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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 | //This file is automatically rebuilt by the Cesium build process.
export default "/**\n\
* This function computes the colors contributed by Rayliegh and Mie scattering on a given ray, as well as\n\
* the transmittance value for the ray. This function uses automatic uniforms\n\
* so the atmosphere settings are always synced with the current scene.\n\
*\n\
* @name czm_computeScattering\n\
* @glslfunction\n\
*\n\
* @param {czm_ray} primaryRay The ray from the camera to the position.\n\
* @param {float} primaryRayLength The length of the primary ray.\n\
* @param {vec3} lightDirection The direction of the light to calculate the scattering from.\n\
* @param {vec3} rayleighColor The variable the Rayleigh scattering will be written to.\n\
* @param {vec3} mieColor The variable the Mie scattering will be written to.\n\
* @param {float} opacity The variable the transmittance will be written to.\n\
*/\n\
void czm_computeScattering(\n\
czm_ray primaryRay,\n\
float primaryRayLength,\n\
vec3 lightDirection,\n\
float atmosphereInnerRadius,\n\
out vec3 rayleighColor,\n\
out vec3 mieColor,\n\
out float opacity\n\
) {\n\
const float ATMOSPHERE_THICKNESS = 111e3; // The thickness of the atmosphere in meters.\n\
const int PRIMARY_STEPS_MAX = 16; // Maximum number of times the ray from the camera to the world position (primary ray) is sampled.\n\
const int LIGHT_STEPS_MAX = 4; // Maximum number of times the light is sampled from the light source's intersection with the atmosphere to a sample position on the primary ray.\n\
\n\
// Initialize the default scattering amounts to 0.\n\
rayleighColor = vec3(0.0);\n\
mieColor = vec3(0.0);\n\
opacity = 0.0;\n\
\n\
float atmosphereOuterRadius = atmosphereInnerRadius + ATMOSPHERE_THICKNESS;\n\
\n\
vec3 origin = vec3(0.0);\n\
\n\
// Calculate intersection from the camera to the outer ring of the atmosphere.\n\
czm_raySegment primaryRayAtmosphereIntersect = czm_raySphereIntersectionInterval(primaryRay, origin, atmosphereOuterRadius);\n\
\n\
// Return empty colors if no intersection with the atmosphere geometry.\n\
if (primaryRayAtmosphereIntersect == czm_emptyRaySegment) {\n\
return;\n\
}\n\
\n\
// To deal with smaller values of PRIMARY_STEPS (e.g. 4)\n\
// we implement a split strategy: sky or horizon.\n\
// For performance reasons, instead of a if/else branch\n\
// a soft choice is implemented through a weight 0.0 <= w_stop_gt_lprl <= 1.0\n\
float x = 1e-7 * primaryRayAtmosphereIntersect.stop / length(primaryRayLength);\n\
// Value close to 0.0: close to the horizon\n\
// Value close to 1.0: above in the sky\n\
float w_stop_gt_lprl = 0.5 * (1.0 + czm_approximateTanh(x));\n\
\n\
// The ray should start from the first intersection with the outer atmopshere, or from the camera position, if it is inside the atmosphere.\n\
float start_0 = primaryRayAtmosphereIntersect.start;\n\
primaryRayAtmosphereIntersect.start = max(primaryRayAtmosphereIntersect.start, 0.0);\n\
// The ray should end at the exit from the atmosphere or at the distance to the vertex, whichever is smaller.\n\
primaryRayAtmosphereIntersect.stop = min(primaryRayAtmosphereIntersect.stop, length(primaryRayLength));\n\
\n\
// For the number of ray steps, distinguish inside or outside atmosphere (outer space)\n\
// (1) from outer space we have to use more ray steps to get a realistic rendering\n\
// (2) within atmosphere we need fewer steps for faster rendering\n\
float x_o_a = start_0 - ATMOSPHERE_THICKNESS; // ATMOSPHERE_THICKNESS used as an ad-hoc constant, no precise meaning here, only the order of magnitude matters\n\
float w_inside_atmosphere = 1.0 - 0.5 * (1.0 + czm_approximateTanh(x_o_a));\n\
int PRIMARY_STEPS = PRIMARY_STEPS_MAX - int(w_inside_atmosphere * 12.0); // Number of times the ray from the camera to the world position (primary ray) is sampled.\n\
int LIGHT_STEPS = LIGHT_STEPS_MAX - int(w_inside_atmosphere * 2.0); // Number of times the light is sampled from the light source's intersection with the atmosphere to a sample position on the primary ray.\n\
\n\
// Setup for sampling positions along the ray - starting from the intersection with the outer ring of the atmosphere.\n\
float rayPositionLength = primaryRayAtmosphereIntersect.start;\n\
// (1) Outside the atmosphere: constant rayStepLength\n\
// (2) Inside atmosphere: variable rayStepLength to compensate the rough rendering of the smaller number of ray steps\n\
float totalRayLength = primaryRayAtmosphereIntersect.stop - rayPositionLength;\n\
float rayStepLengthIncrease = w_inside_atmosphere * ((1.0 - w_stop_gt_lprl) * totalRayLength / (float(PRIMARY_STEPS * (PRIMARY_STEPS + 1)) / 2.0));\n\
float rayStepLength = max(1.0 - w_inside_atmosphere, w_stop_gt_lprl) * totalRayLength / max(7.0 * w_inside_atmosphere, float(PRIMARY_STEPS));\n\
\n\
vec3 rayleighAccumulation = vec3(0.0);\n\
vec3 mieAccumulation = vec3(0.0);\n\
vec2 opticalDepth = vec2(0.0);\n\
vec2 heightScale = vec2(czm_atmosphereRayleighScaleHeight, czm_atmosphereMieScaleHeight);\n\
\n\
// Sample positions on the primary ray.\n\
for (int i = 0; i < PRIMARY_STEPS_MAX; ++i) {\n\
\n\
// The loop should be: for (int i = 0; i < PRIMARY_STEPS; ++i) {...} but WebGL1 cannot\n\
// loop with non-constant condition, so it has to break early instead\n\
if (i >= PRIMARY_STEPS) {\n\
break;\n\
}\n\
\n\
// Calculate sample position along viewpoint ray.\n\
vec3 samplePosition = primaryRay.origin + primaryRay.direction * (rayPositionLength + rayStepLength);\n\
\n\
// Calculate height of sample position above ellipsoid.\n\
float sampleHeight = length(samplePosition) - atmosphereInnerRadius;\n\
\n\
// Calculate and accumulate density of particles at the sample position.\n\
vec2 sampleDensity = exp(-sampleHeight / heightScale) * rayStepLength;\n\
opticalDepth += sampleDensity;\n\
\n\
// Generate ray from the sample position segment to the light source, up to the outer ring of the atmosphere.\n\
czm_ray lightRay = czm_ray(samplePosition, lightDirection);\n\
czm_raySegment lightRayAtmosphereIntersect = czm_raySphereIntersectionInterval(lightRay, origin, atmosphereOuterRadius);\n\
\n\
float lightStepLength = lightRayAtmosphereIntersect.stop / float(LIGHT_STEPS);\n\
float lightPositionLength = 0.0;\n\
\n\
vec2 lightOpticalDepth = vec2(0.0);\n\
\n\
// Sample positions along the light ray, to accumulate incidence of light on the latest sample segment.\n\
for (int j = 0; j < LIGHT_STEPS_MAX; ++j) {\n\
\n\
// The loop should be: for (int j = 0; i < LIGHT_STEPS; ++j) {...} but WebGL1 cannot\n\
// loop with non-constant condition, so it has to break early instead\n\
if (j >= LIGHT_STEPS) {\n\
break;\n\
}\n\
\n\
// Calculate sample position along light ray.\n\
vec3 lightPosition = samplePosition + lightDirection * (lightPositionLength + lightStepLength * 0.5);\n\
\n\
// Calculate height of the light sample position above ellipsoid.\n\
float lightHeight = length(lightPosition) - atmosphereInnerRadius;\n\
\n\
// Calculate density of photons at the light sample position.\n\
lightOpticalDepth += exp(-lightHeight / heightScale) * lightStepLength;\n\
\n\
// Increment distance on light ray.\n\
lightPositionLength += lightStepLength;\n\
}\n\
\n\
// Compute attenuation via the primary ray and the light ray.\n\
vec3 attenuation = exp(-((czm_atmosphereMieCoefficient * (opticalDepth.y + lightOpticalDepth.y)) + (czm_atmosphereRayleighCoefficient * (opticalDepth.x + lightOpticalDepth.x))));\n\
\n\
// Accumulate the scattering.\n\
rayleighAccumulation += sampleDensity.x * attenuation;\n\
mieAccumulation += sampleDensity.y * attenuation;\n\
\n\
// Increment distance on primary ray.\n\
rayPositionLength += (rayStepLength += rayStepLengthIncrease);\n\
}\n\
\n\
// Compute the scattering amount.\n\
rayleighColor = czm_atmosphereRayleighCoefficient * rayleighAccumulation;\n\
mieColor = czm_atmosphereMieCoefficient * mieAccumulation;\n\
\n\
// Compute the transmittance i.e. how much light is passing through the atmosphere.\n\
opacity = length(exp(-((czm_atmosphereMieCoefficient * opticalDepth.y) + (czm_atmosphereRayleighCoefficient * opticalDepth.x))));\n\
}\n\
";
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