Mega Code Archive
Antialiased line drawer using scanline
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Title: Antialiased line drawer using scanline
Question: How to draw antialiased lines using a TBitmap's scanlines
Answer:
procedure AALine(x1,y1,x2,y2 : single; color : tcolor; bitmap : tbitmap);
function CrossFadeColor(FromColor,ToColor : TColor; Rate : Single) : TColor;
var r,g,b : byte;
begin
r:=Round(GetRValue(FromColor)*Rate+GetRValue(ToColor)*(1-Rate));
g:=Round(GetGValue(FromColor)*Rate+GetGValue(ToColor)*(1-Rate));
b:=Round(GetBValue(FromColor)*Rate+GetBValue(ToColor)*(1-Rate));
Result:=RGB(b,g,r);
end;
type
intarray = array[0..1] of integer;
pintarray = ^intarray;
procedure hpixel(x : single; y : integer);
var FadeRate : single;
begin
FadeRate:=x-trunc(x);
with bitmap do
begin
if (x=0) and (y=0) and (heighty) and (widthx) then
pintarray(bitmap.ScanLine[y])[trunc(x)]:=CrossFadeColor(Color,pintarray(bitmap.ScanLine[y])[trunc(x)],1-FadeRate);
if (trunc(x)+1=0) and (y=0) and (heighty) and (widthtrunc(x)+1) then
pintarray(bitmap.ScanLine[y])[trunc(x)+1]:=CrossFadeColor(Color,pintarray(bitmap.ScanLine[y])[trunc(x)+1],FadeRate);
end;
end;
procedure vpixel(x : integer; y : single);
var FadeRate : single;
begin
FadeRate:=y-trunc(y);
with bitmap do
begin
if (x=0) and (trunc(y)=0) and (heighttrunc(y)) and (widthx) then
pintarray(bitmap.ScanLine[trunc(y)])[x]:=CrossFadeColor(Color,pintarray(bitmap.ScanLine[trunc(y)])[x],1-FadeRate);
if (x=0) and (trunc(y)+1=0) and (heighttrunc(y)+1) and (widthx) then
pintarray(bitmap.ScanLine[trunc(y)+1])[x]:=CrossFadeColor(Color,pintarray(bitmap.ScanLine[trunc(y)+1])[x],FadeRate);
end;
end;
var i : integer;
ly,lx,currentx,currenty,deltax,deltay,l,skipl : single;
begin
if (x1x2) or (y1y2) then
begin
bitmap.PixelFormat:=pf32Bit;
currentx:=x1;
currenty:=y1;
lx:=abs(x2-x1);
ly:=abs(y2-y1);
if lxly then
begin
l:=trunc(lx);
deltay:=(y2-y1)/l;
if x1x2 then
begin
deltax:=-1;
skipl:=(currentx-trunc(currentx));
end else
begin
deltax:=1;
skipl:=1-(currentx-trunc(currentx));
end;
end else
begin
l:=trunc(ly);
deltax:=(x2-x1)/l;
if y1y2 then
begin
deltay:=-1;
skipl:=(currenty-trunc(currenty));
end else
begin
deltay:=1;
skipl:=1-(currenty-trunc(currenty));
end;
end;
currentx:=currentx+deltax*skipl;
currenty:=currenty+deltay*skipl;{}
for i:=1 to trunc(l) do
begin
if lxly then vpixel(trunc(currentx),currenty) else hpixel(currentx,trunc(currenty));
currentx:=currentx+deltax;
currenty:=currenty+deltay;
end;
end;
end;
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