January 9, 2009 07:02pm pst

11.20.2008 at 06:02AM PST, ID: 23921466

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Diamond Square Algorithm Implementation Problem

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7.8

Zones:

OpenGL Graphics & Game Programming, 3D Game Programming, Microsoft Visual C++

Tags:

OpenGL/C

Im working on an implementation of the Diamon Square algortihm, and I can't quite seem to get it to look right.

I'm working off this tutorial http://www.lighthouse3d.com/opengl/terrain/index.php?mpd2 which might help explain some of my code.

The function that I know I need to change somehow is below.

It simply takes the min and max X/Z coordinates for the current square being subdivided (which index into an array of Y-Values where these min's and max's already have a Y value computed) and a displacement.

I'm pretty sure the step where I calculate a new midpoint is correct (setting E) but the part that I know is wrong is where I set the midpoint of each side (F G H I)

The forumla seems like it should work, but on high levels of recursion I see almost veritcal drops instead of a smoother transition:

http://img185.imageshack.us/img185/1323/failyh0.png

An alternate approach I tried that -almost- worked was just doing:

yMap[xMin][zMidpnt] = (A + C ) / 2; // F
yMap[xMidpnt][zMin] = (A + B) / 2 ; // G
yMap[xMax][zMidpnt] = (B + D)/ 2; // H
yMap[xMidpnt][zMax] = (C + D) / 2 ; // I

Which produces a more better landscape but isn't really performing the square step of the algorithm correctly (I think) because it does not add any random displacement to these midpoints.

Any help on how to fix this would be appreciated.

         
           
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             void genLandscapeRec(int xMin, int xMax, int zMin, int zMax, float disp) {
 
   float nDisp =  (float)(disp * (float)pow(2, -(double)roughnes)); // New displacement
 
   int xMidpnt = (xMin+xMax) / 2;
   int zMidpnt = (zMin+zMax) / 2;
 
   GLfloat A = yMap[xMin][zMin];
   GLfloat B = yMap[xMax][zMin];
   GLfloat C = yMap[xMin][zMax];
   GLfloat D = yMap[xMax][zMax];
 
   GLfloat E = (A + B + C + D) / 4 + randDisp(disp); // Midpoint height
 
   yMap[xMidpnt][zMidpnt] = E; // Set E
 
   yMap[xMin][zMidpnt] = (A + C + E) / 3 + randDisp(disp);  // F
   yMap[xMidpnt][zMin] = (A + B + E) / 3 + randDisp(disp);  // G
   yMap[xMax][zMidpnt] = (B + D + E) / 3 + randDisp(disp);  // H
   yMap[xMidpnt][zMax] = (C + D + E) / 3 + randDisp(disp);  // I
 
   if ((xMidpnt - xMin) > 1) { // Subdivide if new midpoint length will be > 1
 
      genLandscapeRec(xMin, xMidpnt, zMin, zMidpnt, nDisp);
      genLandscapeRec(xMidpnt, xMax, zMin, zMidpnt, nDisp);
      genLandscapeRec(xMin, xMidpnt, zMidpnt, zMax, nDisp);
      genLandscapeRec(xMidpnt, xMax, zMidpnt, zMax, nDisp);
   }
}
 
float randDisp(float disp) {
 
    return (((float)rand()) / ((float)RAND_MAX)) * (disp + (disp/3)) - disp/3;
}

           
         

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