Draw a polygon with Gouraud shading
01.01.2007
uses
Graphics, Dialogs;
TRGBFloat = record
R : single;
G : single;
B : single;
end;
TPointColor = record
X : integer;
Y : integer;
RGB : TRGBFloat;
end;
TPointColorTriangle = array[0..2] of TPointColor;
{This procedure draws a triangular polygon using Gouraud shading.
You specify the position and colour of the 3 corners and it will
draw a filled triangle with the colours smoothed out over the
surface of the polygon. This is used a lot in 3D graphics for
improved rendering of curved surfaces. The procedure is very fast
and can be used for realtime 3D animation.}
// fill a traingular polygon using Gouraud shading
procedure T3DModel.GouraudPoly(var ABitmap : TBitmap ; V : TPointColorTriangle);
Var
LX, RX, Ldx, Rdx : Single;
Dif1, Dif2 : Single;
LRGB, RRGB, RGB, RGBdx, LRGBdy, RRGBdy : TRGBFloat;
RGBT : RGBTriple;
Scan : PRGBTripleArray;
y, x, ScanStart, ScanEnd : integer;
Vmax : byte;
Right : boolean;
Temp : TPointColor;
begin
try
// sort vertices by Y
Vmax := 0;
if V[1].Y > V[0].Y then Vmax := 1;
if V[2].Y > V[Vmax].Y then Vmax := 2;
if Vmax <> 2 then begin
Temp := V[2];
V[2] := V[Vmax];
V[Vmax] := Temp;
end;
if V[1].Y > V[0].Y then Vmax := 1
else Vmax := 0;
if Vmax = 0 then begin
Temp := V[1];
V[1] := V[0];
V[0] := Temp;
end;
Dif1 := V[2].Y - V[0].Y;
if Dif1 = 0 then Dif1 := 0.001; // prevent EZeroDivide
Dif2 := V[1].Y - V[0].Y;
if Dif2 = 0 then Dif2 := 0.001;
{ work out if middle point is to the left or right of the line
connecting upper and lower points }
if V[1].X > (V[2].X - V[0].X) * Dif2 / Dif1 + V[0].X then Right := True
else Right := False;
// calculate increments in x and colour for stepping through the lines
if Right then begin
Ldx := (V[2].X - V[0].X) / Dif1;
Rdx := (V[1].X - V[0].X) / Dif2;
LRGBdy.B := (V[2].RGB.B - V[0].RGB.B) / Dif1;
LRGBdy.G := (V[2].RGB.G - V[0].RGB.G) / Dif1;
LRGBdy.R := (V[2].RGB.R - V[0].RGB.R) / Dif1;
RRGBdy.B := (V[1].RGB.B - V[0].RGB.B) / Dif2;
RRGBdy.G := (V[1].RGB.G - V[0].RGB.G) / Dif2;
RRGBdy.R := (V[1].RGB.R - V[0].RGB.R) / Dif2;
end else begin
Ldx := (V[1].X - V[0].X) / Dif2;
Rdx := (V[2].X - V[0].X) / Dif1;
RRGBdy.B := (V[2].RGB.B - V[0].RGB.B) / Dif1;
RRGBdy.G := (V[2].RGB.G - V[0].RGB.G) / Dif1;
RRGBdy.R := (V[2].RGB.R - V[0].RGB.R) / Dif1;
LRGBdy.B := (V[1].RGB.B - V[0].RGB.B) / Dif2;
LRGBdy.G := (V[1].RGB.G - V[0].RGB.G) / Dif2;
LRGBdy.R := (V[1].RGB.R - V[0].RGB.R) / Dif2;
end;
LRGB := V[0].RGB;
RRGB := LRGB;
LX := V[0].X;
RX := V[0].X;
// fill region 1
for y := V[0].Y to V[1].Y - 1 do begin
// y clipping
if y > ABitmap.Height - 1 then Break;
if y < 0 then begin
LX := LX + Ldx;
RX := RX + Rdx;
LRGB.B := LRGB.B + LRGBdy.B;
LRGB.G := LRGB.G + LRGBdy.G;
LRGB.R := LRGB.R + LRGBdy.R;
RRGB.B := RRGB.B + RRGBdy.B;
RRGB.G := RRGB.G + RRGBdy.G;
RRGB.R := RRGB.R + RRGBdy.R;
Continue;
end;
Scan := ABitmap.ScanLine[y];
// calculate increments in color for stepping through pixels
Dif1 := RX - LX + 1;
if Dif1 = 0 then Dif1 := 0.001;
RGBdx.B := (RRGB.B - LRGB.B) / Dif1;
RGBdx.G := (RRGB.G - LRGB.G) / Dif1;
RGBdx.R := (RRGB.R - LRGB.R) / Dif1;
// x clipping
if LX < 0 then begin
ScanStart := 0;
RGB.B := LRGB.B + (RGBdx.B * abs(LX));
RGB.G := LRGB.G + (RGBdx.G * abs(LX));
RGB.R := LRGB.R + (RGBdx.R * abs(LX));
end else begin
RGB := LRGB;
ScanStart := round(LX);
end;
if RX - 1 > ABitmap.Width - 1 then ScanEnd := ABitmap.Width - 1
else ScanEnd := round(RX) - 1;
// scan the line
for x := ScanStart to ScanEnd do begin
RGBT.rgbtBlue := trunc(RGB.B);
RGBT.rgbtGreen := trunc(RGB.G);
RGBT.rgbtRed := trunc(RGB.R);
Scan[x] := RGBT;
RGB.B := RGB.B + RGBdx.B;
RGB.G := RGB.G + RGBdx.G;
RGB.R := RGB.R + RGBdx.R;
end;
// increment edge x positions
LX := LX + Ldx;
RX := RX + Rdx;
// increment edge colours by the y colour increments
LRGB.B := LRGB.B + LRGBdy.B;
LRGB.G := LRGB.G + LRGBdy.G;
LRGB.R := LRGB.R + LRGBdy.R;
RRGB.B := RRGB.B + RRGBdy.B;
RRGB.G := RRGB.G + RRGBdy.G;
RRGB.R := RRGB.R + RRGBdy.R;
end;
Dif1 := V[2].Y - V[1].Y;
if Dif1 = 0 then Dif1 := 0.001;
// calculate new increments for region 2
if Right then begin
Rdx := (V[2].X - V[1].X) / Dif1;
RX := V[1].X;
RRGBdy.B := (V[2].RGB.B - V[1].RGB.B) / Dif1;
RRGBdy.G := (V[2].RGB.G - V[1].RGB.G) / Dif1;
RRGBdy.R := (V[2].RGB.R - V[1].RGB.R) / Dif1;
RRGB := V[1].RGB;
end else begin
Ldx := (V[2].X - V[1].X) / Dif1;
LX := V[1].X;
LRGBdy.B := (V[2].RGB.B - V[1].RGB.B) / Dif1;
LRGBdy.G := (V[2].RGB.G - V[1].RGB.G) / Dif1;
LRGBdy.R := (V[2].RGB.R - V[1].RGB.R) / Dif1;
LRGB := V[1].RGB;
end;
// fill region 2
for y := V[1].Y to V[2].Y - 1 do begin
// y clipping
if y > ABitmap.Height - 1 then Break;
if y < 0 then begin
LX := LX + Ldx;
RX := RX + Rdx;
LRGB.B := LRGB.B + LRGBdy.B;
LRGB.G := LRGB.G + LRGBdy.G;
LRGB.R := LRGB.R + LRGBdy.R;
RRGB.B := RRGB.B + RRGBdy.B;
RRGB.G := RRGB.G + RRGBdy.G;
RRGB.R := RRGB.R + RRGBdy.R;
Continue;
end;
Scan := ABitmap.ScanLine[y];
Dif1 := RX - LX + 1;
if Dif1 = 0 then Dif1 := 0.001;
RGBdx.B := (RRGB.B - LRGB.B) / Dif1;
RGBdx.G := (RRGB.G - LRGB.G) / Dif1;
RGBdx.R := (RRGB.R - LRGB.R) / Dif1;
// x clipping
if LX < 0 then begin
ScanStart := 0;
RGB.B := LRGB.B + (RGBdx.B * abs(LX));
RGB.G := LRGB.G + (RGBdx.G * abs(LX));
RGB.R := LRGB.R + (RGBdx.R * abs(LX));
end else begin
RGB := LRGB;
ScanStart := round(LX);
end;
if RX - 1 > ABitmap.Width - 1 then ScanEnd := ABitmap.Width - 1
else ScanEnd := round(RX) - 1;
// scan the line
for x := ScanStart to ScanEnd do begin
RGBT.rgbtBlue := trunc(RGB.B);
RGBT.rgbtGreen := trunc(RGB.G);
RGBT.rgbtRed := trunc(RGB.R);
Scan[x] := RGBT;
RGB.B := RGB.B + RGBdx.B;
RGB.G := RGB.G + RGBdx.G;
RGB.R := RGB.R + RGBdx.R;
end;
LX := LX + Ldx;
RX := RX + Rdx;
LRGB.B := LRGB.B + LRGBdy.B;
LRGB.G := LRGB.G + LRGBdy.G;
LRGB.R := LRGB.R + LRGBdy.R;
RRGB.B := RRGB.B + RRGBdy.B;
RRGB.G := RRGB.G + RRGBdy.G;
RRGB.R := RRGB.R + RRGBdy.R;
end;
except
ShowMessage('Exception in GouraudPoly Method');
end;
end;
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