GLSL - void main(out vec4 O, vec2 U). Help?

Beginners
1

Hi Guys,

I’m slowly learning GLSL, I read both The Book of Shaders and Introduction to Touchdesigner especially the shading part. I started to convert some simple shaders found online and most of them with success. I’ve been stuck for a few hours now on this shader [url]https://www.shadertoy.com/view/XdlyzS[/url]

The shader looks like this:

float noise3( vec3 x , out vec2 g) {
    vec3 p = floor(x),f = fract(x),
        F = f*f*(3.-2.*f);   
#define hash3(p)  fract(sin(1e3*dot(p,vec3(1,57,-13.7)))*4375.5453)        
    
    float v000 = hash3(p+vec3(0,0,0)), v100 = hash3(p+vec3(1,0,0)),
          v010 = hash3(p+vec3(0,1,0)), v110 = hash3(p+vec3(1,1,0)),
          v001 = hash3(p+vec3(0,0,1)), v101 = hash3(p+vec3(1,0,1)),
          v011 = hash3(p+vec3(0,1,1)), v111 = hash3(p+vec3(1,1,1));
    
    g.x = 6.*f.x*(1.-f.x)                      
          * mix( mix( v100 - v000, v110 - v010, F.y),
                 mix( v101 - v001, v111 - v011, F.y), F.z);
    g.y = 6.*f.y*(1.-f.y)
          * mix( mix( v010 - v000, v110 - v100, F.x),
                 mix( v011 - v001, v111 - v101, F.x), F.z);
    
    return mix( mix(mix( v000, v100, F.x),      
                    mix( v010, v110, F.x),F.y),
                mix(mix( v001, v101, F.x),       
                    mix( v011, v111, F.x),F.y), F.z);
}


float noise(vec3 x, out vec2 g) {    
    vec2 g0,g1;
    float n = (noise3(x,g0)+noise3(x+11.5,g1)) / 2.;
    g = (g0+g1)/2.;
    return n;
}


void mainImage( out vec4 O, vec2 U ) 
{
    vec2 R = iResolution.xy;
    U *= 8./R.y;
    vec2 g;
    float n = noise(vec3(U,.1*iTime), g),
          v = sin(6.28*10.*n);
    //g = vec2(dFdx(n),dFdy(n));
    //O = vec4( sin(10.*atan(g.y,g.x)), v, 0,0); return; 
    g *= 6.28*10.*cos(6.28*10.*n) * 8./R.y;
  //v = tanh(2.*abs(v) / (abs(g.x)+abs(g.y))); 
    v = tanh(min(2.*abs(v) / (abs(g.x)+abs(g.y)),10.)); 
    n = floor(n*20.)/20.;
	O = v * (.5+.5*cos(12.*n+vec4(0,2.1,-2.1,0)));
}

I think I’m doing something wrong converting this specific part

void mainImage( out vec4 O, vec2 U )

After modifying the above to void main() I tried to insert at the top this:

layout (location=0) out vec4 O; out vec2 U;

and also this

layout (location=0) out vec4 O; layout (location=1)out vec2 U;

In both cases, the shader is compiled successfully but I only get a yellow/green still image.

What am I doing wrong? Any suggestion?

2

This modification will help

void main() // ------------ draw isovalues { vec2 R = iResolution.xy; vec2 U = gl_FragCoord.xy; // more code }
You’ll also replace iTime with iGlobalTime
And the final line will be

fragColor = v * (.5+.5*cos(12.*n+vec4(0,2.1,-2.1,0)));