Kugel

Variante 1

Der nachfolgende Code ist ein Port von http://astronomy.swin.edu.au/~pbourke/opengl/sphere/.

Neben den Vertexpositionen werden die Normalen und Texturkoordinaten berechnet.

TVector3f ist ein einfaches Feld mit 3 Floats. (array[0..2] of float)

procedure CreateSphere(c: TVector3f; r: Single; n: Integer);
const
  TWOPI = PI*2;
  PID2 = PI/2;
var
  i,j: Integer;
  theta1,theta2,theta3: Single;
  e,p:TVector3f;
begin
  if (r < 0) then r := -r;
  if (n < 0) then n := -n;
  if (n < 4) or (r <= 0) then
  begin
    glBegin(GL_POINTS);
      glVertex3f(c[0],c[1],c[2]);
    glEnd;
    exit;
  end;

  for j:=0 to n div 2 do
  begin
    theta1 := j * TWOPI / n - PID2;
    theta2 := (j + 1) * TWOPI / n - PID2;

    glBegin(GL_QUAD_STRIP);
    for i:=0 to n do
    begin
      theta3 := i * TWOPI / n;

      e[0] := cos(theta2) * cos(theta3);
      e[1] := sin(theta2);
      e[2] := cos(theta2) * sin(theta3);
      p[0] := c[0] + r * e[0];
      p[1] := c[1] + r * e[1];
      p[2] := c[2] + r * e[2];

      glNormal3f(e[0],e[1],e[2]);
      glTexCoord2f(i/n,2*(j+1)/n);
      glVertex3f(p[0],p[1],p[2]);

      e[0] := cos(theta1) * cos(theta3);
      e[1] := sin(theta1);
      e[2] := cos(theta1) * sin(theta3);
      p[0] := c[0] + r * e[0];
      p[1] := c[1] + r * e[1];
      p[2] := c[2] + r * e[2];

      glNormal3f(e[0],e[1],e[2]);
      glTexCoord2f(i/n,2*j/n);
      glVertex3f(p[0],p[1],p[2]);
    end;
   glEnd;
  end;
end;

Variante 2

Der nachfolgende Code ist selbst geschrieben (MatReno)

TVector2f : Array [0..1] of Single;

TVector3f : Array [0..2] of Single;

Procedure DrawSphereObject(radius: Single; n: word; 
                           typ: byte; inverted: boolean; 
                           voffset: TVector3f; toffset, tscale: TVector2f);
Var alpha   : TVector2f;  // i*beta around x axis
    SinAlpha: TVector2f;  // sin(alpha)
    CosAlpha: TVector2f;  // cos(alpha)
    beta    : Single;     // DegToRad(360° / n)
    delta   : Single;     // j*beta around z axis
    SinDelta: Single;     // sin(delta)
    CosDelta: Single;     // cos(delta)
    h, q    : word;       // half, quarter
    v       : TVector3f;  // vector for normal and vertex
    border  : TVector4i;  // for-loop borders
    i, j    : Integer;
    k       : Byte;
Begin
  radius := abs(radius);

  If (n < 4) Or (Odd(n)) Or (radius = 0) Then Exit;

  h := n div 2;
  q := n div 4;
  If (Odd(h)) Then inc(q);

  Case typ of
    0: border := ToVector4i(  -h,    h-1, -q, q);  // sphere
    1: border := ToVector4i(  -h,    h-1, -q, 0);  // hemisphere x-
    2: border := ToVector4i(  -h,    h-1,  0, q);  // hemisphere x+
    3: border := ToVector4i(-h-q, -h+q-1, -q, q);  // hemisphere y-
    4: border := ToVector4i(  -q,    q-1, -q, q);  // hemisphere y+
    5: border := ToVector4i(  -h,     -1, -q, q);  // hemisphere z-
    6: border := ToVector4i(   0,    h-1, -q, q);  // hemisphere z+
    else Exit;
  End;

  beta := 2*PI / n;

    For i:=border[0] to border[1] do Begin
      alpha := ToVector2f(i*beta, (i+1)*beta);

      SinAlpha := ToVector2f(sin(alpha[0]), sin(alpha[1]));
      CosAlpha := ToVector2f(cos(alpha[0]), cos(alpha[1]));

      glBegin(GL_TRIANGLE_STRIP);
      For j:=border[2] to border[3] do Begin
        delta := j*beta;

        SinDelta := sin(delta);
        CosDelta := cos(delta);

        If (inverted) Then
          For k:=1 downto 0 do Begin
            v := ToVector3f(-SinDelta, -CosAlpha[k]*CosDelta, -SinAlpha[k]*CosDelta);
            glNormal3fv(@v);
            v := VectorAdd(VectorMult(v, -radius), voffset);
            glTexCoord2f((j/n + 0.25)*tscale[0] + toffset[0], ((i+k)/n)*tscale[1] + toffset[1]);
            glvertex3fv(@v);
          End;

        If (not inverted) Then
          For k:=0 to 1 do Begin
            v := ToVector3f(SinDelta, CosAlpha[k]*CosDelta, SinAlpha[k]*CosDelta);
            glNormal3fv(@v);
            v := VectorAdd(VectorMult(v,  radius), voffset);
            glTexCoord2f((j/n + 0.25)*tscale[0] + toffset[0], ((i+k)/n)*tscale[1] + toffset[1]);
            glvertex3fv(@v);
          End
      End;
      glEnd;
   End;
End;

Um eine Kugel zu rendern muss man folgendes aufrufen:

    DrawSphereObject(radius, n, 0, false, NULL_VECTOR_3f, NULL_VECTOR_2f, ToVector2f(2*tscale[0], tscale[1]));