# Unity 3D: A rough and ready computation of normals - useful for procedural meshes

Here is a rough and ready method to compute a meshes' vertex normals knowing the vertices and the indicies of your mesh.

`  List[] normalBuffer= new List[NumVerts];    for(int vl = 0; vl < normalBuffer.Length; ++vl) {     normalBuffer[vl] = new List();  }    for( int i = 0; i < NumIndices; i += 3 )  {    // get the three vertices that make the faces    Vector3 p1 = m_original[m_mesh.triangles[i+0]];    Vector3 p2 = m_original[m_mesh.triangles[i+1]];    Vector3 p3 = m_original[m_mesh.triangles[i+2]];    Vector3 v1 = p2 - p1;    Vector3 v2 = p3 - p1;    Vector3 normal = Vector3.Cross(v1, v2 );    normal.Normalize();    // Store the face's normal for each of the vertices that make up the face.    normalBuffer[m_mesh.triangles[i+0]].Add(normal);    normalBuffer[m_mesh.triangles[i+1]].Add(normal);    normalBuffer[m_mesh.triangles[i+2]].Add(normal);  }  for( int i = 0; i < NumVerts; ++i )  {   for (int j = 0; j < normalBuffer[i].Count; ++j) {    m_normals[i] += normalBuffer[i][j];   }       m_normals[i]  /= normalBuffer[i].Count;  }`

# Unity 3D Immediate Mode: What's the trick with GL.modelview?

Unity 3D's immediate mode is really useful for debugging or adding a bit of chrome to a scene. While it's not the most efficient way of getting something on the screen it's so quick and handy. For those not using Unity 3D Pro. The GL namespace and functionality isn't available to you.

Here's a little tip for setting the GL.modelview matrix so you can pump local space vertices into you GL.Vertex calls and have everything appear in the right spot.

For example if I want to draw a line using model local space I need to setup the modelview matrix so GL primitives appear in the place in our 3D world.

First of all we grab the scene camera using for example (using the C# API) :

`GameObject camera = GameObject.Find("Main Camera");`

Next we need to compose a matrix that will take into account the scene camera's position and the position of the model we're using. The final trick of composing this matrix is to convert from a Left handed co-ordinate system to a right handed co-ordinate system.

Unity 3D normally uses a Left Handed camera co-ordinate system, where Z is postive leading out of the front of the camera. The underlying rendering system (originally designed on the Macintosh andOpenGL) is a Right Handed System (where Z is negative out of the Camera). The GL.modelview is expected to be in Right Handed.

So to composite the correct modelview matrix we're going to first create a matrix to transform from a left handed to right handed system. We could do:

`Matrix4x4 mat = Matrix4x4.identity;mat[2,2] *= -1.0f;`

Now we're ready to go, if we have the camera transform, the model tranforms and our conversion matrix. The result looks like this:

`GL.modelview = mat * (camera.transform.worldToLocalMatrix  * transform.localToWorldMatrix);`

Now you can issue GL.Vertex3 commands in model local space

# Schedule Steam (and use your Offpeak bandwidth)

Antipodeans get a raw deal when it comes to the Internet. It's expensive and slow, not to mention it's become a political hot potatoe with several poorly thought out schemes relating to the internet being pushed through in Canberra.

Politics aside for now, that's not the reason for this post.

With the core market for Valve's Steam service no doubt being the American market little attention was paid to download manager style features such as bandwidth throttling and scheduling. Valve's bandwidth heavy Cornocopia of Software can chew through the average Australian/NZ household's monthly bandwidth allocation in hours.

Most Australian bandwidth plans have a Peak and Offpeak timesplit. Peak obviously falls into all those times you're likely to use the Internet. Unless you're a serious nightowl, at month's end you've probably still got a considerable amount of your Offpeak bandwidth allocation remaining.

Steam doesn't offer built in download scheduling so here is a short recipe on how you can coax Stream to schedule a download for the Offpeak internet hours.

I'm using Windows XP in this example, I can only assume it's similar for Vista and Windows 7.

Firstly on the Login screen of Steam make sure you have the "remember password" option checked. You'll need to do this to allow Steam to automatically login and resume or initiate a download.

Login in to steam initially, and go to the "My Games" tab and right click to "Install game..." on an undownloaded title you'd like to download and install. Steam will present you with details about the install, click next proceed. It will the process the file cache, and then ask you if you wish to create a shortcut to the desktop, which you should check (this is needed for later). The download will begin.

Now that you've compleated the manual steps to setup the download, you can exit Stream. Once it's shutdown we can schedule the download for Offpeak hours.

Go to your Desktop and find the shortcut you chose to create from Steam in the previous step. Right click on the shortcut and choose properties. You'll be presented with the shortcut properties. On this screen there will be a textbox labelled "Target". Highlight all the text in this textbox and copy it to your pasteboard. In this example the text I copied is (It's Half Life 2: Deathmatch):

`"c:\Program Files\Steam\steam.exe\" -applaunch 240`

Next choose Start->Run from the Main OS Menu, and type "cmd" in into the textbox presented in order to open a command window.

In the example below I've scheduled Steam to begin downloading at 2:00 AM in the morning. This is a typical Offpeak time, but you're might be different so you might want to check.

Now we can construct the command line:

`schtasks /Create /TR "\"C:\Program Files\Steam\steam.exe\" -applaunch 240" /ST 02:00:00 /SC ONCE /TN Steam`

I've used the text I copied from the desktop shortcut as you can see. Pay special notice to the "\" characters I've inserted before the quotes. These are required to be able to input the whole command properly.