Point - Circle

Perhaps one of the most fundamental aspects to collision testing is to see if a point in space is within the bounds of a circle or sphere.

This is done by collapsing the line between the centre of the circle and point into a scalar length, and then comparing it with the radius of the circle.

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Here we have 2 positions (Marked by the black dots), the Origin (Centre) of the circle and the Point. If we split the X and Y coordinates we can make a triangle. Pythagoras can then be used to get the Hypotenuse, giving us the length between the 2 points:

² =

² +

²

So:

=

+

Fill in the X and Y Distances:

To get

from

² we have to square root:

We can now compare this

to the

of the circle, If

a collision occurs as the point is inside the circle.

In our example no collision occurs

This same method can be done with a sphere in 3D, we just add Z values in the Pythagoras step

You can increase performance of the distance calculation by negating the square root (Which is expensive), and instead squaring the radius for comparison. BE WARNED: know your limits when doing this, the max value of a square on int32 is about 2,000,000,000 that sounds a lot, but its only 46,340 squared, depending on your scale this could be as little as 460meters before your calculations will no longer work!

Remember the sphere's radius is largest at its origin no matter what direction the ray comes from, which allows the problem to be converted into a 2D point in Circle test.

[display-posts category="collision" posts_per_page="-1" include_date="true" order="ASC" orderby="title"]','Collision Detection 2 - Point Circle

Preface

I started writing these collision tutorials as I have recently learnt some of these techniques, and found many tutorials completely useless at explaining the core concepts to a novice. In this I aim to show you how I got my head around the concepts of collision detection, and response. Instead of providing you with code to blindly copy and paste, I hope this will give you enough information to go on to create your own code, and know how it works.

Stuff you should already know:

Parallel	Perpendicular	Normal

• Most 3D maths problems can be flattened into 2 Dimensional problems, If your stuck, solve it in 2D then move into the 3rd dimension.


• Use a pen and paper to draw problems out.


• Unit or normalised vector (Wikipedia makes it sound way more complicated than it is, just know the X and Y values fall only in the range of -1 to 1.
  Think of this as a percentage of direction, (1,0) will be 100% right 0% up, (-1,-1) will be moving bottom left at 100%.

Next:

This is an extract from my 3rd year dissertation

Using a Vicon optical motion capture suite (which was available for use in my university) I wanted to take motion capture beyond the movies, and implement a fully interactive gaming experience in which the player is the controller, This allows 6 Degrees of freedom for the player to move in, so leaning around corners, ducking, view freedom from your gun and blind firing, are realised and more immersive than a traditional keyboard and mouse setup could ever be.

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The Vicon suite was one of my primary reasons for choosing the University Of Hull, and I am beyond thrilled to be able to use it for my undergraduate dissertation.

The initial specification I drew up over the summer was for the player to wear a Head mounted LCD display, which allows 3D stereoscopic viewing of my virtual environment, attached to the HMD and gun are fiducial markers that enable optical tracking, the player aims with the toy gun (Which is modified with a wireless mouse) to shoot down virtual enemies.

Game engine progress

My game engine has been created from scratch in OpenGL and C++.

It Currently features:

• 3D Stereoscopic rendering


• First person tracking support (for HMD's)


• Paralax Motion Head tracking support (for monitors/projectors)


• GLSL shader support, with bump mapping and per fragment lighting


• Skybox shader


• OBJ model loader and texture support


• Collision detection for the world, AI and gun (Ray-Sphere, AABB, OBB)


• AI enemies which seek out the player avoiding world objects.


• TCP communication with a Vicon motion capture suite


•  Configurable files for tracking data transformations

It has been particular intensive in matrices with converting from the tracking coordinate system to OpenGL's co-ordinate system, I learnt openGL's shader pipeline to enable shaders that I created from my

to work within the engine. Wrote an AI collision avoidance and steering algorithm based on vector maths.

Tools used

Visual Studio C++

FreeGlut

GLSL

Wavefront OBJ

Render Monkey - Shader design

Blender - Gun model design & model cleanup/UV mapping

Google Sketchup - Level design

Sculptris - Charater models

Photoshop - General texturing

Vicon Real time emulator

Screenshots

These screenshots are now outdated (See below!)

Clockwise: Spectator camera view of level, First person View, 'Flyray' flying enemy with bumpmapping

Close up of the players area in which they have to defend

10/03/11 Update

Rooftop level progress (Google Sketchup)

Google sketchup makes an interesting tool for level design, with the use of a 3rd party OBJ explorer the CAD tool could export models directly into my game, The texture mapping and dynamic geometry features of sketchup pretty much sold it to me as my weapon of choice to create my 3D rooftop.

20/03/2011 Update

Level is fully complete, Textures were aquired online, and bump maps were created using Nivida's Normal map plugin for photoshop. The GLM model class was modified to support 2 textures and a bumpmaped phong shader, with a fallback shader if there is no normal map for a texture. Normal maps are defined in the models .mtl file.

30/03/2011 Update

The HMD idea was scrapped due to the age of the hardware, mainly the LCD screens offered poor contrast.

Instead the game now runs on a 5x3m 3D Rear projection wall in the Vicon suite, and makes use of paralax motion tracking (Inspired from:

). It makes use of 3D ontop of the paralax to give an incredible effect of the world ajoining through the screen.

Video showing the paralax motion in action, notice how the effect is lost when tracking is lost in the 5th seccond. Although this is recoreded in 2D, the mouse seems to float far infront of the world purely by the paralax illusion. In 3D this effect is hightened, and the gun appears to float far infront of the screen as if the user is holding it.

[youtube=http://youtu.be/HEabUd_E-UM]','Motion Capture Parallax FPS

 

 A consumer con? 

 

UMPTOOL 4.02 (Not sure if backwards compatable with 2091)

You can also check out the flashboot.ru directory for a flasher if you have another other brand of USB:

In this post I aim to explain how to get Red alert 2 and Yuri's revenge working on Windows 7

Contents:

1. Running on win 7

2. Lan Play

3. Lan Patch issues

4. Copyprotection

5. Maps

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If when starting RA2:YR on Windows vista or Windows 7 you are greeted with:

***FATAL*** String Manager Failed to Initialize Properly

In vista the simple trick was to right click and run the game as an administrator. This allowed the game to access the stringmanager dlls.

For me only disabling User account control (UAC) worked. This is because uac is a lot more forceful in windows 7 and won't allow RA2.exe to access the string manager .dll's in the windows directory.

1) Open control panel

2) Click users

3) Click Modify User access control settings.

4) Set the status to "Never notify"

5) Accept the series of warnings.

6) Reboot your machine.

You can now run RA2:YR once your computer reboots.

If this fails to work first time, It might be an idea to enable windows 2000 compatibility mode on every exe in the ra2 folder.

After playing Yuri its recommended you turn UAC back on, Repeat the steps above, setting it back to the default setting:

Lan Play

At the time of Vista, Microsoft had stopped supporting the IPX protocol, which is required by RA2 to perform network play. Luckily some bright sparks managed to hack the games code to make it run on the UDP protocol, which all machines support!

This is dubbed as the lan patch.

There are 2 ways to obtain the lan patch (depending on your boxed copy)

If you have "The first decade" version of Yuri, its easiest if you get the unofficial 1.03 patch. Google "TFD 1.03" or click below.

This allows you to play without the need of the TFD disk (unbelievably useful)!

More importantly, it contains the lan patch, and installs it all for you! It replaces the network dll (wsock.dll) to use UDP instead of IPX.

If you are lucky enough to have the orignal box set, you'll need the stand alone IPX->UDP patch.

Download below, unzip, and place the wsock.dll in the ".../westwood/ra2" folder overwriting the existing wsock.dll.

Download:

However, both methods share the same drawback:

2 modified wsock.dlls cannot talk to eachother in Internet play (lan play is fine however).

If you try, your game will disconnect as soon as you exit the game lobby with a black screen.

A simple fix however:

Rename wsock.dll in the ra2 folder to disable it (i.e wsock.dis)

Then name wsock.dis back (wsock.dll)

Units blow up at the start of the game?

If your units blow up every time you start the game, you have to reinstall.

This is due to the anti piracy switch in the game; If same 2 cd keys see each other (LAN or Internet), as they will trigger the switch causing your units to blow up at the start of every game. I'm not sure if there's a registry key to revert the change without having to reinstall.

But for me a quick reinstall works, or you could download a crack to remove the piracy switch altogether.

Maps

If you ever want to install additional maps, Simply place the map file (.mix) in the ra2 folder:

If you wish to make your own maps for Red Alert 2 Yuri's revenge, a official map editor exists:

Using the map editor, you can create levels for Yuris Revenge and Red alert 2 in both single player and multiplayer.