OpenSpace/modules/space/shaders/debrisViz_fs.glsl

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2022                                                               *
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#include "fragment.glsl"

in vec4 viewSpacePosition;
in float viewSpaceDepth;
in float periodFraction;
in float offsetPeriods;

uniform vec3 color;
uniform float opacity = 1.0;
uniform float lineFade;


Fragment getFragment() {
  // float offsetPeriods = offset / period;
  // This is now done in the fragment shader instead to make smooth movement between
  // vertices. We want vertexDistance to be double up to this point, I think, (hence the
  // unnessesary float to float conversion)
  float vertexDistance = periodFraction - offsetPeriods;
  
  // This is the alternative way of calculating 
  // the offsetPeriods: (vertexID_perOrbit/nrOfSegments_f)
  // float vertexID_perOrbit = mod(vertexID_f, numberOfSegments);
  // float nrOfSegments_f = float(numberOfSegments);
  // float vertexDistance = periodFraction - (vertexID_perOrbit/nrOfSegments_f); 

  if (vertexDistance < 0.0) {
    vertexDistance += 1.0;
  }

  float invert = pow((1.0 - vertexDistance), lineFade);
  float fade = clamp(invert, 0.0, 1.0);

  // Currently even fully transparent lines can occlude other lines, thus we discard these
  // fragments since debris and satellites are rendered so close to each other
  if (fade < 0.05) {
    discard;
  }

  Fragment frag;
  if (fade < 0.15) {
    // Use additive blending for some values to make the discarding less abrupt
    frag.blend = BLEND_MODE_ADDITIVE;
  }

  frag.color = vec4(color, fade * opacity);
  frag.depth = viewSpaceDepth;
  frag.gPosition = viewSpacePosition;
  frag.gNormal = vec4(1.0, 1.0, 1.0, 0.0);

  return frag;
}