Problems with gluTessProperty in GLScene and GLU_TESS_WINDING_POSITIVE
rule.
lazarus / 70-OpenGL

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Wodzu · 2010-02-20 15:37

Hi guys.

I am starting to learn OpenGL. I've tried to tesselate a 5-point star
polygon. The problem is that when I want to use winding rule
GLU_TESS_WINDING_POSITIVE I am getting a SIGSEGV error. 

Also when I want to use more then one contour the same error occurs.

Here is the code:

Code: [Select]program TessError;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Classes
  { you can add units after this },
  SysUtils, gl, glu, glut;

{$R TessError.res}

type
  TCoords = array[0..2] of GLdouble;
  PCoords = ^TCoords;
  TVertexData = array[0..3] of GLdouble;
  PVertexData = ^TVertexData;
  TWeight = array[0..3] of GLfloat;

const
  AppWidth = 640;
  AppHeight = 480;

var
  ScreenWidth, ScreenHeight, StarSize: Integer;
  StarCoords: array[0..4] of T3DArray = ((0.0, 2.0, 0), (-1.0, -1.6,
0),
                                        (1.8, 0.6, 0), (-1.8, 0.6, 0),
                                        (1.0, -1.6, 0));
  BoxCoords: array[0..3] of T3dArray = ((0.5, 0.5, 0), (-0.5, 0.5, 0),
(-0.5, -0.5, 0),
                                        (0.5, -0.5, 0));
  ListID: Integer;

procedure GLDrawScene; cdecl;
var
  i: Integer;
begin
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity;
  glOrtho(-10.0, 10.0, -10.0, 10.0, -1.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
  glColor3f(1.0, 1.0, 1.0);
  glCallList(ListID);
  glColor3f(1.0, 0.0, 1.0);
  glBegin(GL_LINES);
    glVertex3f(0.0, 10.0, 0);
    glVertex3f(0.0, -10, 0);
  glEnd();
  glBegin(GL_LINES);
    glVertex3f(-10.0, 0.0, 0);
    glVertex3f(10.0, 0, 0);
  glEnd();
  glFlush();
  glutSwapBuffers;
end;

procedure InitializeGL;
begin
  glClearColor(0.0, 0.0, 0.0, 0);
end;

procedure GLResize(Width, Height: Integer); cdecl;
begin
  if Height = 0 then
    Height := 1;

  glViewport(0, 0, Width, Height);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity;
  glOrtho(-10.0, 10.0, -10.0, 10.0, -1.0, 1.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity;
end;

procedure GLKeyboard(Key: Byte; X, Y: Longint); cdecl;
begin
  if Key = 27 then
    Halt(0);
end;

procedure glutInitPascal(ParseCmdLine: Boolean);
var
  Cmd: array of PChar;
  CmdCount, I: Integer;
begin
  if ParseCmdLine then
    CmdCount := ParamCount + 1
  else
    CmdCount := 1;
  SetLength(Cmd, CmdCount);
  for I := 0 to CmdCount - 1 do
    Cmd[I] := PChar(ParamStr(I));
  glutInit(@CmdCount, @Cmd);
end;

procedure TessBegin(which: GLEnum); cdecl;
begin
  glBegin(which);
end;

procedure TessEnd; cdecl;
begin
  glEnd();
end;

procedure TessVertex(data: Pointer); cdecl;
begin
  glVertex3dv(PGLDouble(data));
end;

procedure TessCombine(Coords: PCoords; VData: Pointer; Weight:
PglFloat; out DataOut: Pointer); cdecl;
begin
  DataOut := GetMem(3 * SizeOf(GLdouble));
  PCoords(DataOut)^[0] := Coords^[0];
  PCoords(DataOut)^[1] := Coords^[1];
  PCoords(DataOut)^[2] := Coords^[2];
end;

procedure TessError(errno : TGLEnum); cdecl;
begin
   Assert(False, IntToStr(errno)+': '+gluErrorString(errno));
end;


procedure Tesselation;
var
  Tesselator: PGLUtesselator;
begin
  ListID := glGenLists(1);
  Tesselator := gluNewTess();
  gluTessCallback(Tesselator, GLU_TESS_BEGIN, TCallBack(@TessBegin));
  gluTessCallback(Tesselator, GLU_TESS_END, TCallBack(@TessEnd));
  gluTessCallback(Tesselator, GLU_TESS_VERTEX,
TCallBack(@TessVertex));
  gluTessCallback(Tesselator, GLU_TESS_COMBINE,
TCallBack(@TessCombine));
  gluTessCallback(Tesselator, GLU_TESS_ERROR, TCallBack(@TessError));
  glNewList(ListID, GL_COMPILE);
//    gluTessProperty(Tesselator, GLU_TESS_WINDING_RULE,
GLU_TESS_WINDING_POSITIVE);  //uncomment this and you will get error
    gluTessBeginPolygon(Tesselator, nil);
      gluTessBeginContour(Tesselator);
        gluTessVertex(Tesselator, StarCoords[0], @StarCoords[0]);
        gluTessVertex(Tesselator, StarCoords[1], @StarCoords[1]);
        gluTessVertex(Tesselator, StarCoords[2], @StarCoords[2]);
        gluTessVertex(Tesselator, StarCoords[3], @StarCoords[3]);
        gluTessVertex(Tesselator, StarCoords[4], @StarCoords[4]);
      gluTessEndContour(Tesselator);
      {gluTessBeginContour(Tesselator);  //uncomment this and you will
get error
        gluTessVertex(Tesselator, BoxCoords[0], @BoxCoords[0]);
        gluTessVertex(Tesselator, BoxCoords[1], @BoxCoords[1]);
        gluTessVertex(Tesselator, BoxCoords[2], @BoxCoords[2]);
        gluTessVertex(Tesselator, BoxCoords[3], @BoxCoords[3]);
      gluTessEndContour(Tesselator); }
    gluTessEndPolygon(Tesselator);
  glEndList;
  gluDeleteTess(Tesselator);
end;

begin
  glutInitPascal(False);
  glutInitDisplayMode(GLUT_DOUBLE or GLUT_RGB or GLUT_DEPTH);
  glutInitWindowSize(AppWidth, AppHeight);
  ScreenWidth := glutGet(GLUT_SCREEN_WIDTH);
  ScreenHeight := glutGet(GLUT_SCREEN_HEIGHT);
  glutInitWindowPosition((ScreenWidth - AppWidth) div 2, (ScreenHeight
- AppHeight) div 2);
  glutCreateWindow('TessError');
  InitializeGL;
  Tesselation;
  glutDisplayFunc(@GLDrawScene);
  glutReshapeFunc(@GLResize);
  glutKeyboardFunc(@GLKeyboard);

  glutMainLoop;
end.
What am I doing wrong?

Also, could you recommend me some Pascal-based OpenGL newsgroups?
Only newsgroup which I've found is here:
news://forums.talkto.net/glscene.general but it doesn't seem to
work...:|

Thanks for your time.

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Rustam Asmandiarov · 2010-03-03 17:52

Hi! If you in Windows try it
{$IFDEF Win32} stdcall; {$ENDIF} {$IFDEF UNIX} cdecl; {$ENDIF}
In last version GLScene Pipe normally works.

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Wodzu · 2010-03-08 13:04

Hi Rustam.

Yes that was the problem, unfortunately wiki tutorial about FPC and
OpenGL doesn't say about different calling convetions under different
OS.

Thanks for the answer tough.