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{
fpGUI - Free Pascal GUI Toolkit
Copyright (C) 2006 - 2010 See the file AUTHORS.txt, included in this
distribution, for details of the copyright.
See the file COPYING.modifiedLGPL, included in this distribution,
for details about redistributing fpGUI.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Description:
A Object Pascal implemenation of Wu Anti-Aliased Lines.
For details about the algorithm have a look at:
http://freespace.virgin.net/hugo.elias/graphics/x_wuline.htm
Here is an implementation in C++
http://www.codeproject.com/gdi/antialias.asp
}
unit fpg_wuline;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, fpg_base, fpg_main;
procedure WuLine(ACanvas: TfpgCanvas; Point1, Point2: TPoint; AColor: TfpgColor);
procedure DrawWuCircle(Canvas: TfpgCanvas; x, y, r: integer; AColor: TfpgColor);
implementation
type
// to get access to Protected fields
TCanvasHack = class(TfpgCanvas);
// Blend a pixel with the current colour
procedure AlphaBlendPixel(ACanvas: TfpgCanvas; X, Y: integer; R, G, B: word; ARatio: Double);
var
LBack, LNew: TRGBTriple;
LMinusRatio: Double;
begin
if (X < 0) or (X > TCanvasHack(ACanvas).FWindow.Width - 1) or (Y < 0) or
(Y > TCanvasHack(ACanvas).FWindow.Height - 1) then
Exit; // clipping
LMinusRatio := 1 - ARatio;
LBack := fpgColorToRGBTriple(ACanvas.Pixels[X, Y]);
LNew.Blue := round(B*ARatio + LBack.Blue*LMinusRatio);
LNew.Green := round(G*ARatio + LBack.Green*LMinusRatio);
LNew.Red := round(R*ARatio + LBack.Red*LMinusRatio);
LNew.Alpha := 255;
ACanvas.Pixels[X, Y] := RGBTripleTofpgColor(LNew);
end;
// Draw a anti-aliased line
procedure WuLine(ACanvas: TfpgCanvas; Point1, Point2: TPoint; AColor: TfpgColor);
var
deltax, deltay, loop, start, finish: integer;
dx, dy, dydx: single; // fractional parts
LR, LG, LB: word;
x1, x2, y1, y2: integer;
begin
x1 := Point1.X;
y1 := Point1.Y;
x2 := Point2.X;
y2 := Point2.Y;
deltax := abs(x2 - x1); // Calculate deltax and deltay for initialisation
deltay := abs(y2 - y1);
if (deltax = 0) or (deltay = 0) then // straight lines
begin
ACanvas.SetColor(AColor);
ACanvas.DrawLine(x1, y1, x2, y2);
Exit; //==>
end;
LR := fpgGetRed(AColor);
LG := fpgGetGreen(AColor);
LB := fpgGetBlue(AColor);
if deltax > deltay then
begin // horizontal or vertical
if y2 > y1 then // determine rise and run
dydx := -(deltay / deltax)
else
dydx := deltay / deltax;
if x2 < x1 then
begin
start := x2; // right to left
finish := x1;
dy := y2;
end
else
begin
start := x1; // left to right
finish := x2;
dy := y1;
dydx := -dydx; // inverse slope
end;
for loop := start to finish do
begin
AlphaBlendPixel(ACanvas, loop, trunc(dy), LR, LG, LB, 1 - frac(dy));
AlphaBlendPixel(ACanvas, loop, trunc(dy) + 1, LR, LG, LB, frac(dy));
dy := dy + dydx; // next point
end;
end
else
begin
if x2 > x1 then // determine rise and run
dydx := -(deltax / deltay)
else
dydx := deltax / deltay;
if y2 < y1 then
begin
start := y2; // right to left
finish := y1;
dx := x2;
end
else
begin
start := y1; // left to right
finish := y2;
dx := x1;
dydx := -dydx; // inverse slope
end;
for loop := start to finish do
begin
AlphaBlendPixel(ACanvas, trunc(dx), loop, LR, LG, LB, 1 - frac(dx));
AlphaBlendPixel(ACanvas, trunc(dx) + 1, loop, LR, LG, LB, frac(dx));
dx := dx + dydx; // next point
end;
end;
end;
// A very basic circle implementation. Not to pretty, but it works.
procedure DrawWuCircle(Canvas: TfpgCanvas; x, y, r: integer; AColor: TfpgColor);
var
x1, y1, x2, y2: integer;
dt: integer;
theta: integer;
begin
theta := 0;
dt := 4;
while theta < 360 do
begin
x1 := round( r*cos(theta*pi/180.0)+x);
y1 := round(-r*sin(theta*pi/180.0)+y);
x2 := round( r*cos((theta+dt)*pi/180.0)+x);
y2 := round(-r*sin((theta+dt)*pi/180.0)+y);
WuLine(Canvas, Point(x1, y1), Point(x2, y2), AColor);
theta := theta + dt;
end;
end;
end.
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