OpenSpace/modules/globebrowsing/shaders/rings_geom_fs.glsl

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2020                                                               *
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#include "PowerScaling/powerScaling_fs.hglsl"
#include "fragment.glsl"

in vec2 vs_st;
in float vs_screenSpaceDepth;

uniform sampler1D ringTexture;
uniform vec2 textureOffset;

Fragment getFragment() {
    // Moving the origin to the center
    vec2 st = (vs_st - vec2(0.5)) * 2.0;

    // The length of the texture coordinates vector is our distance from the center
    float radius = length(st);

    // We only want to consider ring-like objects so we need to discard everything else
    if (radius > 1.0) {
        discard;
    }

    // Remapping the texture coordinates
    // Radius \in [0,1],  texCoord \in [textureOffset.x, textureOffset.y]
    // textureOffset.x -> 0
    // textureOffset.y -> 1
    float texCoord = (radius - textureOffset.x) / (textureOffset.y - textureOffset.x);
    if (texCoord < 0.f || texCoord > 1.f) {
        discard;
    }

    float diffuse = length(texture(ringTexture, texCoord).rgb);
        
    // The normal for the one plane depends on whether we are dealing
    // with a front facing or back facing fragment
    //vec3 normal;
    // The plane is oriented on the xz plane
    // WARNING: This might not be the case for Uranus
    // if (gl_FrontFacing) {
    //     normal = vec3(-1.0, 0.0, 0.0);
    // }
    // else {
    //     normal = vec3(1.0, 0.0, 0.0);
    // }

    Fragment frag;
    frag.color      = vec4(vec3(vs_screenSpaceDepth), 1.0);
    frag.depth      = (diffuse < 0.5) ? 1E30 : vs_screenSpaceDepth;
    
    return frag;
}