vert shader

#version 150

uniform mat4 ciModelViewProjection;

uniform mat4 ciProjectionMatrix;

uniform mat4 ciModelViewMatrix;
in vec4 ciPosition;

uniform vec3 v3LightPosition;	// The direction vector to the light source
uniform vec3 cameraPosition;
uniform vec3 v3InvWavelength;	// 1 / pow(wavelength, 4) for the red, green, and blue 
//uniform float fCameraHeight;	// The camera's current height
uniform float fCameraHeight2;	// fCameraHeight^2
uniform float fOuterRadius;		// The outer (atmosphere) radius
uniform float fOuterRadius2;	// fOuterRadius^2
uniform float fInnerRadius;		// The inner (planetary) radius
uniform float fInnerRadius2;	// fInnerRadius^2
uniform float fKrESun;			// Kr * ESun
uniform float fKmESun;			// Km * ESun
uniform float fKr4PI;			// Kr * 4 * PI
uniform float fKm4PI;			// Km * 4 * PI
uniform float fScale;			// 1 / (fOuterRadius - fInnerRadius)
uniform float fScaleDepth;		// The scale depth (i.e. the altitude at which the atmosphere's average density is found)
uniform float fScaleOverScaleDepth;	// fScale / fScaleDepth

const int nSamples = 3;
const float fSamples = 3.0;

out vec3 v3Direction;
out vec3 c0;
out vec3 c1;
out vec3 v3LightDirection;


float scale(float fCos)
{
	float x = 1.0 - fCos;

	return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
}

void main(void)
{
	v3LightDirection=v3LightPosition/length(v3LightPosition);
	// Get the ray from the camera to the vertex and its length (which is the far point of the ray passing through the atmosphere)
	vec3 v3Ray = ciPosition.xyz - cameraPosition;
	float fFar = length(v3Ray);
	v3Ray /= fFar;

	// Calculate the closest intersection of the ray with the outer atmosphere (which is the near point of the ray passing through the atmosphere)
	float B = 2.0 * dot(cameraPosition, v3Ray);
	float C = fCameraHeight2 - fOuterRadius2;
	float fDet = max(0.0, B*B - 4.0 * C);
	float fNear = 0.5 * (-B - sqrt(fDet));

	// Calculate the ray's starting position, then calculate its scattering offset
	vec3 v3Start = cameraPosition + v3Ray * fNear;
	fFar -= fNear;
	float fStartAngle = dot(v3Ray, v3Start) / fOuterRadius;
	float fStartDepth = exp(-1.0 / fScaleDepth);
	float fStartOffset = fStartDepth * scale(fStartAngle);
	//c0 = vec3(1.0, 0, 0) * fStartAngle;

	// Initialize the scattering loop variables
	float fSampleLength = fFar / fSamples;
	float fScaledLength = fSampleLength * fScale;
	vec3 v3SampleRay = v3Ray * fSampleLength;
	vec3 v3SamplePoint = v3Start + v3SampleRay * 0.5;

	//gl_FrontColor = vec4(0.0, 0.0, 0.0, 0.0);

	// Now loop through the sample rays
	vec3 v3FrontColor = vec3(0.0, 0.0, 0.0);
	for(int i=0; i<nSamples; i++)
	{
		float fHeight = length(v3SamplePoint);
		float fDepth = exp(fScaleOverScaleDepth *(fInnerRadius - fHeight));
		
		float fLightAngle = dot(v3LightPosition, v3SamplePoint) / fHeight;
		float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight;
		float fScatter = (fStartOffset + fDepth * (scale(fLightAngle) - scale(fCameraAngle)));
		vec3 v3Attenuate = exp(-fScatter * (v3InvWavelength * fKr4PI + fKm4PI));
		v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
		v3SamplePoint += v3SampleRay;
	
	}
	// Finally, scale the Mie and Rayleigh colors and set up the varying variables for the pixel shader
	gl_Position =  ciModelViewProjection *  ciPosition;
	c0 = v3FrontColor * (v3InvWavelength * fKrESun);
	c1 = v3FrontColor * fKmESun;

	v3Direction = cameraPosition - ciPosition.xyz;
}