I have been trying to add a particle system to my Directx11 graphics demo, and so i have been using the 'Introduction to 3d Game Programming with directx 11' book.
Because of this am attempting to use a HLSL StreamOut technique to update the particle system and a separate technique to render the particles.
Below is the HLSL code for the particle system, i have tried adjusting the acceleration and velocity in the off chance the speed was sending the particles off the screen, however this had no effect.
cbuffer cbPerFrame
{
float3 gEyePosW;
float3 gEmitPosW;
float3 gEmitDirW;
float gGameTime;
float gTimeStep;
float4x4 gViewProj;
};
cbuffer cbFixed
{
// Net constant acceleration used to accerlate the particles.
float3 gAccelW = {0.0f, 0.2f, 0.0f};
// Texture coordinates for billbording are always the same - we use a qquad in this effect :)
float2 gTexC[4] =
{
float2(0.0f, 1.0f),
float2(0.0f, 0.0f),
float2(1.0f, 1.0f),
float2(1.0f, 0.0f)
};
};
// Nonnumeric values cannot be added to a cbuffer.
Texture2DArray gTextureMapArray;
// Random texture used to generate random numbers in shaders.
Texture1D gRandomTexture;
SamplerState samLinear
{
Filter = MIN_MAG_MIP_LINEAR;
AddressU = WRAP;
AddressV = WRAP;
};
DepthStencilState DisableDepth
{
DepthEnable = FALSE;
DepthWriteMask = ZERO;
};
DepthStencilState NoDepthWrites
{
DepthEnable = TRUE;
DepthWriteMask = ZERO;
};
BlendState AdditiveBlending
{
AlphaToCoverageEnable = FALSE;
BlendEnable[0] = TRUE;
SrcBlend = SRC_ALPHA;
DestBlend = ONE;
BlendOp = ADD;
SrcBlendAlpha = ZERO;
DestBlendAlpha = ZERO;
BlendOpAlpha = ADD;
RenderTargetWriteMask[0] = 0x0F;
};
///////////////////////////////////////////////////////////////
// Helper functions
//
///////////////////////////////////////////////////////////////
float3 RandUnitVec3(float offset)
{
// Use game time plus offset to sample random texture.
float u = (gGameTime + offset);
// coordinates in [-1,1]
float3 v = gRandomTexture.SampleLevel(samLinear, u, 0).xyz;
// project onto unit sphere (Normalize)
return normalize(v);
}
///////////////////////////////////////////////////////////////
// Stream Out Technique
//
///////////////////////////////////////////////////////////////
#define PT_EMITTER 0
#define PT_FLARE 1
struct Particle
{
float3 InitPosW : POSITION;
float3 InitVelW : VELOCITY;
float2 SizeW : SIZE;
float Age : AGE;
uint Type : Type;
};
Particle StreamOutVS(Particle vin)
{
return vin;
}
// The stream-out GS is just responsible for emitting
// new particles and destroying old particles. The logic
// programed here will generally vary from particle system
// to particle system, as the destroy/spawn rules will be
// different.
[maxvertexcount(2)]
void StreamOutGS(point Particle gin[1],
inout PointStream<Particle> ptStream)
{
gin[0].Age += gTimeStep;
// if particle is emitter particle
if (gin[0].Type == PT_EMITTER)
{
// If it's time to emit new particle
if (gin[0].Age > 0.005f)
{
float3 vRandom = RandUnitVec3(0.0f);
vRandom.x *= 0.5f;
vRandom.z *= 0.5f;
Particle p;
p.InitPosW = gEmitPosW.xyz;
p.InitVelW = 0.5f*vRandom;
p.SizeW = float2(3.0f, 3.0f);
p.Age = 0.0f;
p.Type = PT_FLARE;
ptStream.Append(p);
// reset the time to emit
gin[0].Age = 0.0f;
}
// always keep emitters
ptStream.Append(gin[0]);
}
else
{
// Set conditions to keep a particle - in this case age limit
if (gin[0].Age <= 1.0f)
{
ptStream.Append(gin[0]);
}
}
}
GeometryShader gsStreamOut = ConstructGSWithSO(
CompileShader( gs_5_0, StreamOutGS() ),
"POSITION.xyz; VELOCITY.xyz; SIZE.xyz; AGE.x; TYPE.x" );
technique11 StreamOutTech
{
pass P0
{
SetVertexShader( CompileShader( vs_5_0, StreamOutVS() ) );
SetGeometryShader( gsStreamOut );
// disable pixel shader for stream-out only
SetPixelShader(NULL);
// we must also disable the depth buffer for stream-out only
SetDepthStencilState( DisableDepth, 0 );
}
}
///////////////////////////////////////////////////////////////
// Draw Technique
//
///////////////////////////////////////////////////////////////
struct VertexIn
{
float3 Pos : POSITION;
float2 SizeW : SIZE;
};
struct VertexOut
{
float3 PosW : POSITION;
float2 SizeW : SIZE;
float4 Colour : COLOR;
uint Type : TYPE;
};
VertexOut DrawVS(Particle vin)
{
VertexOut vout;
float t = vin.Age;
// constant Acceleration equation
vout.PosW = 0.5f*t*t*gAccelW + t*vin.InitVelW + vin.InitPosW;
// fade colour with time
float opacity = 1.0f - smoothstep(0.0f, 1.0f, t/1.0f);
vout.Colour = float4(1.0f, 1.0f, 1.0f, opacity);
vout.SizeW = vin.SizeW;
vout.Type = vin.Type;
return vout;
}
struct GeoOut
{
float4 PosH : SV_POSITION;
float4 Colour : COLOR;
float2 Tex : TEXCOORD;
};
// Expand each 'Point' into a quad (4 verticies)
[maxvertexcount(4)]
void DrawGS(point VertexOut gin[1],
inout TriangleStream<GeoOut> triStream)
{
// Do not draw Emiter particles in this system
if (gin[0].Type != PT_EMITTER)
{
//
// Compute world matrix so that billboard faces the camera.
//
float3 look = normalize(gEyePosW.xyz - gin[0].PosW);
float3 right = normalize(cross(float3(0,1,0), look));
float3 up = cross(look, right);
//
// Compute triangle strip vertices (quad) in world space.
//
float halfWidth = 0.5f*gin[0].SizeW.x;
float halfHeight = 0.5f*gin[0].SizeW.y;
float4 v[4];
v[0] = float4(gin[0].PosW + halfWidth*right - halfHeight*up, 1.0f);
v[1] = float4(gin[0].PosW + halfWidth*right + halfHeight*up, 1.0f);
v[2] = float4(gin[0].PosW - halfWidth*right - halfHeight*up, 1.0f);
v[3] = float4(gin[0].PosW - halfWidth*right + halfHeight*up, 1.0f);
//
// Transform quad vertices to world space and output
// them as a triangle strip.
//
GeoOut gout;
[unroll]
for(int i = 0; i < 4; ++i)
{
gout.PosH = mul(v[i], gViewProj);
gout.Tex = gTexC[i];
gout.Colour = gin[0].Colour;
triStream.Append(gout);
}
}
}
float DrawPS(GeoOut pin) : SV_TARGET
{
return gTextureMapArray.Sample(samLinear, float3(pin.Tex, 0)) * pin.Colour;
}
technique11 DrawTech
{
pass P0
{
SetVertexShader( CompileShader( vs_5_0, DrawVS() ) );
SetGeometryShader( CompileShader( gs_5_0, DrawGS() ) );
SetPixelShader( CompileShader( ps_5_0, DrawPS() ) );
SetBlendState(AdditiveBlending, float4(0.0f, 0.0f, 0.0f, 0.0f), 0xffffffff);
SetDepthStencilState( NoDepthWrites, 0 );
}
}Below is the code for building the VB.
void ParticleSystem::BuildVB(ID3D11Device* device)
{
/////////////////////////////////////////////////////////
// Create the buffer to start the particle system.
/////////////////////////////////////////////////////////
D3D11_BUFFER_DESC vbd;
vbd.Usage = D3D11_USAGE_DEFAULT;
vbd.ByteWidth = sizeof(Vertex::Particle) * 1;
vbd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
vbd.CPUAccessFlags = 0;
vbd.MiscFlags = 0;
vbd.StructureByteStride = 0;
// The initial particle emitter has type 0 and age 0. The rest
// of the particle attributes do not apply to an emitter.
Vertex::Particle p;
ZeroMemory(&p, sizeof(Vertex::Particle));
p.Age = 0.0f;
p.Type = 0;
D3D11_SUBRESOURCE_DATA vinitData;
vinitData.pSysMem = &p;
HR(device->CreateBuffer(&vbd, &vinitData, &mInitVB));
//////////////////////////////////////////////////////////////
// Create the buffers which swap back and forth for stream-out and drawing.
//////////////////////////////////////////////////////////////
vbd.ByteWidth = sizeof(Vertex::Particle) * mMaxParticles;
vbd.BindFlags = D3D11_BIND_VERTEX_BUFFER | D3D11_BIND_STREAM_OUTPUT;
HR(device->CreateBuffer(&vbd, 0, &mDrawVB));
HR(device->CreateBuffer(&vbd, 0, &mStreamOutVB));
}And now the Draw cpp code.
void ParticleSystem::Draw(ID3D11DeviceContext* dc, const XMMATRIX& viewProj)
{
//
// Set constants.
//
mFX->SetViewProj(viewProj);
mFX->SetGameTime(mGameTime);
mFX->SetTimeStep(mTimeStep);
mFX->SetEyePosW(mEyePosW);
mFX->SetEmitPosW(mEmitPosW);
mFX->SetEmitDirW(mEmitDirW);
mFX->SetTexArray(mTextureArraySRV);
mFX->SetRandomTex(mRandomTextureSRV);
//
// Set IA stage.
//
dc->IASetInputLayout(InputLayouts::Particle);
dc->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_POINTLIST);
UINT stride = sizeof(Vertex::Particle);
UINT offset = 0;
// On the first pass, use the initialization VB. Otherwise, use
// the VB that contains the current particle list.
if( mFirstRun )
dc->IASetVertexBuffers(0, 1, &mInitVB, &stride, &offset);
else
dc->IASetVertexBuffers(0, 1, &mDrawVB, &stride, &offset);
//
// Draw the current particle list using stream-out only to update them.
// The updated vertices are streamed-out to the target VB.
//
dc->SOSetTargets(1, &mStreamOutVB, &offset);
D3DX11_TECHNIQUE_DESC techDesc;
mFX->StreamOutTech->GetDesc( &techDesc );
for(UINT p = 0; p < techDesc.Passes; ++p)
{
mFX->StreamOutTech->GetPassByIndex( p )->Apply(0, dc);
if(mFirstRun)
{
dc->Draw(1, 0);
mFirstRun = false;
}
else
{
dc->DrawAuto();
}
}
// done streaming-out--unbind the vertex buffer
ID3D11Buffer* bufferArray[1] = {0};
dc->SOSetTargets(1, bufferArray, &offset);
// ping-pong the vertex buffers
std::swap(mDrawVB, mStreamOutVB);
//
// Draw the updated particle system we just streamed-out.
//
dc->IASetVertexBuffers(0, 1, &mDrawVB, &stride, &offset);
mFX->DrawTech->GetDesc( &techDesc );
for(UINT p = 0; p < techDesc.Passes; ++p)
{
mFX->DrawTech->GetPassByIndex( p )->Apply(0, dc);
dc->DrawAuto();
}
}I had thought that perhaps either a blend state or Depth state in use by some of the other objects in my scene may be causing the issue, (perhaps i have misunderstood something I have set earlier). I tried removing all other render code leaving just the draw code above, but with no results.
To my mind, I can only think of a few possible causes for the issue i am having, but so far i am unable to find a solution.
- The scale of the system is wrong for my scene. eg. the particles are drawing but are moving off the screen to fast to be seen.
- As mentioned above i have tried removing the acceleration and velocity of the particles in the HLSL code, in order to see stationary particles. This had no effect.
- Blend state/Depth stencil state is incorrect. Eg. As mentioned above.
- The Emitter particle is, for some reason, not being produced/placed correctly. causing no 'drawable' particles to be produced in turn. As most of this code is in the .fx file, I am unable to step through to check the emitter particles. I think this is the more likely issue, but i have been wrong before.
Any help on this would be greatly appreciated, I am well and truly stuck on this. Below I have added additional snippets of code which may be of use.
E.G. Input layout.
const D3D11_INPUT_ELEMENT_DESC InputLayoutDesc::Particle[5] =
{
{"POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0},
{"VELOCITY", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 12, D3D11_INPUT_PER_VERTEX_DATA, 0},
{"SIZE", 0, DXGI_FORMAT_R32G32_FLOAT, 0, 24, D3D11_INPUT_PER_VERTEX_DATA, 0},
{"AGE", 0, DXGI_FORMAT_R32_FLOAT, 0, 32, D3D11_INPUT_PER_VERTEX_DATA, 0},
{"TYPE", 0, DXGI_FORMAT_R32_UINT, 0, 36, D3D11_INPUT_PER_VERTEX_DATA, 0},
};And particle system INIT
mFire.Init(md3dDevice, AppEffects::FireFX, mFlareTextureSRV, mRandomTextureSRV, 500);
mFire.SetEmitPos(XMFLOAT3(1.0f, 0.5f, 0.0f));
void ParticleSystem::Init(ID3D11Device* device, ParticleEffect* fx,
ID3D11ShaderResourceView* textureArraySRV,
ID3D11ShaderResourceView* randomTextureSRV,
UINT maxParticles)
{
mMaxParticles = maxParticles;
mFX = fx;
mTextureArraySRV = textureArraySRV;
mRandomTextureSRV = randomTextureSRV;
BuildVB(device);
}If i have missed any section of the code you would need to see, let me know.
Thanks in advance.
