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voxlap5 parallel projection

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• intripoon at 2007-08-22 06:55
  Hi !
  
  How would I go to add parallel projection to voxlap?
  
  In opticast, there seems to be this part
  
  

  
  	gstartv = (char *)*(long *)gpixy;
  	if (glipos.z >= gstartv[1])
  	{
  		do
  		{
  			if (!gstartv[0]) return;
  			gstartv += gstartv[0]*4;
  		} while (glipos.z >= gstartv[1]);
  		if (glipos.z < gstartv[3]) return;
  		gstartz0 = gstartv[3];
  	} else gstartz0 = 0;
  	gstartz1 = gstartv[1];
  

  
  that searches for the right interval in the rle height colums for the position of the camera. I think I have to do this multiple times for parallel projection. But the following lines are hard to decipher. There seem to be 4 cases that are ahndled seperatly. I'ld expect some loop that crawls through the screen columns and calculate a new direction vector each time. Do you know the meaning of the various variables used in opticast? Also the format of the rle colums would be interesting.
  
  I'ld like to try implementing a 3D Modelling tool prototype to see if it could be of any use. I imagine something like Gimp but 3D or ZBrush, but without ZBrush's limitations (like not being able to cut holes in your object). Afterwards one could calculate a polygon model from the voxel modell.
  
  Here is the prototype so far: http://www.marc.transmogrifier.de/projects/voxeleditor/. I think it defenately lacks parallel projection for modelling.
  
  Greetings
      Marc
  
• Awesoken at 2007-08-22 14:14

  Re: voxlap5 parallel projection

  How would I go to add parallel projection to voxlap?

  Oh my. You are taking an engine that wasn't designed for modelling, and now you are asking to remove one of its best features. I respect all the work you did by integrating Voxlap into your modelling program, but I'm afraid you started with the wrong engine. Modifying Voxlap to support parallel projection would be very difficult.

  I think I have to do this multiple times for parallel projection.

  You would have to do a lot more than that. Perspective is burned into my raycasting core, and that's written in assembler code. Good luck with that.
  You would be much better off with a splat-based renderer for your modeller. Have you tried SLAB6? It's my own voxel modelling program. It might not have the interface that you desire, but it would be a much more sensible base of code to start with. SLAB6 supports orthographic perspective.

  There seem to be 4 cases that are ahndled seperatly.

  The 4 blocks of code at the end of opticast() handle raycasting in the 4 directions along the screen. I divide these quadrants in a way that maximizes detail per rendering cost.

  Do you know the meaning of the various variables used in opticast?

  Sure, I wrote it.

  Also the format of the rle colums would be interesting.

  I provide a description inside a comment at the top of VOXLAP5.C. Search for "vbuf format". You will also need "sptr", which tells you where column (x,y) is located in memory.
  
  For orthographic projection, there exists an exotic rendering technique called fourier volume rendering. It probably won't be useful to your project, but I thought I'd mention it just for fun: http://www.eecg.toronto.edu/~fender/fvr/index.html