Promethe’s Blog Web, RIAs and chocolate spaghettis…

Quake 2′s 3D models in Flash 10

Loading and rendering Quake 2's maps is a challenge because Flash 10 doesn't handle complex 3D geometry very well. But what about a smaller count of polygons ? Say a 3D model for example... already done! What about an animated 3D model then?

Details, pictures and a demo application right after the jump...

MD2 file format

Quake 2 uses the MD2 file format  to store animated 3D models. It is a quite simple file format: each MD2 file stores a single mesh and its animations. Each animation is just copy of the original mesh with different positions for each vertex. The number of vertices and the indices are the same for each frame. Therefore, the MD2 file format is easy to adapt to the Flash Platform because no complicated shaders/bones are required to animate the model: you just have to display the right vertices!

But it is not THAT simple. Each animation is actually subdivided into frames (vertices really). Because storing a fluid animation would take a lot of frames (and a lot of memory), only a few keyframes are stored. When rendering, one must compute the interpolation coefficient between the current and the next keyframe and use it to get the interpolated vertices. The following code does it all:

var frame1	: Vector.<Number>	= _currentFrame.vertices;
var frame2	: Vector.<Number>	= _nextFrame.vertices;
var c2		: Number		= _frame - int(_frame);
var c1		: Number		= 1 - c2;
var length	: Number		= frame1.length;
 
for (var i : uint = 0; i < length; ++i)
	_vertices[i] = frame1[i] * c1 + frame2[i] * c2;

... and here is the demo application :

Flash 10 MD2 loader

What it does...

• load Quake 2's MD2 files
• basic z-sorting using faces barycenter
• add a "frame" property to the mesh to handle animations
• interpolate and update vertices only when necessary
• wireframe material (press "w")
• "free chase" camera (mouse click + drag'n'drop to turn around the model)

What it doesn't do...

• use BSP trees to handle z-sorting (1 BSP tree / frame takes a lot of time and memory...)
• loop through a specific animation
• read Quake 2's animation files

Known issue(s)

None. If you find one please let me know! Performance seems to be very good actually...