delphi draw antialiased line
procedure DrawAntialisedLine(Canvas: TCanvas; const AX1, AY1, AX2, AY2: real; const LineColor: TColor);
var
swapped: boolean;
procedure plot(const x, y, c: real);
var
resclr: TColor;
begin
if swapped then
resclr := Canvas.Pixels[round(y), round(x)]
else
resclr := Canvas.Pixels[round(x), round(y)];
resclr := RGB(round(GetRValue(resclr) * (1-c) + GetRValue(LineColor) * c),
round(GetGValue(resclr) * (1-c) + GetGValue(LineColor) * c),
round(GetBValue(resclr) * (1-c) + GetBValue(LineColor) * c));
if swapped then
Canvas.Pixels[round(y), round(x)] := resclr
else
Canvas.Pixels[round(x), round(y)] := resclr;
end;
function rfrac(const x: real): real; inline;
begin
rfrac := 1 - frac(x);
end;
procedure swap(var a, b: real);
var
tmp: real;
begin
tmp := a;
a := b;
b := tmp;
end;
var
x1, x2, y1, y2, dx, dy, gradient, xend, yend, xgap, xpxl1, ypxl1,
xpxl2, ypxl2, intery: real;
x: integer;
begin
x1 := AX1;
x2 := AX2;
y1 := AY1;
y2 := AY2;
dx := x2 - x1;
dy := y2 - y1;
swapped := abs(dx) < abs(dy);
if swapped then
begin
swap(x1, y1);
swap(x2, y2);
swap(dx, dy);
end;
if x2 < x1 then
begin
swap(x1, x2);
swap(y1, y2);
end;
gradient := dy / dx;
xend := round(x1);
yend := y1 + gradient * (xend - x1);
xgap := rfrac(x1 + 0.5);
xpxl1 := xend;
ypxl1 := floor(yend);
plot(xpxl1, ypxl1, rfrac(yend) * xgap);
plot(xpxl1, ypxl1 + 1, frac(yend) * xgap);
intery := yend + gradient;
xend := round(x2);
yend := y2 + gradient * (xend - x2);
xgap := frac(x2 + 0.5);
xpxl2 := xend;
ypxl2 := floor(yend);
plot(xpxl2, ypxl2, rfrac(yend) * xgap);
plot(xpxl2, ypxl2 + 1, frac(yend) * xgap);
for x := round(xpxl1) + 1 to round(xpxl2) - 1 do
begin
plot(x, floor(intery), rfrac(intery));
plot(x, floor(intery) + 1, frac(intery));
intery := intery + gradient;
end;
end;
// Use sample
procedure TForm1.FormCreate(Sender: TObject);
begin
Canvas.Brush.Style := bsSolid;
Canvas.Brush.Color := clWhite;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
begin
Canvas.FillRect(ClientRect);
DrawAntialisedLine(Canvas, Width div 2, Height div 2, X, Y, clBlack);
end;