Introduction to Raymarching

Introduction

Raymarching is one of the most fascinating techniques in modern shader programming.

It allows developers and artists to create fake 3D scenes, surreal environments, fractals, tunnels, abstract geometry, and cinematic visuals — all inside a fragment shader.

This is one of the reasons raymarching became so popular in the demoscene, generative art, Shadertoy, live visuals, and experimental GLSL projects.

What Is Raymarching?

Raymarching is a rendering technique where rays are stepped forward through a scene until they hit a surface.

Instead of rendering polygons, the shader mathematically describes objects.

The ray advances by that distance, then repeats the process until a surface is reached or the ray exits the scene.

How Traditional 3D Rendering Works

Most traditional 3D graphics use vertices, polygons, meshes, and rasterization.

Objects are built from triangles.

Signed Distance Fields (SDFs)

Most raymarching systems rely on Signed Distance Fields, often called SDFs.

An SDF is a mathematical function that returns the distance from a point to a surface.

Simple Sphere SDF

A sphere can be described mathematically using a very small amount of code.

float sdSphere(vec3 p, float r)
{
    return length(p) - r;
}

This function returns the distance to the sphere surface.

The Raymarching Process

Raymarching typically works through iterative stepping.

Step 1
Create a ray from the camera.

↓

Step 2
Sample the scene distance.

↓

Step 3
Move forward by that distance.

↓

Step 4
Repeat until hit
or maximum distance reached.

This process repeats continuously for every visible pixel.

Basic Raymarch Loop

Here is the core structure used in many raymarching shaders.

float d = 0.0;

for(int i = 0; i < 100; i++)
{
    vec3 p = ro + rd * d;

    float ds = map(p);

    d += ds;

    if(ds < 0.001) break;
}

The ray advances through the scene until it reaches a surface or exits the world.

Camera Rays

Every pixel shoots a ray into the scene.

The camera usually consists of a ray origin and a ray direction.

vec3 ro = vec3(0.0, 0.0, -5.0);
vec3 rd = normalize(vec3(uv, 1.0));

• ro = ray origin
• rd = ray direction

Combining Shapes

SDFs can be combined mathematically to build more complex scenes.

float scene(vec3 p)
{
    float sphere = sdSphere(p, 1.0);

    return sphere;
}

More advanced scenes combine spheres, boxes, cylinders, toruses, and procedural structures.

Smooth Blending

One of the coolest raymarching features is smooth unions.

Objects can melt together organically.

float smoothMin(float a, float b, float k)
{
    float h = max(k - abs(a - b), 0.0) / k;

    return min(a, b)
        - h * h * h * k * (1.0 / 6.0);
}

This creates liquid blending, organic surfaces, and surreal forms.

Surface Normals

Lighting requires surface normals.

Normals are estimated using nearby distance samples.

vec3 getNormal(vec3 p)
{
    vec2 e = vec2(0.001, 0.0);

    return normalize(vec3(
        map(p + e.xyy) - map(p - e.xyy),
        map(p + e.yxy) - map(p - e.yxy),
        map(p + e.yyx) - map(p - e.yyx)
    ));
}

This approximates surface direction for lighting calculations.

Lighting in Raymarching

Once a surface is hit, lighting, shadows, reflections, and glow can be added.

float diff = max(dot(normal, lightDir), 0.0);

This creates directional diffuse lighting.

Raymarched Shadows

Shadows are often created by casting secondary rays toward light sources.

This creates soft shadows, ambient occlusion, and cinematic depth.

Raymarching and Fractals

Raymarching is extremely popular for fractals because geometry is mathematical and recursion becomes possible.

This allows impossible structures and infinite procedural forms to emerge.

Why Raymarching Looks So Unique

Raymarching naturally creates smooth surfaces, surreal geometry, volumetric depth, atmospheric lighting, and dreamlike spaces.

Performance Considerations

Raymarching can become extremely expensive because every pixel may require dozens or hundreds of scene evaluations.

Raymarching in Audio Reactive Visuals

Raymarching works beautifully with audio reactivity.

Music can influence geometry, distortion, camera movement, glow, and scene evolution.

This creates immersive music tunnels, psychedelic environments, and evolving visual worlds.

Raymarching on the Web

WebGL made raymarching widely accessible through platforms like Shadertoy, Synesthesia, and browser-based GLSL systems.

This helped popularize procedural art, shader experimentation, and interactive graphics directly inside the browser.

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