone https://github.com/gitEllE-if/ray_marcher.git rayMarch

cd rayMarch

make

./RM

The program was tested and run on MacOS (Mojave, HighSierra, Catalina)

🟣 Shadertoy

Shadertoy is a tool that lets you experiment shaders without needing to write any OpenGL/WebGL boilerplate. You just write a fragment shader and watch how it work. It can be accessed here

🟡 Thanks

Thanks Inigo Quilez

He's great!