caius howcroft - Developer IT

Quadtree collapsing

- by Caius Eugene

Okay so i've spent a few days learning what a quadtree is and how to implement one. So far I have a quadtree that when I click inside a leaf it subdivides, I wondering how do I get the previous subdivisions to collapse back up, so that only one area is subdivided at a time? This is what mine looks like: (1. initial mouse click) (2. another mouse click) The aim to to eventually track the position of my mouse and subdivide the area it is in dynamically. THE OVERALL aim it to use this to create a terrain mesh and subdivide based on the camera. But I've gone right back to basics to get an understanding of how this will work. Any advice would be grand! - Caius

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Calculating adjacent quads on a quad sphere

- by Caius Eugene

I've been experimenting with generating a quad sphere. This sphere subdivides into a quadtree structure. Eventually I'm going to be applying some simplex noise to the vertices of each face to create a terrain like surface. To solve the issue of cracks I want to be able to apply a geomitmap technique of triangle fanning on the edges of each quad, but in order to know the subdivision level of the adjacent quads I need to identify which quads are adjacent to each other. Does anyone know any approaches to computing and storing these adjacent quads for quick lookup? Also It's important that I know which direction they are in so I can easily adjust the correct edge.

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Demystifying "chunked level of detail"

- by Caius Eugene

Just recently trying to make sense of implementing a chunked level of detail system in Unity. I'm going to be generating four mesh planes, each with a height map but I guess that isn't too important at the moment. I have a lot of questions after reading up about this technique, I hope this isn't too much to ask all in one go, but I would be extremely grateful for someone to help me make sense of this technique. 1 : I can't understand at which point down the Chunked LOD pipeline that the mesh gets split into chunks. Is this during the initial mesh generation, or is there a separate algorithm which does this. 2 : I understand that a Quadtree data structure is used to store the Chunked LOD data, I think i'm missing the point a bit, but Is the quadtree storing vertex and triangles data for each subdivision level? 3a : How is the camera distance usually calculated. When reading up about quadtree's, Axis-aligned bounding box's are mentioned a lot. In this case would each chunk have a collision bounding box to detect the camera or player is nearby? or is there a better way of doing this? (raycast maybe?) 3b : Do the chunks calculate the camera distance themselves? 4 : Does each chunk have the same "resolution". for example at top level the mesh will be 32x32, will each subdivided node also be 32x32. Example below:

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Bending of track in a racing game

- by caius

I am trying to create a small racing game in which the track would be modeled using a BSpline curve for the path's center line and directional vectors to define the 'bending' of the track at each point. My problem is that I don't know how to calculate the correct bending / slope of the curve, in such a way that it would be optimal or at least visually nice for a car to 'bend in the corner'. My idea was to use the direction of the 2nd derivatives of the curve, however while this approach looks fine for most of the track, there are points in which the 2nd derivative makes sharp 'twists' / very quick 180 degree flips. I also read about 'knots' of bsplines, but I don't know if such 'twist' in 2nd derivatives is a knot or knots are something else. Can you tell me that using a BSpline: 1. How could I calculate a visually nice bending of a track for a racing game? 2. Is it possible to do this by using some simple calculations of centripertal force / gravity? 3. Is it possible to do this by using 1st, 2nd and 3rd derivatives of the BSpline curve? I am not looking for the 'physically correct' bending angle for the track, I would just like to create something which is visually pleasing in a simple game. I am using a framework which has a built-in class for BSpline, including support for 1st, 2nd and 3rd derivatives of the curve.

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Tracking costs within one AWS account

- by caius howcroft

I have what I'm sure is a very common problem. Our company has many projects and groups working for different clients. We do a lot of our development work in the cloud and deploy our solutions there. We have a VPC set up that isolates projects from each other in their own subnet and that VPC is getting a hardware VPN connection back to HQ. We need to keep track of the cost run up by every project. The way I currently implement this is by providing my own tools for starting and stopping instances which log which user (and thus which project) to bill the instance too. This works okay for BoxUsage costs but not for other costs. I could create a separate account for each project and use consolidated billing, this I think would allow me to pay once but track costs per "project", but I would then not be able to share common resources (like bring account B's running instances inside the same VPC). Does anyone have any suggestions? Cheers C

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How can I use alerts like the volume alert in the iPhone in my apps?

- by guydor

Hi, What is the kind of alerts like the iPhone volume See picture: http://caius.name/images/ringer.jpg Thanks,

Developer IT