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Simplify shader and increase readability

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Emma Broman
2020-08-27 16:28:44 +02:00
parent 9e5251630a
commit 00814d07b1
1 changed files with 51 additions and 36 deletions
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modules/exoplanets/shaders/orbitdisc_fs.glsl
+51 -36
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@@ -34,56 +34,71 @@ uniform float opacity;
uniform float eccentricity;
uniform float semiMajorAxis;
const float AstronomicalUnit = 149597870700.0; // m
const float Epsilon = 0.0000001;
// Compute semi minor axis from major axis, a, and eccentricity, e
float semiMinorAxis(float a, float e) {
return a * sqrt(1.0 - pow(e, 2.0));
}
// If returned value <= 1, the point is insdie or on the ellipse specified by the input:
// a and b are the semi-major and semi-minor axes, respectively.
// cx is the displacement of the center of the ellipse along the x-axis (for an orbit,
// the y-displacement is always zero)
float ellipseTest(vec2 point, float a, float b, float cx) {
float x = point.x;
float y = point.y;
return (pow(x - cx, 2.0) / (a*a)) + ((y*y) / (b*b));
}
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 outer;
float inner;
float E = eccentricity;
float AU = semiMajorAxis;
float BU = AU * sqrt(1.0 - pow(E, 2.0)); // semi-minor axis
float CU = sqrt(pow(AU, 2.0) - pow(BU, 2.0));
float apo = AU * (1 + E);
float AUpper = semiMajorAxis;
float BUpper = semiMinorAxis(AUpper, eccentricity);
float CUpper = sqrt(AUpper*AUpper - BUpper*BUpper);
float outerApoapsisDistance = AUpper * (1 + eccentricity);
float AL = AU - textureOffset.x * 149597870700.0 - textureOffset.y * 149597870700.0;
float BL = AL * sqrt(1.0 - pow(E, 2.0));
float CL = sqrt(pow(AL, 2.0) - pow(BL, 2.0));
float apo_inner = AL * (1 + E);
float ALower = AUpper - AstronomicalUnit * (textureOffset.x + textureOffset.y);
float BLower = semiMinorAxis(ALower, eccentricity);
float CLower = sqrt(ALower*ALower - BLower*BLower);
float innerApoapsisDistance = ALower * (1 + eccentricity);
if(eccentricity <= 0.000000){
outer = pow(st.x, 2.0) / pow(AU/apo, 2.0) + ( pow(st.y, 2.0) / (pow(BU/apo, 2.0)));
inner = pow(st.x, 2.0) / pow(AL/apo, 2.0) + ( pow(st.y, 2.0) / (pow(BL/apo, 2.0)));
// Normalize based on outer apoapsis distance (size of plane)
float AU_n = AUpper / outerApoapsisDistance;
float BU_n = BUpper / outerApoapsisDistance;
float CU_n = CUpper / outerApoapsisDistance;
float AL_n = ALower / outerApoapsisDistance;
float BL_n = BLower / outerApoapsisDistance;
float CL_n = CLower / outerApoapsisDistance;
if (eccentricity <= Epsilon) {
CU_n = 0.0;
CL_n = 0.0;
}
else {
outer = pow((st.x + CU/apo), 2.0) / pow(AU/apo, 2.0) + pow(st.y, 2.0) / (pow(BU/apo, 2.0));
inner = pow((st.x + CL/apo), 2.0) / pow(AL/apo, 2.0) + pow(st.y, 2.0) / (pow(BL/apo, 2.0));
float outer = ellipseTest(st, AU_n, BU_n, -CU_n);
float inner = ellipseTest(st, AL_n, BL_n, -CL_n);
if (outer > 1.0 || inner < 1.0) {
// point is outside outer ellipse or inside inner eliipse
discard;
}
if (outer > 1.0) // point is outside outer ellipse
discard;
if (inner < 1.0) // point is inside inner ellipse
discard;
// Remapping the texture coordinates
vec2 dir = normalize(st);
// Find outer ellipse: where along the direction is the equation = 1
float scale;
if (eccentricity <= 0.000000) {
scale = sqrt((pow((AU/apo) * (BU/apo), 2)) / ((pow((BU/apo) * dir.x, 2)) + (pow((AU/apo) * dir.y, 2))));
}
else {
float first = -(pow(BU/apo, 2.0) * dir.x * (CU/apo)) / ( pow((BU/apo) * dir.x, 2.0) + pow((AU/apo) * dir.y, 2.0));
float second = pow((pow(BU/apo, 2.0) * dir.x * (CU/apo)) / (pow((BU/apo) * dir.x, 2.0) + pow((AU/apo) * dir.y, 2.0)), 2.0);
float third = (pow( (BU/apo) * (CU/apo) , 2.0) - pow((AU/apo) * (BU/apo), 2.0)) / (pow((BU/apo) * dir.x, 2.0) + pow((AU/apo) * dir.y, 2.0));
scale = first + sqrt(second - third);
}
// Find outer ellipse: where along the direction does the equation == 1?
float denominator = pow(BU_n * dir.x, 2.0) + pow(AU_n * dir.y, 2.0);
float first = -(pow(BU_n, 2.0) * dir.x * CU_n) / denominator;
float second = pow((pow(BU_n, 2.0) * dir.x * CU_n) / denominator, 2.0);
float third = (pow(BU_n * CU_n, 2.0) - pow(AU_n * BU_n, 2.0)) / denominator;
float scale = first + sqrt(second - third);
vec2 max = dir * scale;
vec2 min = max * (apo_inner/apo);
vec2 min = max * (innerApoapsisDistance / outerApoapsisDistance);
float distance1 = distance(max, min);
float distance2 = distance(max, st);