AddSpriteToBillboard
Introduction
To "billboard" a Sprite means to adjust its rotation so that it is always facing the Camera. Billboarded sprites are only needed for games with a 3D camera. Note that billboarded sprites typically not used for UI because UI and HUD should be handled by Gum.
Games like Doom used a billboard effect on enemies and items. Mario 64 also used a billboard effect on its trees. This effect is evident when running around billboarded Sprites.
The AddSpriteToBillboard tells the calling Camera to hold a reference to the argument Sprite and adjust its rotation every frame so that it faces the Camera.
Usage
Billboarding and Rotation
Billboarding is implemented by modifying the argument Sprite's Rotation values. Therefore, a billboarded Sprite cannot be rotated on its X or Y axes. In other words, billboarding overwrites RotationX and RotationY values. Changing any rotation or rotation velocity values on the X or Y will not have any impact on billboarded Sprites. Billboarded Sprites can still be rotated on the Z axis.
Billboarding and Attachment
Both billboarding and attachments modify the rotation of PositionedObjects. To resolve this conflict, you are responsible for deciding which should take precedence. If you'd like the attachment to be dominant, you should not make a Sprite billboarded. If, on the other hand, you still want your Sprite to be billboarded, but it should have an attachment, set the ParentRotationChangesRotation property to false. For more information, see the ParentRotationChangesRotation article.
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