OpenSpace/modules/globebrowsing/shaders/rings_fs.glsl

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2025                                                               *
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#include "PowerScaling/powerScaling_fs.hglsl"
#include "fragment.glsl"
#include "ellipsoid.glsl"

#define NSSamplesMinusOne #{nShadowSamples}
#define NSSamples (NSSamplesMinusOne + 1)

in vec2 vs_st;
in float vs_screenSpaceDepth;
in vec4 shadowCoords;
in vec3 vs_normal;
in vec3 posObj;

uniform sampler1D ringTexture;
uniform vec2 textureOffset;
uniform float colorFilterValue;
uniform vec3 sunPosition;
uniform vec3 sunPositionObj;
uniform float nightFactor;
uniform float zFightingPercentage;
uniform float opacity;
uniform vec3 ellipsoidRadii;


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 < 0.0 || texCoord > 1.0) {
    discard;
  }

  vec4 diffuse = texture(ringTexture, texCoord);
  // divided by 3 as length of vec3(1.0, 1.0, 1.0) will return 3 and we want
  // to normalize the alpha value to [0,1]
  float colorValue = length(diffuse.rgb) / 3.0;
  if (colorValue < colorFilterValue) {
    diffuse.a = colorValue * colorFilterValue;
    if (diffuse.a < 0.65) {
      discard;
    }
}

  // Check if ray from fragment to sun intersects the ellipsoid (globe)
  // This creates more accurate shadowing for rings
  bool intersectsGlobe = rayIntersectsEllipsoid(
    posObj,
    sunPositionObj,
    vec3(0.0),
    ellipsoidRadii
  );

  // shadow == 1.0 means it is not in shadow
  float shadow = intersectsGlobe ? 0.05 : 1.0;

  // The normal for the one plane depends on whether we are dealing
  // with a front facing or back facing fragment
  // The plane is oriented on the xz plane
  // WARNING: This might not be the case for Uranus
  vec3 normal = gl_FrontFacing ? vec3(-1.0, 0.0, 0.0) : vec3(1.0, 0.0, 0.0);

  // Reduce the color of the fragment by the user factor
  // if we are facing away from the Sun
  if (dot(sunPosition, normal) < 0.0) {
    diffuse.xyz *= _nightFactor;
  }

  Fragment frag;

  frag.color = diffuse * shadow;
  frag.color.a *= opacity;
  frag.depth = vs_screenSpaceDepth;
  frag.gPosition = vec4(1e30, 1e30, 1e30, 1.0);
  frag.gNormal = vec4(normal, 1.0);

  return frag;
}