Fragment shader - sphere ray tracing - nothing displayed

Question

I'd like to do a simple raytracer to display a shaded sphere using the fragment shader.

I did the current code to at least display a circle, but this does not display anything. I assume the maths to be correct since it is a simple quadratic formula :

struct Sphere
{
    vec3 center;
    float radius;
};

struct Light
{
    vec3 pos;
    vec3 color;
    float intensity;
};

struct Ray
{
    vec3 orig;
    vec3 dir;
};


bool quadratic(float a, float b, float c, out float s1, out float s2)
{
    float delta = (b*b) - (4.0*a*c);
    if(delta < 0.0)
    {
        return false;

    }
    if(delta == 0.0)
    {
        s1 = s2 = (-b / (2.0*a));
        return true;
    }
    else
    {
        s1 = (-b-sqrt(delta))/(2.0*a);
        s2 = (-b+sqrt(delta))/(2.0*a);
        return true;
    }
}

bool iSphere(Ray r, Sphere s, out float t)
{
    vec3  l = r.orig - s.center;
    float a = dot(r.dir, r.dir);
    float b = 2.0*dot(r.dir,l);
    float c = dot(l,l) - (s.radius*s.radius);

    float s1, s2;
    if(quadratic(a,b,c,s1,s2) == true)
    {
        t = min(s1,s2);
        return true;
    }

    return false;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord.xy / iResolution.xy;

    /////////////////////////////////////////
    /////////DECLARE SCENE///////////////////
    /////////////////////////////////////////
    Sphere s;
    s.center = vec3(0.0, 0.0, -3.0);
    s.radius = 1.0;

    Light l;
    l.pos = vec3(0.0, 5.0, -3.0);
    l.color = vec3(1.0, 1.0, 1.0);
    l.intensity = 2.0;

    /////////////////////////////////////////
    ////////////CAST THE RAY/////////////////
    /////////////////////////////////////////
    Ray r;
    r.orig = vec3(0.0, 2.0, -3.0);
    r.dir = vec3(-1.0+2.0*uv, -1.0);

    /////////////////////////////////////////
    ////////////COMPUTE INTERSECTION/////////
    /////////////////////////////////////////
    float t;
    if(iSphere(r,s,t) == true)
    {
        fragColor = vec4(1,0,0,1);
    }
    else
    {
        fragColor = vec4(1,1,0,1);
    }    
}

I'm having a hard time to get why this is not working...

Any ideas ?

nabr nabr · Accepted Answer · 2017-02-23T05:22:55

this is not an good answer :)

your intersection test is valid I have changed the origin from negative to positive and i can see a sphere

r.orig = vec3(0.0, 2.0, 3.0);

P=o + t*dir

Im also learning raytracing. if you don't mind to share your shadertoy account. You leave a comment, something like that. I can follow your progression, and we learn together.

here is the shadertoy (i did some code clean up, we are a good team)

Fragment shader - sphere ray tracing - nothing displayed

1 Answers