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# DAVco

Member Since 22 Jan 2011
Offline Last Active Nov 05 2012 11:23 AM

### Extracting Frustum Planes (Hartmann & Gribbs method)

10 October 2012 - 08:55 AM

Hello, I have been grappling with the Hartmann/Gribbs method of extracting the Frustum planes for some time now, with little success. There doesn't appear to be a "definitive" topic or tutorial which combines all the necessary information, so perhaps this can be it

First of all, I am attempting to do this in C# (For Playstation Mobile), using OpenGL style Column-Major matrices in a Right-Handed coordinate system but obviously the math will work in any language.

My projection matrix has a Near plane at 1.0, Far plane at 1000, FOV of 45.0 and Aspect of 1.7647.

I want to get my planes in World-Space, so I build my frustum from the View-Projection Matrix (that's projectionMatrix * viewMatrix). The view Matrix is the inverse of the camera's World-Transform.

The problem is; regardless of what I tweak, I can't seem to get a correct frustum. I think that I may be missing something obvious.

Focusing on the Near and Far planes for the moment (since they have the most obvious normals when correct), when my camera is positioned looking down the negative z-axis, I get two planes facing in the same direction, rather than opposite directions. If i strafe my camera left and right (while still looking along the z axis) the x value of the normal vector changes.

Obviously, something is fundamentally wrong here; I just can't figure out what - maybe someone here can?

### Strategic Zoom

02 May 2012 - 05:21 AM

I've recently been trying to dig up any technical information on how exactly the "Strategic Zoom" is implemented in Supreme Commander.

I'm guessing that the game uses a layer-of-detail system with a large amount of different layers, but one developer quote I keep encountering is "it would be very hard to implement this in [Other game] because they haven't designed it from the ground up with that in mind."

Scaling the terrain effectively would be the biggest challenge, I think. Even at the farthest zoom level, the map still looks intricately detailed. This thread mentions that the maps in SUPCOM use Megatexturing.

Does anyone have any thoughts on this? Cheers

### OpenGL VBO and/or Vertex Arrays

22 January 2011 - 09:13 AM

I'm having trouble sorting out the difference between Vertex Arrays and Vertex Buffer Objects in OpenGL. Tutorials on the web seem to use the terms interchangeably, which I think is incorrect?

I have some notes from my programming class that state "[A VBO] is an array of (possibly interleaved) vertex attributes....can be stored in video memory." The notes also say that "[Vertex Array Objects] Despite the name, do not store vertices. Used to store OpenGL state attributes. May contain a reference pointer to a VBO."

As far as I understand, a VBO holds geometry data (Vertex coordinates, Texture coordinates, Vertex colour, Material, etc) and may be stored on the graphics hardware, rather than in main memory. So my question is, what is the function of a Vertex Array Object?