138 lines
3.0 KiB
GLSL
138 lines
3.0 KiB
GLSL
uniform vec3 uSunPos = vec3( 0, 0.1, -1 );
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in vec3 v_direction;
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out vec4 fragcolor;
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vec3 atmosphere(vec3 r, vec3 r0, vec3 pSun, float iSun, float rPlanet, float rAtmos, vec3 kRlh, float kMie, float shRlh, float shMie, float g);
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void main() {
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vec3 color = atmosphere(
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normalize(v_direction),
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vec3(0,6372e3,0),
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uSunPos,
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22.0,
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6371e3,
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6471e3,
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vec3(5.5e-6, 13.0e-6, 22.4e-6),
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21e-6,
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8e3,
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1.2e3,
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0.758
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);
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color = 1.0 - exp(-1.0 * color);
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fragcolor = vec4(color, 1);
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}
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#define PI 3.141592
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#define iSteps 16
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#define jSteps 8
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vec2 rsi(vec3 r0, vec3 rd, float sr) {
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float a = dot(rd, rd);
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float b = 2.0 * dot(rd, r0);
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float c = dot(r0, r0) - (sr * sr);
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float d = (b*b) - 4.0*a*c;
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if (d < 0.0) return vec2(1e5,-1e5);
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return vec2(
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(-b - sqrt(d))/(2.0*a),
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(-b + sqrt(d))/(2.0*a)
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);
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}
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vec3 atmosphere(vec3 r, vec3 r0, vec3 pSun, float iSun, float rPlanet, float rAtmos, vec3 kRlh, float kMie, float shRlh, float shMie, float g) {
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pSun = normalize(pSun);
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r = normalize(r);
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vec2 p = rsi(r0, r, rAtmos);
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if (p.x > p.y) return vec3(0,0,0);
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p.y = min(p.y, rsi(r0, r, rPlanet).x);
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float iStepSize = (p.y - p.x) / float(iSteps);
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float iTime = 0.0;
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vec3 totalRlh = vec3(0,0,0);
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vec3 totalMie = vec3(0,0,0);
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float iOdRlh = 0.0;
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float iOdMie = 0.0;
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float mu = dot(r, pSun);
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float mumu = mu * mu;
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float gg = g * g;
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float pRlh = 3.0 / (16.0 * PI) * (1.0 + mumu);
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float pMie = 3.0 / (8.0 * PI) * ((1.0 - gg) * (mumu + 1.0)) / (pow(1.0 + gg - 2.0 * mu * g, 1.5) * (2.0 + gg));
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for (int i = 0; i < iSteps; i++) {
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vec3 iPos = r0 + r * (iTime + iStepSize * 0.5);
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float iHeight = length(iPos) - rPlanet;
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float odStepRlh = exp(-iHeight / shRlh) * iStepSize;
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float odStepMie = exp(-iHeight / shMie) * iStepSize;
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iOdRlh += odStepRlh;
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iOdMie += odStepMie;
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float jStepSize = rsi(iPos, pSun, rAtmos).y / float(jSteps);
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float jTime = 0.0;
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float jOdRlh = 0.0;
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float jOdMie = 0.0;
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for (int j = 0; j < jSteps; j++) {
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vec3 jPos = iPos + pSun * (jTime + jStepSize * 0.5);
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float jHeight = length(jPos) - rPlanet;
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jOdRlh += exp(-jHeight / shRlh) * jStepSize;
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jOdMie += exp(-jHeight / shMie) * jStepSize;
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jTime += jStepSize;
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}
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vec3 attn = exp(-(kMie * (iOdMie + jOdMie) + kRlh * (iOdRlh + jOdRlh)));
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totalRlh += odStepRlh * attn;
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totalMie += odStepMie * attn;
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iTime += iStepSize;
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}
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return iSun * (pRlh * kRlh * totalRlh + pMie * kMie * totalMie);
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} |