The BillboardRenderer is a scene node renderer which handles BillboardNodes and ParticleSystemNodes.

Particle systems need to have certain particle parameters for rendering. If a required particle parameter is missing, the particle system is ignored by the renderer! See ParticleSystemNode for more information.

Buffer Size: The renderer batches billboards and particles using an internal buffer. The property BufferSize limits the number of billboards/particles that can be drawn with a single draw call.

Render States: The BillboardRenderer changes the following render states of the graphics device.

• The appropriate BlendState is set depending on the type of billboards/particles.
• Culling is disabled in the RasterizerState. Billboards/particles are rendered "two-sided".

• When using HiDef profile with soft particles the DepthStencilState is set to None (= depth-reads and depth-writes are disabled).

  When using Reach profile or HiDef profile (without soft particles) the DepthStencilState is not changed. The DepthStencilState should be set explicitly before rendering billboards/particles. In most cases depth-writes should be disabled, for example:

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  graphicsDevice.DepthStencilState = DepthStencilState.DepthRead;
  billboardRenderer.Render(nodes, context);

Soft Particles (require HiDef profile):
Billboards and particles are usually rendered as flat quads, which cause hard edges when they intersect with other geometry in the scene. "Soft particles" are rendered by performing an explicit depth test in the pixel shader. Soft particles fade out near the camera and create smooth transitions when they intersect with other geometry.

To enable rendering of soft particles set the property EnableSoftParticles to . In addition the depth buffer needs to be set in the render context (property GBuffer0).

For image billboards: The Softness property defines whether billboards are rendered "hard" or "soft".

For particle systems: The Softness parameter (a uniform particle parameter of type Single) defines whether particles are rendered "hard" or "soft".

High-Speed, Off-Screen Particles (require HiDef profile):
Large amounts of particles covering the screen can cause a lot of overdraw. This can reduce the frame rate, if the game is limited by the GPU's fill rate. One solution to this problem is to render particles into a low-resolution off-screen buffer. This reduces the amount of overdraw, at the expense of additional image processing overhead and image quality.

To enable off-screen rendering set the property EnableOffscreenRendering to . In addition a low-resolution copy of the depth buffer (half width and height) needs to be stored in renderContext.Data[RenderContextKey.DepthBufferHalf].

In XNA off-screen rendering clears the current back buffer. If necessary the renderer will automatically rebuild the back buffer including the depth buffer. For the rebuild step it will use the same parameters (e.g. near and far bias) as the current RebuildZBufferRenderer stored in renderContext.Data[RenderContextKey.RebuildZBufferRenderer].

Caution
When off-screen rendering is enabled the BillboardRenderer automatically switches render targets and invalidates the current depth-stencil buffer.

Reference