Advertisement Jump to content
Sign in to follow this  
relaxok

HLSL - Billboarding a mesh

This topic is 1774 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Guys:

 

I have a vertex shader that I use for all my non-terrain models.  My per-mesh structure has a flags uint where i can set things like billboard, unlit, etc.  Some models have single meshes that need to be billboarded, like a light halo that looks the same from any angle.  However, I can't figure out how to successfully billboard the mesh.

 

Below is my vertex shader.. in the billboard section I've tried various combinations of matrices as you can see.. based on MJP's response in this topic:  

 

http://www.gamedev.net/topic/507808-hlsl-billboard/


PixelInputType VS(VertexInputType input, uint InstanceID : SV_InstanceID )
{	
	PixelInputType output;
    
	// Fix w
        input.position.w = 1.0f;

	// Calculate animation matrices
	matrix bonematrix = ( float( input.boneweight0 ) / 255.0f ) *  BoneMatrices[ input.boneindex0 ];
	bonematrix += ( float( input.boneweight1 ) / 255.0f ) *  BoneMatrices[ input.boneindex1 ];
	bonematrix += ( float( input.boneweight2 ) / 255.0f ) *  BoneMatrices[ input.boneindex2 ];
	bonematrix += ( float( input.boneweight3 ) / 255.0f ) *  BoneMatrices[ input.boneindex3 ];

	// World matrix from instance buffer
	matrix worldMatrixInstance = InstanceLocations[ InstanceID ];

	// Transform via combined bones + world matrix
	output.position = mul(input.position, bonematrix);
	output.position = mul(output.position, worldMatrixInstance );
	
	// Animate normal the same way
	output.normal = mul(input.normal, bonematrix);
	output.normal = mul(output.normal, worldMatrixInstance );

	// Camera view
        output.position = mul(output.position, viewMatrix);
	float4 cameraPosition = output.position;

	// vertex color
	output.vertex_color = input.vertex_color;

	// billboard?
	if( flags & PER_MESH_FLAG_BILLBOARD )
	{
		matrix boneWorldMat = mul( bonematrix, worldMatrixInstance );
		matrix boneWorldViewMat = mul( boneWorldMat, viewMatrix );
		//output.position = input.position + float4( boneWorldMat._41, boneWorldMat._42, boneWorldMat._43, 1.0f );
		output.position = input.position + float4( boneWorldViewMat._41, boneWorldViewMat._42, boneWorldViewMat._43, 1.0f );
		//output.position = input.position + float4( viewMatrix._41, viewMatrix._42, viewMatrix._43, 1.0f );
	}
		
	output.position = mul(output.position, projectionMatrix);
	 
	output.tex = input.tex;

	// Fog calc
	output.fogFactor = saturate((fogEnd - cameraPosition.z) / (fogEnd - fogStart));

	output.instance = InstanceID;
    
        return output;
}

I am using a y-up system, if it matters.

 

Please note there are no issues with the shader outside of the billboarding so please no recommendations on other things I can do differently.  I just want to know how to billboard within the context of what you see here.

 

Thanks..

Edited by relaxok

Share this post


Link to post
Share on other sites
Advertisement

Out.Pos = mul(float4(J + mul(Wm,Vm)[3], 1.0f), Pm);

 

float4 Out.Pos - result

float3 J - triangle in object space what must to bee bilboarded

float4x4 Wm - object to world space matrix

float4x4 Vm - world to view space matrix

float4x4 Pm - view to screen space matrix

 

And this tringle will always be aligned to screen

 

But triangel must be aligned to screen.

Screen coordinates is:

X wide

Y heght

Z deep

 

----------------------------

| Y                             |

| ^                              |

| |                               |
| | Z                            |

| |------------> X           |

----------------------------

 

Culling may to make your triangle invizible

Edited by 8up tuotlo

Share this post


Link to post
Share on other sites

Out.Pos = mul(float4(J + mul(Wm,Vm)[3], 1.0f), Pm);

 

float4 Out.Pos - result

float3 J - triangle in object space what must to bee bilboarded

float4x4 Wm - object to world space matrix

float4x4 Vm - world to view space matrix

float4x4 Pm - view to screen space matrix

 

And this tringle will always be aligned to screen

 

But triangel must be aligned to screen.

Screen coordinates is:

X wide

Y heght

Z deep

 

----------------------------

| Y                             |

| ^                              |

| |                               |
| | Z                            |

| |------------> X           |

----------------------------

 

Culling may to make your triangle invizible

 

It seems like that's what I'm doing?

 

Latest attempt:

// billboard?
	if( flags & PER_MESH_FLAG_BILLBOARD )
	{
		matrix boneWorldMatrix = mul( bonematrix, worldMatrixInstance );
		matrix boneWorldViewMatrix = mul( boneWorldMatrix, viewMatrix );
		
		float3 position = input.position + float3( boneWorldViewMatrix._41, boneWorldViewMatrix._42, boneWorldViewMatrix._43 );
		output.position = mul( float4( position, 1.0f ), projectionMatrix );
	}
	else
	{	
		output.position = mul(output.position, projectionMatrix);
	}

Share this post


Link to post
Share on other sites

Yes, it is.

BUT your triangle must already be placed in CMERA coordinates in vertex buffer(your mesh).

it means thad what up side of your triangle is y+;

front side z+( or z-) i forget ( try two variants; 

and right side is x+;

 

THAN THIS works so

 

if( flags & PER_MESH_FLAG_BILLBOARD )
    {
        matrix boneWorldMatrix = mul( bonematrix, worldMatrixInstance );    
        matrix boneWorldViewMatrix = mul( boneWorldMatrix, viewMatrix );  
        
        float3 position
= input.position + float3( boneWorldViewMatrix._41, boneWorldViewMatrix._42, boneWorldViewMatrix._43 );

        now we TRANSLATE our triangle from Object space to World space ONLY translate no rotations (and this is the bilboarding)
        output.position = mul( float4( position, 1.0f ), projectionMatrix ); standart projection

    }
    else
    {    
        output
.position = mul(output.position, projectionMatrix);
    }    

 

we do NOT make rotations

thet means thad what if our triangle were ben rotatet from the CMERA we do not see it

screen tays on z+ (or z-) and takes look an another side (this is CMERA SPACE)

 

Wm takes our verties from ObjectSpce to WorldSpace

Vm takes our vertices from WorldSpace to ViewSpace - transfer vertices without rotation its (BILLBOARDING) but triangle must be already placed correctly

Pm takes our vertices from ViewSpace to ScreenSpace

Share this post


Link to post
Share on other sites

        now we TRANSLATE our triangle from Object space to World space ONLY translate no rotations (and this is the bilboarding)

 

 

Isn't the line:

 

float3 position = input.position + float3( boneWorldViewMatrix._41, boneWorldViewMatrix._42, boneWorldViewMatrix._43 );

 

supposed to do exactly that?  adjust by the translation only..

Share this post


Link to post
Share on other sites

To billboard an object you are supposed to multiply it by the camera matrix, not the view matrix.  The view matrix is the inverse of the camera matrix and it is what you send in an MVP (model-view-projection) matrix.

You should not be manually adjusting positions etc.  It’s nothing more than a single matrix multiply.

 

 

L. Spiro

Share this post


Link to post
Share on other sites

To billboard an object you are supposed to multiply it by the camera matrix, not the view matrix.  The view matrix is the inverse of the camera matrix and it is what you send in an MVP (model-view-projection) matrix.

You should not be manually adjusting positions etc.  It’s nothing more than a single matrix multiply.

 

Why would that accomplish not rotating it?

Share this post


Link to post
Share on other sites

My new idea was to try making a billboarding view matrix which does the translation based on the real camera rotations, but for the rotation part of the view matrix, uses the inverse matrices.

 

This results in ALMOST the correct result.. the mesh now stays 'camera facing' no matter what the camera is doing, however the translation seems to put it all over the place.  I'm wondering how this can be when the translation is the same as when not billboarding:

 

http://bh.polpo.org/quad_no_rot1.avi

 

What adjustment can I make to keep the translation correct?

void CCamera::transform( float x, float y, float z, float fOrientation )
{
	XMMATRIX matRotationX = XMMatrixRotationX( m_Pitch );
	XMMATRIX matRotationY = XMMatrixRotationY( XMConvertToRadians( fOrientation  * 360.0f ) + m_Yaw );
	XMVECTOR unitVec = XMVectorSet( 0.0f, m_Height, -m_Distance, 0.0f );
	XMVECTOR transVec = XMVector3TransformCoord( unitVec, matRotationX * matRotationY );

	m_posX = x + XMVectorGetX( transVec );
	m_posY = y + XMVectorGetY( transVec );
	m_posZ = z + XMVectorGetZ( transVec );

	XMMATRIX matTranslation = XMMatrixTranslation( m_posX, m_posY, m_posZ );
	XMVECTOR matInvDeter;
	XMMATRIX matInverse = XMMatrixInverse( &matInvDeter, matRotationX * matRotationY );
	XMMATRIX matTransInverse = XMMatrixInverse( &matInvDeter, matTranslation );

	// Billboard version
	XMVECTOR matRotBillboardDeter;
	XMMATRIX matRotationXBillboard = XMMatrixInverse( &matRotBillboardDeter, matRotationX );
	XMMATRIX matRotationYBillboard = XMMatrixInverse( &matRotBillboardDeter, matRotationY );
	XMMATRIX matInverseBillboard = XMMatrixInverse( &matInvDeterBillboard, matRotationXBillboard * matRotationYBillboard );
	
	XMStoreFloat4x4( &m_matView, matTransInverse * matInverse );
	XMStoreFloat4x4( &m_matBillboard, matTransInverse * matInverseBillboard );
	XMStoreFloat4x4( &m_matRotationX, matRotationX );
	XMStoreFloat4x4( &m_matRotationY, matRotationY );
	XMStoreFloat4x4( &m_matTranslation, matTranslation );

	calculateViewFrustum();
}
Edited by relaxok

Share this post


Link to post
Share on other sites

Why would that accomplish not rotating it?

Because it undoes the rotation applied by the camera…

 

My new idea was to try making a billboarding view matrix which does the translation based on the real camera rotations, but for the rotation part of the view matrix, uses the inverse matrices.

Why don’t you just quickly make the WBP (world-billboard-projection) matrix and be done with all that ridiculous math?
 
XMMATRIX mBillboard;
XMMatrixInverse( &mBillboard, m_matView ); // m_matView is the inverse of another matrix, so instead of inverting it again you could just copy that matrix.
// Only keep the upper-left 3×3.
mBillboard._41 = mBillboard._42 = mBillboard._43 = 0.0f;  // Billboard matrix complete.


XMMATRIX mBillboardView = mBillboard * m_matView; // Can be used instead of the view matrix.
XMMATRIX mBillboardViewProjection = mBillboardView * m_matProj; // Can be used instead of the view-projection matrix.
Why make it so complicated?


L. Spiro Edited by L. Spiro

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

GameDev.net is your game development community. Create an account for your GameDev Portfolio and participate in the largest developer community in the games industry.

Sign me up!