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Atmospheric Scattering Issue (GLSL)

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#1 multifractal   Members   


Posted 05 July 2013 - 01:49 AM


recently I have been trying to implement Sean O'Neil's atmospheric scattering shaders into a java project I have been working on (using jmonkey engine). I have the atmosphere from space shader working perfectly but for some reason I cannot get the ground from space shader working correctly. To see the planet at all I have to up the number of samples taken to ~400 and this is terribly inefficient and causes the color of the planet to be far too...orange. If anyone has any insight on this I would be extremely appreciative. I will include (what I think is relevant) relevant code/shaders. Thanks so much for the time!

The result I am getting using a diffuse color of (.85,.85,.85):

(what the color actually looks like sans shading: color.png )






Starting here is how I render the spheres: 

sun = new DirectionalLight();
		 Vector3f LIGHT_DIRECTION = new Vector3f(0.5f, 0.5f, -0.5f).normalize();
		Mesh plan = makePlanet();
		pla = new Geometry("Mesh" , plan);
		mat_P = new Material(assetManager, "GroundFromSpace.j3md");
		Mesh atmosphere = makeAtmosphere();
		atm = new Geometry("Mesh", atmosphere);
		mat_A = new Material(assetManager, "SkyFromSpace.j3md");

public Mesh makePlanet(){
	planet = new Planet(4, new Vector3f(0,0,0));
	Mesh pl = new Sphere(128,128,planet.getRadius());
	return pl;

public Mesh makeAtmosphere(){
	Mesh atmosphere = new Sphere(128, 128, planet.getOuterRadius());
	return atmosphere;

the "Planet Class" simply contains all of the parameters (which I have checked many times to match them to O'Neil's). The setUpMaterial methods simply fetch these variables and pass them along to the shaders. 


Here is the vertex shader (GroundFromSpace):

uniform mat4 g_WorldViewProjectionMatrix;
uniform mat4 g_WorldMatrix;
uniform vec3 m_v3CameraPos;		// The camera's current position
uniform vec3 m_v3LightPos;		// The direction vector to the light source
uniform vec3 m_v3InvWavelength;	// 1 / pow(wavelength, 4) for the red, green, and blue channels
uniform float m_fCameraHeight;	// The camera's current height
uniform float m_fCameraHeight2;	// fCameraHeight^2
uniform float m_fOuterRadius;		// The outer (atmosphere) radius
uniform float m_fOuterRadius2;	// fOuterRadius^2
uniform float m_fInnerRadius;		// The inner (planetary) radius
uniform float m_fInnerRadius2;	// fInnerRadius^2
uniform float m_fKrESun;			// Kr * ESun
uniform float m_fKmESun;			// Km * ESun
uniform float m_fKr4PI;			// Kr * 4 * PI
uniform float m_fKm4PI;			// Km * 4 * PI
uniform float m_fScale;			// 1 / (fOuterRadius - fInnerRadius)
uniform float m_fScaleDepth;		// The scale depth (i.e. the altitude at which the atmosphere's average density is found)
uniform float m_fScaleOverScaleDepth;	// fScale / fScaleDepth
attribute vec4 inPosition;
uniform int m_nSamples;
uniform float m_fSamples;
varying vec4 c1;
varying vec4 c0;

float scale(float fCos)
	float x = 1.0 - fCos;
	return m_fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));

void main(void)
	// 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 v3Pos = vec3(g_WorldMatrix * inPosition);
	vec3 v3Ray = v3Pos - m_v3CameraPos;
	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(m_v3CameraPos, v3Ray);
	float C = m_fCameraHeight2 - m_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 = m_v3CameraPos + v3Ray * fNear;
	fFar -= fNear;
	float fDepth = exp((m_fInnerRadius - m_fOuterRadius) / m_fScaleDepth);
	float fCameraAngle = dot(-v3Ray, v3Pos) / length(v3Pos);
	float fLightAngle = dot(m_v3LightPos, v3Pos) / length(v3Pos);
	float fCameraScale = scale(fCameraAngle);
	float fLightScale = scale(fLightAngle);
	float fCameraOffset = fDepth*fCameraScale;
	float fTemp = (fLightScale + fCameraScale);

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

	// Now loop through the sample rays
	vec3 v3FrontColor = vec3(0.0, 0.0, 0.0);
	vec3 v3Attenuate;
	for(int i=0; i<m_nSamples; i++)
		float fHeight = length(v3SamplePoint);
		float fDepth = exp(m_fScaleOverScaleDepth * (m_fInnerRadius - fHeight));
		float fScatter = fDepth*fTemp - fCameraOffset;
		v3Attenuate = exp(-fScatter * (m_v3InvWavelength * m_fKr4PI + m_fKm4PI));
		v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
		v3SamplePoint += v3SampleRay;

	gl_FrontColor = vec4(v3FrontColor * (m_v3InvWavelength * m_fKrESun + m_fKmESun),1.0);
	gl_FrontSecondaryColor = vec4(v3Attenuate,1.0);
	gl_Position = g_WorldViewProjectionMatrix * inPosition;


and here is the pixel shader (note that inColor is jmonkey's version of gl_Color and inPosition^^ is their version of gl_Vertex):

attribute vec4 inColor;
varying vec4 c0, c1;
void main (void)
	gl_FragColor = inColor + 0.85 * gl_SecondaryColor;

Again, thanks a lot for the time, any help whatsoever is appreciated. 

Edited by multifractal, 06 July 2013 - 06:39 AM.

#2 multifractal   Members   


Posted 06 July 2013 - 06:39 AM

UPDATE: I solved the issue. It was a simple careless mistake: I wasn't passing the square of outer radius into the shader. That fixed it all functioned as it should. Thanks for the consideration, 

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