example. ray marching (naïve) [ag-0019]

✍️source

/* The SDF for a sphere with radius r */
float sdSphere(vec3 p, float r)
{
  return length(p) - r;
}

/* The SDF for a scene with a unit sphere at the origin */
float sdScene(in vec3 pos) {
    return sdSphere(pos, 1.0);
}

#define EPSILON 0.01
#define T_MAX 10.0
#define DELTA_T 0.1
#define SDF_FUNCTION sdScene

/* Ray marching (naïve) */
float rayMarch(in vec3 ro, in vec3 rd) {

    float t = 0.0;

    while(t < T_MAX) {
        vec3 rt = ro + t * rd;
        float ft = SDF_FUNCTION(rt);
        
        if(ft < EPSILON) return t;

        t += DELTA_T;
    }
    
    return T_MAX;
}

/* The main function to render the scene per pixel */
void mainImage(out vec4 pixelColor, in vec2 pixelCoordinate) {
    
    // set up uv coordinates on the screen
    float aspect = iResolution.x/iResolution.y;
    vec2 uv = pixelCoordinate/iResolution.xy;
    uv -= vec2(0.5, 0.5);
    uv *= 2.0 * vec2(aspect, 1.0);

    // set up camera and view ray
    float observerDistance = 8.0;
    vec3 ro = vec3(0.0, 0.0, observerDistance);
    vec3 ta = ro - vec3(uv, 5.0);
    vec3 rd = normalize(ta - ro);

    // ray march
    float t = rayMarch(ro, rd);
    float hit = t != T_MAX ? 1.0 : 0.0;

    // adjust the color to look just bright enough
    float baseRatio = 0.65;
    // the closer, the brighter
    float distRatio = baseRatio + smoothstep(0.0, 1.0 - baseRatio, 1.0 - t / observerDistance);
    vec3 col = distRatio * vec3(1.0);

    // transparent if not hit
    pixelColor = vec4(col, hit);
}