dpsv

01-15-2002, 05:16 AM

Hi ,

Following is the source code which I use to split a polygon by a plane. Sometimes the polygons that are split are not correct and I can't seem to understand why. The source code is a pascal code found on Delphi3d.net web site which I changed to suit my needs. Please help me in fixing this.

If I traverse the polygon list to find the best node (that leads to less splits of polygon) rather than using the first polygon/plane of my list as the split plane, then my BSP works good, but it takes enormous time to calculate.

Recpolygon has following fields

vec4dbl = array[1..4] of double;

Shaderpolyarr = Array[1..MaxPoints] of point;

RecPolygon = RECORD

npnts : Integer;

plane : vec4dbl;

Clr : Integer;

transp : Single;

poly : Shaderpolyarr;

END;

procedure SplitPoly(tri: RecPolygon; plane: vec4dbl; var inpnts, outpnts: RecPolygon);

const

eps = 0.0001;

var

ptA, ptB, v: point;

sideA, sideB, factor: double;

i: Integer;

begin

{ Slice a polygon in half using the supplied partitioning plane. The procedure

creates front and back, two arrays of triangles. }

inpnts := tri;

inpnts.npnts := 0;

outpnts := tri;

outpnts.npnts := 0;

// Acquire the normal/color/transparency properties for the new polygons

ptA := tri.poly[tri.npnts];

sideA := DistToPlane(plane, ptA);

for i := 1 to tri.npnts do

begin

ptB := tri.poly[i];

sideB := DistToPlane(plane, ptB);

if sideB > EPS then

begin

if sideA < -EPS then

begin

v := subpnt(ptB, ptA);

factor := -DistToPlane(plane, ptA) / cgDotProduct(Plane2Pnt(plane), v);

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := AddPnt(ptA, mulpnt(v, factor));

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := outpnts.poly[outpnts.npnts];

end;

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := ptB;

end

else if sideB < -EPS then

begin

if sideA > EPS then

begin

v := subpnt(ptB, ptA);

factor := -DistToPlane(plane, ptA) / cgDotProduct(Plane2Pnt(plane), v);

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := AddPnt(ptA, mulpnt(v, factor));

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := outpnts.poly[outpnts.npnts];

end;

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := ptB;

end

else begin

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := ptB;

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := ptB;

end;

ptA := ptB;

sideA := sideB;

end;end;

Thanks

DP

Following is the source code which I use to split a polygon by a plane. Sometimes the polygons that are split are not correct and I can't seem to understand why. The source code is a pascal code found on Delphi3d.net web site which I changed to suit my needs. Please help me in fixing this.

If I traverse the polygon list to find the best node (that leads to less splits of polygon) rather than using the first polygon/plane of my list as the split plane, then my BSP works good, but it takes enormous time to calculate.

Recpolygon has following fields

vec4dbl = array[1..4] of double;

Shaderpolyarr = Array[1..MaxPoints] of point;

RecPolygon = RECORD

npnts : Integer;

plane : vec4dbl;

Clr : Integer;

transp : Single;

poly : Shaderpolyarr;

END;

procedure SplitPoly(tri: RecPolygon; plane: vec4dbl; var inpnts, outpnts: RecPolygon);

const

eps = 0.0001;

var

ptA, ptB, v: point;

sideA, sideB, factor: double;

i: Integer;

begin

{ Slice a polygon in half using the supplied partitioning plane. The procedure

creates front and back, two arrays of triangles. }

inpnts := tri;

inpnts.npnts := 0;

outpnts := tri;

outpnts.npnts := 0;

// Acquire the normal/color/transparency properties for the new polygons

ptA := tri.poly[tri.npnts];

sideA := DistToPlane(plane, ptA);

for i := 1 to tri.npnts do

begin

ptB := tri.poly[i];

sideB := DistToPlane(plane, ptB);

if sideB > EPS then

begin

if sideA < -EPS then

begin

v := subpnt(ptB, ptA);

factor := -DistToPlane(plane, ptA) / cgDotProduct(Plane2Pnt(plane), v);

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := AddPnt(ptA, mulpnt(v, factor));

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := outpnts.poly[outpnts.npnts];

end;

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := ptB;

end

else if sideB < -EPS then

begin

if sideA > EPS then

begin

v := subpnt(ptB, ptA);

factor := -DistToPlane(plane, ptA) / cgDotProduct(Plane2Pnt(plane), v);

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := AddPnt(ptA, mulpnt(v, factor));

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := outpnts.poly[outpnts.npnts];

end;

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := ptB;

end

else begin

outpnts.npnts := outpnts.npnts + 1;

outpnts.poly[outpnts.npnts] := ptB;

inpnts.npnts := inpnts.npnts + 1;

inpnts.poly[inpnts.npnts] := ptB;

end;

ptA := ptB;

sideA := sideB;

end;end;

Thanks

DP