AdvancedParticleSystem Class Reference

Implements a hierarchical particle system. More...

List of all members.

Public Member Functions
void	Display (Camera *cam, Vector LightPos)
	renders the particle system from the given camera using the given light position
void	Refresh (Camera *cam, Vector LightPos, unsigned int Dt, unsigned int TimefromSecond)
	refreshes the particle system
void	RefreshDepths (Camera *cam)
	generates front and back depth textures od the smaller particle system
void	Initialize ()
	initialize textures and gpu programs
void	InitSystems ()
	initialize the two particle systems
void	RenderObjectDepths (Camera *cam)
	generates scene depth texture
void	RefreshIllumTextures (Vector LightPos)
	refreshes the illumination texture
Public Attributes
float	albedo
	albedo of the particles
float	symmetry
	scattering symmetry of the scattering (used in phase function calculation)
float	transparency
	transparency of the particles
ParticleSystem	m_ParticleSystem
	particle system made ot of a smaller system
ParticleSystem	m_LittleParticleSystem
	smaller particle system
Private Attributes
Impostor	m_DisplayImpostor
	Impostor to display.
Impostor	m_IllumImpostor
	Impostor for illumination calculation.
RenderTexture	m_IllumTexture
	Illumination texture.
RenderTexture	m_FrontDepthTexture
	Stores nearest and furthest distances of the particles from the camera and also the opacity.
RenderTexture	m_ObjectsTexture
	Stores nearest distances of the scene objects from the camera.
RenderTexture	m_ScatteredIlumTexture
	A motion blurred version of the illumination texture to avoid abrupt changes.

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Detailed Description

Implements a hierarchical particle system.

A hierarchical particle system is a particle system made out of a smaller particle systems. First an image of the smaller particle system should be rendered, than this image can be multiplied and be used as sprite images to form the bigger system.

To avoid incorrect depth culling caused by the simplifications made by considering a group of particles as a single quad we have to take into acount some additional depth information too. We also render the the closest and the furthest depth values of the smaller system in the view camera's space. During display this depth information can be used to estimate the length of the light ray segment travelled in the medium and alter the opacity of the particles respectively.

This particle system implementation also deals with light scattering inside the medium. It builds a layered light absorption texture which stores the amount of absorped light in different depths from lightsource. With the use of the illumination texture we can approximate self shadowing of the medium. This implementation uses four layers and stores it in the four channels of a texture. This way no 3D textures are needed, and the light absorption (illumination) texture can be generated in a single render pass.

During rendering a mie scattering model is used to compute the amount of scattered light. To speed up calculations phase function values are read back from a 2D look-up texture (phase texture).

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Member Function Documentation

void AdvancedParticleSystem::RefreshIllumTextures (  Vector  LightPos  )

refreshes the illumination texture The illumination texture is a four layered texture, each layer stored in the separate color channels.

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