HollowCylinder.java :  » Graphics-3D-2D-OpenGL » min3d » min3d » objectPrimitives » Android Open Source

package min3d.objectPrimitives;

import min3d.core.Object3dContainer;
import min3d.vos.Color4;
import min3d.vos.Face;
import min3d.vos.Number3d;
import min3d.vos.Uv;

/**
 * Example of a more complex programmatically-drawn object.
 * 
 * Unfortunately, because the object's faces share as many vertices as possible,
 * shading is incorrect on the cylinder surfaces.
 *  
 * To fix would require duplicating vertices, adding new normals, 
 * and generally reworking algorithm. Yek.
 */
public class HollowCylinder extends Object3dContainer 
{
  private double DEG = Math.PI / 180;
  
  private int _segs;
  private float _radiusOuter;
  private float _radiusInner;
  private float _height;
  

  public HollowCylinder(float $radiusOuter, float $radiusInner, float $height, int $segs)
  {
    super($segs * 4, $segs * 8);
    
    _segs = $segs;
    _height = $height;
    _radiusOuter = $radiusOuter;
    _radiusInner = $radiusInner;
    
    addHorizontalSurface(false, _height / +2);
    addHorizontalSurface(true, _height / -2);
    addVerticalSurface(true);
    addVerticalSurface(false);
  }
  
  private void addHorizontalSurface(boolean $isTopSide, float $zOffset)
  {
    int indexOffset = _vertices.size();
    float step = (float)((360.0 / _segs) * DEG);

    // verts
    
    Color4 col = $isTopSide ? new Color4(255,0,0,255) : new Color4(0,255,0,255);
    
    for (int i = 0; i < _segs; i++)
    {
      float angle = (float)i * step;

      // outer 
      float x1     = (float) Math.sin(angle) * _radiusOuter;
      float y1     = (float) Math.cos(angle) * _radiusOuter;
      float z1     = $zOffset; 
      Uv uv1       = new Uv(x1,y1);
      Number3d n1   = new Number3d(0,0, $isTopSide ? -1 : +1);
      this.vertices().addVertex(new Number3d(x1,y1,z1), uv1, n1, col);

      // inner 
      float x2     = (float) Math.sin(angle) * _radiusInner;
      float y2     = (float) Math.cos(angle) * _radiusInner;
      float z2     = $zOffset; 
      Uv uv2      = new Uv(x2,y2);
      Number3d n2  = new Number3d(0,0, $isTopSide ? -1 : +1);
      this.vertices().addVertex(new Number3d(x2,y2,z2), uv2, n2, col);
    }
    
    // indicies
    
    for (int i = 2; i <= _segs; i++)
    {
      int a = indexOffset  +  i*2 - 3 - 1;
      int b = indexOffset  +  i*2 - 2 - 1;
      int c = indexOffset  +  i*2 - 1 - 1;
      int d = indexOffset  +  i*2 - 0 - 1;
      addQuad(a,b,c,d, $isTopSide);
    }    
  
    int a = indexOffset  +  _segs*2 - 1 - 1; // ... connect last segment
    int b = indexOffset  +  _segs*2 - 0 - 1;
    int c = indexOffset  +  0;
    int d = indexOffset  +  1;
    addQuad(a,b,c,d, $isTopSide);
  }
  
  // 
  private void addVerticalSurface(boolean $isOuter)
  {
    int off = (int)(_vertices.size() / 2); 
    
    for (int i = 0; i < _segs - 1; i++)
    {
      int ul = i*2;
      int bl = ul + off;
      int ur = i*2 + 2;
      int br = ur + off;
      
      if (!$isOuter) {
        ul++;
        bl++;
        ur++;
        br++;
      }
      addQuad(ul,bl,ur,br, $isOuter);
    }
    
    int ul = (_segs-1)*2;
    int bl = ul + off;
    int ur = 0*2;
    int br = ur + off;

    if (!$isOuter) {
      ul++;
      bl++;
      ur++;
      br++;
    }

    addQuad(ul,bl,ur,br, $isOuter);
  }
  
  private void addQuad(int ul, int bl, int ur, int br, boolean $flipped)
  {
    Face t;
    
    if (! $flipped)
    {
      _faces.add((short)ul,(short)bl,(short)ur);
      _faces.add((short)bl,(short)br,(short)ur);
    }
    else
    {
      _faces.add((short)ur,(short)br,(short)ul);
      _faces.add((short)br,(short)bl,(short)ul);
    }
  }
}