Canvas.LineTo on TImage very SLOW

Hello, I'm trying to make a tool to get the distance from
a point to another in a map (TImage). I click on the map
then a line moves from that first point to wherever the
mouse moves over the map until the next click.
To do so I make a copy of the original bitmap in another
and copy that one to the TImage after every move of the
mouse to repaint the line to the new position.

This works fine on the comp I'm working, AMD K6-650 with a poor S3 4mb card in windows XP PRO; however I tried
the program in a P3 1Ghz gf2mx200 32mb also in Win xp PRO and it was slow as hell, the new line takes ages to repaint; we tried it as well in our laptop, k6 500 or so and same happened, well it was a bit faster.

Any clue what's happening or a better way to do it ?


Some of the code:

procedure TMaps.DistImageMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
if (Button = mbRight) and DistEnabled then
 begin
  // Finish
  DistEnabled:= False;
  DistImage.Canvas.Draw(0,0,DistImgTmp);
  Label51.Caption:= 'Marque un punto inicial con el ratón sobre el mapa.';
  Label52.Caption:= Format('%d km.',[TotalDist]);
  Exit;
 end;
if (not DistEnabled) and (Button = mbLeft) then // Start Straight Lining
 begin
  DistImage.Canvas.Draw(0,0,DistOrig);
  DistImgTmp.Canvas.Draw(0,0,DistImage.Picture.Graphic);
  TotalDist:= 0;
  DistEnabled:= True;
  DistImgX:= x;
  DistImgY:= y;
  Label51.Caption:= 'Marque los puntos consecuentes del recorrido a medir.'+#13#10+
                      'Para finarlizar puse el boton derecho del ratón.';
  DistImage.Canvas.Brush.Color:= clLime;
  DistImage.Canvas.Brush.Style:= bsDiagCross;
  DistImage.Canvas.Pen.Width:= 3;
  DistImage.Canvas.Pen.Color:= clLime;
  DistImage.Canvas.MoveTo(DistImgX, DistImgY);
  Exit;
 end;
if (DistEnabled) and (Button = mbLeft) then // Next Point
 begin
  DistImgTmp.Canvas.Draw(0,0,DistImage.Picture.Graphic);
  DistImgX:= x;
  DistImgY:= y;
  DistImage.Canvas.MoveTo(DistImgX, DistImgY);
  TotalDist:= TotalDist + Trunc(Ex);
 end;
end;

procedure TMaps.DistImageMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
if DistEnabled then
 begin
  DistImage.Canvas.Draw(0,0,DistImgTmp);
  DistImage.Canvas.MoveTo(DistImgX, DistImgY);
  DistImage.Canvas.LineTo(x,y);
  Ex:= (X-DistImgX) * Escala;
  Ex2:= (Y-DistImgY) * Escala;
  Ex:= sqrt(Ex*Ex+Ex2*Ex2);
  Label52.Caption:= Format('%f km.',[TotalDist + Ex]);
  Label52.Repaint;
 end;
end;
menorcanetAsked:
Who is Participating?
 
TOndrejConnect With a Mentor Commented:
Just a very quick demo, Image1.Visible is False.

type
  TForm1 = class(TForm)
    Image1: TImage;
    procedure Form1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure Form1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    procedure Form1MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
  private
    FLine: array[0..1] of TPoint;
    procedure DrawLine;
  public
  end;

procedure TForm1.DrawLine;
begin
  with Canvas do
  begin
    Pen.Color := clWhite;
    Pen.Mode := pmXor;
    with FLine[0] do
      MoveTo(X, Y);
    with FLine[1] do
      LineTo(X, Y);
  end;
end;

procedure TForm1.Form1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  FLine[0] := Point(X, Y);
end;

procedure TForm1.Form1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
  if FLine[0].X <> -1 then
  begin
    if FLine[1].X <> -1 then // erase previous line
      DrawLine;
    FLine[1] := Point(X, Y);
    DrawLine; // draw new line
  end;
end;

procedure TForm1.Form1MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  DrawLine; // erase previous line
  FLine[0] := Point(-1, -1);
  FLine[1] := Point(-1, -1);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  FLine[0] := Point(-1, -1);
  FLine[1] := Point(-1, -1);
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  Canvas.Draw(0, 0, Image1.Picture.Graphic);
end;
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TOndrejCommented:
You're drawing the whole image on every mousemove... <shudder>
How about leaving the image as is, and using a xor pen to draw the line? (first time xor draws the line, second time it erases)
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menorcanetAuthor Commented:
umm, its the first time I'm using the canvas drawing
functions, brushes etc, don't know very well how to
do it properly, could you drop some code ? I can add
more points if needed.

Thanks for your time.
0
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DirkVerdonckCommented:
Redrawing the complete bitmap every time is going to cost a lot in performance.  I don't think you're ever gonna make it work acceptably on a standard machine.

What I would try is the following:  have two canvasses, one with the image in it, and one of exactly the same size directly above it, and set to be transparant.  So when you move the mouse, you don't redraw the bitmap, just clear the upper canvas and draw the line again.

Hope this helps...
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menorcanetAuthor Commented:
Hello, thanks again. I tried the code and it works nicely!
I will learn from it an adapt it to my current code; I
will make a canvas and jpeg (would it be worth the speed
using a bitmap in stead of jpeg?) in memory.

brb
0
 
S_WarriorCommented:
Try to draw the line's on the onPaint event.
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