internal void BeginBillboards()
{
// Make sure we aren't calling this more than once
Debug.Assert( this.lockPtr == IntPtr.Zero );
/* NOTE: most engines generate world coordinates for the billboards
directly, taking the world axes of the camera as offsets to the
center points. I take a different approach, reverse-transforming
the camera world axes into local billboard space.
Why?
Well, it's actually more efficient this way, because I only have to
reverse-transform using the billboardset world matrix (inverse)
once, from then on it's simple additions (assuming identically
sized billboards). If I transformed every billboard center by it's
world transform, that's a matrix multiplication per billboard
instead.
I leave the final transform to the render pipeline since that can
use hardware TnL if it is available.
*/
// create vertex and index buffers if they haven't already been
if ( !this.buffersCreated )
{
this.CreateBuffers();
}
// Only calculate vertex offets et al if we're not point rendering
if ( !this.pointRendering )
{
// Get offsets for origin type
this.GetParametricOffsets( out this.leftOff, out this.rightOff, out this.topOff, out this.bottomOff );
// Generate axes etc up-front if not oriented per-billboard
if ( this.billboardType != BillboardType.OrientedSelf &&
this.billboardType != BillboardType.PerpendicularSelf &&
!( this.accurateFacing && this.billboardType != BillboardType.PerpendicularCommon ) )
{
this.GenerateBillboardAxes( ref this.camX, ref this.camY );
/* If all billboards are the same size we can precalculate the
offsets and just use '+' instead of '*' for each billboard,
and it should be faster.
*/
this.GenerateVertexOffsets( this.leftOff,
this.rightOff,
this.topOff,
this.bottomOff,
this.defaultParticleWidth,
this.defaultParticleHeight,
ref this.camX,
ref this.camY,
this.vOffset );
}
}
// Init num visible
this.numVisibleBillboards = 0;
// Lock the buffer
this.lockPtr = this.mainBuffer.Lock( BufferLocking.Discard );
this.ptrOffset = 0;
}
