[SOLVED] With Sender problem

[Badger]

I am using a TImage canvas to display text and graphics  on the screen. (TextOUt, MoveTo, LineTo, etc). When a user hits the 'Print' button I want to repeat all the code but send it to the printer instead. I tried Copying the Image bitmap to the printer but the text was a bit fuzzy so I had to go back to my original idea and use code for the printer.

Rather than write the code twice I thought I could call a "PutOnPage(Sender:Object)  - either  calling image or printer routine - and just cover the ratio of image resolution to printer resolution with a ratio.

I know sender.canvas is the clue .However, as  I understand it, I have to use the term With Sender as .... or  with sender.canvas do (either printer or TImage.)  this means I would still have to duplicate the code.  Is there a way round this?

[winni]

Hi!

Put all your drawings to the canvas together in one main procedure:

Code: Pascal  [Select][+][-]

1. Procedure TForm1.MainGraph (Can: TCanvas);
2. begin
3. Can.TextOut (x1,y1,'Toast Test Taste');
4. ....
5. ....
6. end;
7.  

After that you only have two different calls:

Code: Pascal  [Select][+][-]

1. MainGraph (Image1.Canvas);
2.  

or

Code: Pascal  [Select][+][-]

1. MainGraph (Printer1.Canvas);
2.  

Or draw it on any component that owns a canvas.

Winni

[Thaddy]

Yes, you can draw on any canvas and subsequently assign that to any other canvas.

[jamie]

The printer's dots per inch is normally much higher than your screen so you'll end up with a small image on a sheet of paper and if you stretch draw it then the image will most likely look a little distorted.

  Depending on how the metrics is setup for the Stretch draw code depends on how the image looks afterwards.

 In windows you can set the stretching to smooth the image so that when you enlarge it you don't get blocking corners and when shrinking will smooth and blend pixels that would otherwise be missing in the image.

  What I would do is write the code block for drawing to the image via a canvas pass and also pass the Pixels Per Pinch value in the call, this way you can scale the size automatically to fix larger Dot per inch canvases.
 
  I do this in a vector drawing display and it works very nicely..

 Write a simple translating function that will return a pixel value from an inch or mm value.

 For example
   TextOut(S(X),S(Y),  your text);

 S(n) is the function that returns the Pixel value plot location using the current DPI settings of the canvas.

[Thaddy]

That technique is called oversampling: dwaing in higher precision, say 4 times and scale it to be smaller, not larger.

[jamie]

Here is a conceptional idea of helping the cause a bit.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4. {$ModeSwitch TypeHelpers}
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     procedure Button1Click(Sender: TObject);
17.   private
18.  
19.   public
20.  
21.   end;
22.  TMyCanvasHelper = Class Helper for TCanvas
23.     Private
24.     Function I(X:Single):Integer;
25.     Public
26.     Class Var DPI:Integer;
27.     Procedure TextOutInch(X,Y:Single;S:String);
28.    end;
29. var
30.   Form1: TForm1;
31.  
32. implementation
33.  
34. {$R *.lfm}
35.  
36.  { TForm1 }
37.  
38.  procedure TForm1.Button1Click(Sender: TObject);
39.  begin
40.    canvas.DPI := Screen.PixelsPerInch; // Normally you would get this from a printer;
41.    Canvas.TextOutInch(1.0, 1.0, 'Test');
42.  end;
43.  Function TMyCanvasHelper.I(X:Single):Integer; Inline;
44.  Begin
45.    Result := Round(X * DPI);
46.  End;
47.  
48.  Procedure TMyCanvasHelper.TextOutInch(X,Y:single;S:String);
49.   begin
50.     Self.TextOut(I(X),I(Y),S);
51.   end;
52. end.
53.  

Help out the TCanvas and give it some more functions that uses Inch scale instead!
 This idea will pave the way to add all the other functions needed so that one can print using inches if they wish, if they want to remain at pixels using the same math then set the DPI to 1 otherwise set it to the Printer canvas DPI or screen or what ever.

[winni]

The resolution is mostly not the problem. And if you rely on the information given by the printer drivers you often run in trouble.

Asking GetDeviceCaps will give you often nonsens.

And the relationship of height and width often differs between the (basic) image, a printer and a preview and an icon.

So what I do is to enhance my above example to

Code: Pascal  [Select][+][-]

1. Procedure TForm1.MainGraph (Can: TCanvas; fx,fy : single);

where fx and fy are the factors for width and height.

I am assuming that the main image is always fx=1 and fy= 1

so fx and fy for a printer are

Code: Pascal  [Select][+][-]

1. fx := Printer.PageWidth/Image1Width;
2. fy := Printer.PageHeight/Image1.height;
3.  

In reality you (most) have to swap PageWidth and PageHeight as an image on the screen is typically landscape and the printer not - but that is a second issue.

And then I only have to do

Code: Pascal  [Select][+][-]

1. Can.TextOut (round (x1*fx), round(y1*fy),'A Text');

Winni

[Badger]

Thanks All
My problem was I was trying to pass the object as the parameter rather than its canvas.