Conclusion

Pros and Cons

There are many pros and cons to the occlusion culling interpretation presented. It is very easy to implement, and it is very accurate and flexible. For example, objects behind a pane of glass can be culled appropriately (this can be achieved by making the glass object's bounding mesh an outline of the glass). Also, the level of accuracy and speed of the algorithm can be altered easily by changing the bounding meshes that are used. More vertices means more accurate and slower; less vertices means less accurate and faster.

However, there are numerous faults in this method. For one, it renders every object up to 3 times (twice during the culling operation, and possibly again during the primary render). This slows the cull down tremendously. Also, it requires a DirectX 9 compliant graphics card.

Possible Optimizations

• If frustum culling were to be implemented, the sectors and objects outside of the view volume could be thrown out from the start.
• The size of the occlusion texture and surface could be decreased, although smaller sizes tend to decrease the accuracy of the occlusion culling.

The Demo

Included is a fully working demo (with source code) that implements the method discussed. It renders a small forest of 300 randomly placed trees, totaling over 100,000 vertices. The demo requires a DirectX9 compliant card to run. The controls are as follows:

• WASD: Slide camera
• IJKL: Rotate camera
• M: Save bitmap of occlusion surface (saves to buffer.bmp)

Diagram 5.1: Demo screenshot

Final Thoughts

Well, thank-you for checking out my implementation of occlusion culling. I hope that you gained some knowledge from it. I welcome any ideas, suggestions, or corrections.

Dustin Franklin
dustinhimer@comcast.net

Dustin Franklin (aka circlesoft) is a high school student in Mount Joy, Pennsylvania. You can feel free to email him at dustinhimer@comcast.net or contact him through MSN (at that address) or AIM (dutsin2323).