Demo of shaders that can run anywhere

self-hosted-shadertoy.frag

void mainImage(out vec4 color,in vec2 fragCoord){
    vec2 resolution=iResolution.xy;
    // Adjusted coordinates to center the circle
    vec2 uv=(vec2(fragCoord.x,resolution.y-fragCoord.y)/resolution.xy-.5)*2.;
    float radius=iMouse.x/1000.;
    #ifdef PAPER_CRANES
        radius = energyNormalized;
    #endif
    // Calculate the distance from the center
    float dist=length(uv);

    // Determine if we're inside the circle
    if(dist<radius){
        // Inside the circle
        color=vec4(0.,0.,1.,1.);
        return;
    }
    color=vec4(0.,0.,0.,0.);// Transparent
}