• FEATURED

View more

View more

View more

### Image of the Day Submit

IOTD | Top Screenshots

### The latest, straight to your Inbox.

Subscribe to GameDev.net Direct to receive the latest updates and exclusive content.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

2 replies to this topic

### #1Juliean  Members

Posted 13 May 2014 - 11:19 AM

Hello,

is it possible to rotate a camera-oriented billboard that is created in a geometry-shader around the look-axis by a certain angle, given that the angle input is only a floating value, not an entire rotation matrix? I'm using this for a particle-cloud-renderer. This is the shader-body I'm using, its written in my own shader language, the code uses HLSL-instrincts though, so I hope everbody is able to understand it (the geometryShader-main is the interesting part though):

 vertexShader
{
in
{
float vPosition;
float3 vTranslation;
float scale;
float rotation;
float type;
}

out
{
float4 vPosition;
float scale;
float rotation;
float type;
}

main
{
out.vPosition.xyz = in.vTranslation;
out.scale = in.scale;
out.rotation = in.rotation;
out.type = in.type;
}
}

{
input Stage
{
matrix mViewProj;
float3 vCameraPos;
float3 vCameraUp;
}

out
{
float4 vPosition;
float2 vTexture;
}

primitives
{
in: point[1];
out: triangle[4];
}

main
{
// choose texture from atlas
float2 vIndex = float2(fmod(in[0].type, 4.0f), floor(in[0].type / 4.0f));
float2 texCoord[4];
float texSize = 0.25f;
float4 vTexCoords = float4(vIndex.x * texSize, vIndex.y * texSize, (vIndex.x + 1) * texSize, (vIndex.y + 1) * texSize);
texCoord[0] = float2(vTexCoords.x, vTexCoords.w);
texCoord[1] = float2(vTexCoords.z, vTexCoords.w);
texCoord[2] = float2(vTexCoords.x, vTexCoords.y);
texCoord[3] = float2(vTexCoords.z, vTexCoords.y);

// create orientation vectors
float3 vPlaneNormal = normalize(in[0].vPosition.xyz - vCameraPos);
float3 vRight = normalize(cross(vPlaneNormal, vCameraUp));
float3 vUp = normalize(cross(vRight, vPlaneNormal));

vRight *= in[0].scale;
vRight *= 0.5f;

vUp *= in[0].scale;
vUp *= 0.5f;

// TODO: use in[0].angle to rotate the quad around vPlaneNormal

// setup vertices
float3 vVerts[4];
vVerts[0] = in[0].vPosition.xyz - vRight - vUp; // Get bottom left vertex
vVerts[1] = in[0].vPosition.xyz + vRight - vUp; // Get bottom right vertex
vVerts[2] = in[0].vPosition.xyz - vRight + vUp; // Get top left vertex
vVerts[3] = in[0].vPosition.xyz + vRight + vUp; // Get top right vertex

for(int i = 0; i < 4; i++)
{
out.vPosition = mul(float4(vVerts[i], 1.0f), mViewProj);

out.vTexture = texCoord[i];
Append();
}
}
}


I figured that I could use trigonometric functions to add a certain amount of the right and up-vector to achieve the rotation, however I'm kind of stuck in the execution. Can somebody help me on this? Any drawing, explanation, or preferably pseudo-code would be quite nice.

Edited by Juliean, 13 May 2014 - 11:20 AM.

### #2unbird  Members

Posted 13 May 2014 - 12:13 PM

vRight and vUp are orthogonal and of the same length, so you can use the 2D rotation, locally that is:

float s, c;
sincos(in[0].rotation, s, c);
float3 vUpNew    = c * vRight - s * vUp;
float3 vRightNew = s * vRight + c * vUp;

Use these new values for the subsequent point expansion.

PS: Haven't checked this, but that should be the gist of it.

PPS: Small check. Not actually billboards, but the rotation works.

### #3Juliean  Members

Posted 13 May 2014 - 01:52 PM

Works like a charm, thanks!

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.