simple sphere

/*
=================================================
BLOKS Shader Header v1.0
=================================================

@title       Blue SDF Sphere
@author      BLOKS
@description Minimal raymarched sphere with mouse-controlled camera orbit, soft blue lighting, fresnel glow, and subtle vignette.

@category    Raymarching
@tags        sdf, sphere, raymarching, mouse, camera, blue, fresnel, minimal

@audio       false
@mouse       true
@featured    false

@version     1.0.0
@license     BLOKS
*/

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

float map(vec3 p)
{
    return sdSphere(p, 1.0);
}

mat2 rot(float a)
{
    float c = cos(a);
    float s = sin(a);

    return mat2(c, -s, s, c);
}

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)
    ));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec2 p = uv * 2.0 - 1.0;
    p.x *= iResolution.x / iResolution.y;

    /*
    -------------------------------------------------
    Pointer / mouse
    -------------------------------------------------
    uPointer is normalized 0..1.
    This replaces older iMouse.xy behavior.
    -------------------------------------------------
    */

    vec2 m = uPointer;

    float yaw = (m.x - 0.5) * 1.8;
    float pitch = (m.y - 0.5) * 1.1;

    /*
    -------------------------------------------------
    Ray setup
    -------------------------------------------------
    */

    vec3 ro = vec3(0.0, 0.0, -4.0);
    vec3 rd = normalize(vec3(p, 1.5));

    rd.xz *= rot(yaw);
    rd.yz *= rot(pitch);

    /*
    -------------------------------------------------
    Raymarch
    -------------------------------------------------
    */

    float t = 0.0;
    float hit = 0.0;

    for (int i = 0; i < 80; i++)
    {
        vec3 pos = ro + rd * t;
        float d = map(pos);

        if (d < 0.001)
        {
            hit = 1.0;
            break;
        }

        t += d;

        if (t > 20.0)
        {
            break;
        }
    }

    /*
    -------------------------------------------------
    Shading
    -------------------------------------------------
    */

    vec3 bg = vec3(0.02, 0.03, 0.08);
    vec3 col = bg;

    if (hit > 0.5)
    {
        vec3 pos = ro + rd * t;
        vec3 normal = getNormal(pos);

        vec3 lightDir = normalize(vec3(0.6, 0.8, -0.5));
        float diff = max(dot(normal, lightDir), 0.0);

        float fresnel = pow(1.0 - max(dot(normal, -rd), 0.0), 3.0);

        vec3 base = vec3(0.10, 0.20, 0.85);
        vec3 glow = vec3(0.25, 0.65, 1.0);

        col = base * (0.18 + diff * 0.85);
        col += glow * fresnel * 0.75;
    }

    /*
    -------------------------------------------------
    Vignette
    -------------------------------------------------
    */

    float vignette = smoothstep(1.4, 0.2, length(p));
    col *= vignette;

    fragColor = vec4(col, 1.0);
}