Particle Systems

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Particle Systems

• Bryan Duggan

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Introduction

• Sometimes instead of modelling a complex object
  with many vertices, we need to model
• Lots of small objects each with a single vertex
• This is called a particle system
• There are lots of applications for particle
  systems

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(No Transcript)
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Example uses

• Dust from a moving vehicle
• Snow
• Exhaust jets
• Blood gushing out
• Fire
• Sparks

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Requirements

• Keep track of lots of particles
• Create new particles (sometimes using random
  attributes)
• Update each particle
• Using the laws of physics
• Render each one
• When particles die, create new ones

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Refresher on Vertex Buffers

• A chunk of contiguous memory that contains vertex
  data
• A place to hold the vertices we want to draw.
• Can be placed in VRAM for faster rendering
• Represented by a IDirect3DVertexBuffer9 object

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You decide the format of the vertex

• Depending on whether you want colour, texturing
  etc.
• E.g.
• struct Vertex
• Vertex()
• Vertex(float x, float y, float z)
• _x x _y y _z z
• float _x, _y, _z
• static const DWORD FVF
• const DWORD VertexFVF D3DFVF_XYZ

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Vertices with colours

• struct ColorVertex
• ColorVertex()
• ColorVertex(float x, float y, float z, D3DCOLOR
  c)
• _x x _y y _z z _color c
• float _x, _y, _z
• D3DCOLOR _color
• static const DWORD FVF
• const DWORD ColorVertexFVF D3DFVF_XYZ
  D3DFVF_DIFFUSE

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Vertices with textures

• struct TexelVertex
• TexelVertex()
• TexelVertex(float x, float y, float z, float u,
  float v)
• _x x _y y _z z
• _u u _v v
• float _x, _y, _z
• float _u, _v
• static const DWORD FVF
• const DWORD TexelVertexFVF D3DFVF_XYZ
  D3DFVF_TEX1

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To create one

• HRESULT CreateVertexBuffer(      
• UINT Length,     DWORD Usage,DWORD FVF,
  D3DPOOL Pool,     IDirect3DVertexBuffer9 ppVer
  texBuffer, HANDLE pSharedHandle
• )
• Length Number of bytes (number_of_vertices
  sizeof(Vertex)
• Usage Well usually use D3DUSAGE_WRITEONLY
• FVF Flexible vertex format The static member
  of the struct
• Pool - D3DPOOL_MANAGED Let DirectX manage the
  pool
• pSharedHandle Usually 0

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Example

• device-gtCreateVertexBuffer(
• 36 sizeof(TexelVertex), // size in bytes
• D3DUSAGE_WRITEONLY, // flags
• TexelVertexFVF, // vertex format
• D3DPOOL_MANAGED, // managed memory pool
• _landscapeVertices,// return create vertex
  buffer
• 0
• )

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To write to the buffer

• Obtain a pointer to the contents by
• Vertex vertices
• IDirect3DVertexBuffer9Lock(
• UINT Offset,
• UNIT size,
• BYTE vertices,
• DWORD flags
• )
• Offset Offset in bytes from the start of the
  buffer
• Size Number of bytes to lock
• vertices Pointer to the start of the locked
  data. We can write to this pointer after we lock
  the buffer
• Flags Usually 0.
• E.g.
• landscapeVertices-gtLock(0, 0, (void)vertices,
  0)
• vertices0 Vertex(1,2,3)
• vertices1 Vertex(1,2,3)

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To draw the buffer

• Set the vertex stream source
• device-gtSetStreamSource(0, _landscapeVertices,
  0, sizeof(Vertex))
• Set the format of the stream
• device-gtSetFVF(VertexFVF)
• Perform any transformations necessary
• D3DXMATRIX landscapeScale
• D3DXMatrixScaling(landscapeScale, 1,1,1)
• device-gtSetTransform(D3DTS_WORLD,
  landscapeScale)
• Draw the vertices
• device-gtDrawPrimitive(D3DPT_TRIANGLELIST, 0, 2)

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The Particle Class

• class Particlepublic MoveableEntity
• protected
• int _size
• D3DCOLOR _colour
• float _duration
• float _age
• public
• Particle()
• void update(float timeDelta)
• int getSize()
• void setSize(int size)
• D3DCOLOR getColour()
• void setColour(D3DCOLOR colour)
• float getAge()
• void setAge(float age)

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The ParticleSystem class

• class ParticleSystempublic MoveableEntity,
  public DrawableEntity
• private
• Particle _particles
• long _numParticles
• IDirect3DVertexBuffer9 _vertices
• IDirect3DTexture9 _texture
• float _size
• stdstring _textureName
• public
• ParticleSystem()
• ParticleSystem(int numParticles)
• ParticleSystem()
• bool setup(IDirect3DDevice9 device)
• void update(float timeDelta)
• void draw(IDirect3DDevice9 device)
• void cleanup(IDirect3DDevice9 device)
• void initParticle(Particle particle)

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New FVF

• struct ParticleVertex
• ParticleVertex(float x, float y, float z,
  D3DCOLOR c)
• _x x _y y _z z _color c
• ParticleVertex()
• _x _y _z 0
• _color 0
• float _x, _y, _z
• D3DCOLOR _color
• static const DWORD FVF

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Point Sprites

• A vertex
• But rendered with a texture in place of every
  vertex
• Create a vertex buffer of ParticleVertexs

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To render

• device-gtSetRenderState(D3DRS_LIGHTING, false)
• device-gtSetRenderState(D3DRS_POINTSPRITEENABLE,
  true)
• device-gtSetRenderState(D3DRS_POINTSCALEENABLE,
  true)
• device-gtSetRenderState(D3DRS_POINTSIZE,
  FtoDw(_size))
• device-gtSetRenderState(D3DRS_POINTSIZE_MIN,
  FtoDw(0.0f))
• // control the size of the particle relative to
  distance
• device-gtSetRenderState(D3DRS_POINTSCALE_A,
  FtoDw(0.0f))
• device-gtSetRenderState(D3DRS_POINTSCALE_B,
  FtoDw(0.0f))
• device-gtSetRenderState(D3DRS_POINTSCALE_C,
  FtoDw(1.0f))
• // use alpha from texture
• device-gtSetTextureStageState(0,
  D3DTSS_ALPHAARG1, D3DTA_TEXTURE)
• device-gtSetTextureStageState(0, D3DTSS_ALPHAOP,
  D3DTOP_SELECTARG1)
• device-gtSetRenderState(D3DRS_ALPHABLENDENABLE,
  true)
• device-gtSetRenderState(D3DRS_SRCBLEND,
  D3DBLEND_SRCALPHA)
• device-gtSetRenderState(D3DRS_DESTBLEND,
  D3DBLEND_INVSRCALPHA)

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Setting up the particle system

• _numParticles numParticles
• _particles new Particle_numParticles
• _vertices NULL
• _texture NULL
• _size 0.25f
• for (int i 0 i lt _numParticles i )
• initParticle( _particlesi)

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• bool ParticleSystemsetup(IDirect3DDevice9
  device)
• _device device
• device-gtCreateVertexBuffer(_numParticles
  sizeof(ParticleVertex), 0, ParticleVertexFVF,
  D3DPOOL_DEFAULT, _vertices, NULL)
• _texture AssetLoaderinstance()-gtgetTexture(_t
  extureName.c_str(), device)
• return true

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Initialise a new particle

• void ParticleSysteminitParticle(Particle
  particle)
• // printf("New particle!\n")
• // Reset the particle
• particle-gtsetPosition( D3DXVECTOR3(10, 0, 10))
• D3DXVECTOR3 newLook
• newLook.x getRandomFloat(-1.0f, 1.0f)
• newLook.y getRandomFloat(-1.0f, 1.0f)
• newLook.z getRandomFloat(-1.0f, 1.0f)
• particle-gtsetLook( newLook)
• particle-gtsetColour(D3DXCOLOR(
• getRandomFloat(0.0f, 1.0f),
• getRandomFloat(0.0f, 1.0f),
• getRandomFloat(0.0f, 1.0f),
• 1.0f))
• particle-gtsetSpeed(getRandomFloat(1.0f, 5.0f))
• particle-gtsetDuration(getRandomFloat(1.0f,
  5.0f))

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Update

• for(int i 0 i lt _numParticles i)
• if(_particlesi.getAge() gt _particlesi.getDu
  ration())
• initParticle( _particlesi)
• _particlesi.update(timeDelta)

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Things to try

• Change the particle system to use
• Random Acceleration instead of just random
  velocity
• Change the particle system so that they all die
  at the same time (to make an explosion)
• Change the particle system to make an explosion
  up from the ground (the particles only shoot
  upwards
• Change the particle system to simulate snow