HOQ say hello to HZB

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For my leisurely weekend, I decided to tackle the problem of Occlusion once and for all, and to that end spent the first six hours reading every technique every used in computer games from CPU software rendering through to insanely ambitious prediction systems for reducing hardware query checks. The reason I am not satisfied with the current hardware query system in Reloaded is that the object 'popping' you see when you run around corners is not just 'occasional' but pretty much in your face!  No-one has come up with a decent solution to solve the occlusion query popping as it is an inevitable result of having the data for the occlusion cull one frame behind the rest of the visual rendering. Only coherence systems attempt to solve this, but it only amounts to guesswork. I even pioneered some non-white-paper thoughts about creating multiple queries as a product of the player running in several dead-reckoning vectors, but I quickly realized the cost of those queries would be insane, and there are a lot of articles out there which feverishly attempt to reduce query count so why would I deliberate make multiples of them!  Here are my brain storming notes from the day:

During my researches, I stumbled onto a technique called Hierarchical Z Buffers (used in several top end games you know) which basically renders a smaller version of the scene into a depth buffer and squashes it down into a real-time mipmap. It is then used in concert with any object you wish to test the occlusion state of using some pretty wicked GPU based test. The wicked part is how they get the DX9 test data back into system memory ;)

I did not wish to go this route originally as adding another pre-render to the scene seemed like spending more GPU time than saving it.  It's now nearly 3AM and I want to eat and watch a movie before I sleep, and I am currently at the point where most of the C++ code is in a new set of DBP commands and I just need to establish some occluder candidates, create an object bounds database and then set the object visibility flags.  These last three steps should allow me to choose key occluders from any Reloaded scene, then sit back and watch as the GPU performs full occlusion testing with a single draw call and instantly rejects thousands of arbitrary objects from the scene :)  I will know more come Monday afternoon, but the early results are exciting!

I have recently discovered how to use Microsoft PIX properly (now replaced with the VS graphical debugger) and have been having a whale of a time watching the scene built up one draw call at a time. I plan to use this tool A LOT now I know where all the buttons are. For those who just fell over in shock, I do admit that I was one of those coders who mostly 'guessed' where the rendering problems where in my engine. The upshot of course is that these days my guesses are pretty accurate!