LZScene

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//
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// This unit is part of the GLScene Engine https://github.com/glscene
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//
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{
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    Code to generate triangle strips and fans for polygons.
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  History :  
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       23/08/10 - Yar - Added OpenGLTokens to uses, replaced OpenGL1x functions to OpenGLAdapter
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       06/06/10 - Yar - Fixed warnings
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       26/11/09 - DaStr - Improved Lazarus compatibility (BugtrackerID = 2893580)
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       10/03/09 - DanB - DoTesselate now accepts TGLBaseMesh instead of
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                            TGLFreeform, so can now use TGLActor with it too
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       29/05/08 - DaStr - Added $I GLScene.inc
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       08/09/03 - Jaj - Added single outline polygon support
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  License: 
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    Contributed to GLScene.
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}
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unit GLGLUTesselation;
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interface
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{$I GLScene.inc}
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uses
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  GLVectorFileObjects,
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  GLVectorLists,
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  GLVectorGeometry;
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{ Tesselates the polygon outlined by the Vertexes. And addeds them to the first facegroup of the Mesh. }
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procedure DoTesselate(Vertexes: TAffineVectorList; Mesh: TGLBaseMesh; normal: PAffineVector = nil; invertNormals: Boolean = False);
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implementation
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uses
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  SysUtils,
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  OpenGLAdapter,
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  OpenGLTokens,
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  GLVectorTypes;
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var
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  TessMesh: TGLMeshObject;
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  TessFace: TFGIndexTexCoordList;
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  TessExtraVertices: Integer;
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  TessVertices: PAffineVectorArray;
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procedure DoTessBegin(mode: TGLEnum);
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{$IFDEF Win32} stdcall;
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{$ENDIF}{$IFDEF UNIX} cdecl;
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{$ENDIF}
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begin
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  TessFace := TFGIndexTexCoordList.CreateOwned(TessMesh.FaceGroups);
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  case mode of
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    GL_TRIANGLES: TessFace.Mode := fgmmTriangles;
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    GL_TRIANGLE_STRIP: TessFace.Mode := fgmmTriangleStrip;
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    GL_TRIANGLE_FAN: TessFace.Mode := fgmmTriangleFan;
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  end;
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end;
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procedure DoTessVertex3fv(v: PAffineVector);
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{$IFDEF Win32} stdcall;
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{$ENDIF}{$IFDEF UNIX} cdecl;
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{$ENDIF}
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begin
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  TessFace.Add(TessMesh.Vertices.Add(v^), 0, 0);
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end;
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procedure DoTessEnd;
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{$IFDEF Win32} stdcall;
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{$ENDIF}{$IFDEF UNIX} cdecl;
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{$ENDIF}
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begin
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end;
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procedure DoTessError(errno: TGLEnum);
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{$IFDEF Win32} stdcall;
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{$ENDIF}{$IFDEF UNIX} cdecl;
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{$ENDIF}
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begin
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  Assert(False, IntToStr(errno) + ': ' + string(gluErrorString(errno)));
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end;
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function AllocNewVertex: PAffineVector;
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begin
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  Inc(TessExtraVertices);
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  Result := @TessVertices[TessExtraVertices - 1];
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end;
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procedure DoTessCombine(coords: PDoubleVector; vertex_data: Pointer; weight: PGLFloat; var outData: Pointer);
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{$IFDEF Win32} stdcall;
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{$ENDIF}{$IFDEF UNIX} cdecl;
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{$ENDIF}
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begin
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  outData := AllocNewVertex;
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  SetVector(PAffineVector(outData)^, coords[0], coords[1], coords[2]);
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end;
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procedure DoTesselate(Vertexes: TAffineVectorList; Mesh: TGLBaseMesh; normal: PAffineVector = nil; invertNormals: Boolean = False);
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var
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  Tess: PGLUTesselator;
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  i: Integer;
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  dblVector: TAffineDblVector;
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begin
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  // Select or Create FaceGroup
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  if Mesh.MeshObjects.Count = 0 then
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  begin
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    TessMesh := TGLMeshObject.CreateOwned(Mesh.MeshObjects);
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    Mesh.MeshObjects[0].Mode := momFaceGroups;
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  end
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  else
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    TessMesh := Mesh.MeshObjects[0];
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  // allocate extra buffer used by GLU in complex polygons.
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  GetMem(TessVertices, Vertexes.Count * SizeOf(TAffineVector));
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  // make a Tessellation GLU object.
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  Tess := gluNewTess;
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  // set up callback events
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  gluTessCallback(Tess, GLU_TESS_BEGIN, @DoTessBegin);
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  gluTessCallback(tess, GLU_TESS_VERTEX, @DoTessVertex3fv);
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  gluTessCallback(tess, GLU_TESS_END, @DoTessEnd);
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  gluTessCallback(tess, GLU_TESS_ERROR, @DoTessError);
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  gluTessCallback(tess, GLU_TESS_COMBINE, @DoTessCombine);
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  if Assigned(normal) then
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    gluTessNormal(tess, normal^.V[0], normal^.V[1], normal^.V[2])
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  else
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    gluTessNormal(tess, 0, 1, 0);
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  // start tesselation of polygon
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  gluTessBeginPolygon(tess, nil);
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  // build outline, a polygon can have multiple outlines.
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  gluTessBeginContour(tess);
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  TessExtraVertices := 0;
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  if invertNormals then
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  begin
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    for i := Vertexes.Count - 1 downto 0 do
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    begin
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      SetVector(dblVector, Vertexes.Items[i]);
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      gluTessVertex(tess, dblVector, Vertexes.ItemAddress[i]);
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    end;
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  end
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  else
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  begin
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    for i := 0 to Vertexes.Count - 1 do
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    begin
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      SetVector(dblVector, Vertexes.Items[i]);
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      gluTessVertex(tess, dblVector, Vertexes.ItemAddress[i]);
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    end;
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  end;
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  gluTessEndContour(tess);
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  // End Tesselation of polygon, THIS is where the data is processed! (And all the events triggered!)
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  gluTessEndPolygon(tess);
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  // Destroy the Tessellation GLU object.
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  gluDeleteTess(tess);
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  // deallocate extra buffer used by GLU in complex polygons.
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  FreeMem(TessVertices, Vertexes.Count * SizeOf(TAffineVector));
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end;
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end.
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