ScreenSpaceDecalExample

Screen Space Decal Example [SSD]

This projects adds a screen space projected decal system which uses a custom entity processor to read the DecalComponent to feed a RenderMesh with our custom shader material to be consumed by the standard rendering system. This is a hacky solution as it relies on copying the existing rendering system's data format.

The decal entity uses a 1x1x1 box as a projector to render the selected texture onto whatever is inside the projector's 'box'. You can adjust the box size by changing TransformComponent.Scale of the decal entity.

Current limitations (however someone smart may be able to implement/extend/fix):

• This is only useful for static entities (eg. ground), and will not work well with skinned (animatable) models.
• Only a texture is rendered, no normal map.
• Since the projection is 'downwards' (relative to the box), the decal will stretch along a 'wall' (as seen in the example scene screenshot below).
• While there is a IsAffectedByShadow property on the decal, changing between the two gives inconsistent lighting.
• There isn't a way to preview the box, which would be useful for debugging purposes.
• Be wary of moving too close to the box, as culling will occur. Depending on your needs, you could possibly just disable culling for the decal.

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Example Scene

This example shows the decal rendering on every RenderGroup except for the ones specified on the Ignore Render Groups mask.

In a real case scenario, you would set the Ignore Render Groups to whatever Render Group(s) the dynamic (animatable) models are set with (and make sure these are not the same Render Groups that you use for static models).

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Currently, a new material object is generated per DecalComponent (ie. per entity). This probably needs to be changed to allow reuse of material instances, however be aware if any of the DecalComponent's field changes at run-time this will affect all entities using the same material instance, so would need to check every render frame if it still belongs to the same material and change to a new material if it's not.

Important Game Studio Notes:

• The entity with the DecalComponent is not selectable in the Game Studio scene editor, and must be selected by the entity tree sub-window.
• DecalComponent.IgnoreRenderGroups does not appear to work in the Game Studio scene editor (due to some oddity with how we're passing the ObjectInfo render target texture), however will work correctly at run-time.

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In the future, it may be possible to make the entity selectable in the scene editor. This will require creating a GizmoComponent, which is part of the Xenko.Assets.Presentation library, however referencing this library stops the game project from compiling.

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Graphics Compositor Setup

ObjectInfo render stage:

ObjectInfoSceneRenderer:

Note: Be sure to make the ObjectInfoSceneRenderer is set before the Forward renderer, otherwise the generated texture will not be set in time.

ObjectInfoRenderFeature and ObjectInfoRenderStageSelector:

Note: The Render Group mask in the RenderStageSelector needs to include all entities that are visible in the scene (ie. both the static AND dynamic entities), and exclude the decal's RenderGroup. In our example scene, the main renderable groups are Group0, Group1, Group2, Group3, and the decal is Group10 (this is completely arbitrary).