Billboarding

Billboarding is a technique that orients a object (usually a texture-mapped quadrilateral) such that it is always perpendicular to the camera regardless of how the camera is transformed. It can for example be used to display complex geometries at a distance when detail is not required.

There are at least two methods to achieve this effect, this program implements one "cheap" and one "true" method as described by Lighthouse 3D. However, the methods have been modified by me to use quaternions instead and without the fixed OpenGL pipeline.

The cheap method is easy and fast to implement but never modifies the object orientation state, only during render is the technique put in place. It works by replacing the rotation section in the model-view matrix with the identity matrix. Because the matrix is in view space, the identity matrix will keep the objects front direction towards the camera. If scaling is desired the rotation must be replaced with the scale values of the sprite.

The true method is a bit more involved since it actually modifies the object orientation state while also being a bit more expensive relative to the cheap method. It works by simply reorienting the object in world space to look at the cameras current position in world space without rolling unless moving right above it.

Note that the billboarding effect from each method is different, the cheap method gives the illusion of following both the camera position and its orientation while the true method gives the illusion to only follow the camera position.

Having the object facing the camera on all rotation axes is not always desired. The program features two effects, "spherical" which rotates the sprites about all axes and "cylindrical" which only rotates about the y-axis.

The cheap method can be easily implemented in the vertex shader as described by Geeks 3D.

• Press F1 to toggle billboarding.
• Press F2 to toggle between spherical and cylindrical billboarding.
• Press F3 to toggle between cheap and true method.
• Press w, a, d, s to fly forward, left, right or back.
• Press r, q to fly up and down.

Screenshot

How-to

This project depends on Gust, see its project page for details on dependencies.

Recursive clone required

$ git clone --recursive <repository>

Build and run

$ scons
$ cd bin
$ ./billboarding

Cleanup

$ scons -c

References

1. Simple Billboarding Vertex Shader (GLSL). [downloaded 2014-08-17]. Available from http://www.geeks3d.com/20140807/billboarding-vertex-shader-glsl/.
2. Billboarding Tutorial. [downloaded 2014-08-17]. Available from http://www.lighthouse3d.com/opengl/billboarding/index.php3?billInt.