TImage scanline not draws second time after drawing on Canvas
lazarus / 39-Graphics

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Borneq · 2014-07-12 06:08

I have converted program from Delphi to Lazarus. In Delphi program
works. In Lazarus - control TImage not redraw changes made by
scanlines at second time after drawing on Canvas.
I explain better: I attach source of my program
At start it read samples.dat and fills list. If I click at "trójkąt"
this draw black lines on white canvas, then I press "Piksele" (program
IDE is in Polish, source in English) and OK - Draw Black/Yellow
triangle
Next I click "trójkat 2", it again draw on white canvas. Again I press
"Piksele" and is ERROR: nothing I see. It should draw pixels again.
In Delphi it is was OK.
Maybe some resources not freed/bad initialized?

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howardpc · 2014-07-12 20:32

For FPC/Lazarus you need to wrap the Scanline call in
BeginUpdate/EndUpdate calls thus:

Code: [Select]
uses graphics;

...

procedure TForm1.InsideAllPoints(poly: TPoly);
var
...
begin
...
    begin
       BeginUpdate();
       Line := Scanline[y];
       EndUpdate();
       for x := 0 to ...
       ...
    end;

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Borneq · 2014-07-12 22:41

Each scanline or block of scanlines? BeginUpdate/EndUpdate of which
object? Image.Picture.Bitmap
Very thanks! It Is helps!

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Borneq · 2014-07-13 06:31

Second question: If I choose "trojkat", method stay "simple", on left
I choose "Detale" and press button "Piksele", then appear window "1227
punktów"
If I change list positoin, it draw white small rectangle. There are
two errors:
- rectangle should be red
- previous rectangle should be erased
I draw rectangle in TDetailsForm.DrawPoint i unit Details.pas and
erase in TDetailsForm.ErasePoint
Before drawing I save rectangle to bitmap:
  Bitmap.Canvas.CopyRect(Rect(0,0,DrawW,DrawH),Form1.Image.Canvas,R);
If erase - I try restore from bitmap:
  CopyRect(R, Bitmap.Canvas,Rect(0,0,DrawW,DrawH));
Restoring not works, and not works "Brush.Color:=clRed;"

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howardpc · 2014-07-14 10:06

I'm not exactly sure what DrawPoint/ErasePoint were trying to achieve,
but try this.
Change TDetailsform as follows:
Code: [Select]
  TDetailsForm = class(TForm)
    lvPoints: TListView;
    lvInsideSlopes: TListView;
    lvOutsideSlopes: TListView;
    btnOK: TButton;
    Label1: TLabel;
    Label2: TLabel;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure lvPointsChange(Sender: TObject; Item: TListItem;
      Change: TItemChange);
  private
    ErrPointList: TErrPointList;
    FDrawPointNeeded: boolean;
    FDrawPoint: TPoint;
  public
    procedure Clear;
    procedure CollectErrorPoints(x,y: integer);
    procedure Fill;
    property DrawPointNeeded: boolean read FDrawPointNeeded write
FDrawPointNeeded;
    property DrawPoint: TPoint read FDrawPoint;
  end; 

and move to the public interface
Code: [Select]const
  DrawW=6; DrawH=6;

change TDetailsForm.lvPointsChange as follows:
Code: [Select]begin
  if item.Selected=false then exit;
  if lvPoints_lastSelected=item.Index then exit;
  lvPoints_lastSelected:=item.Index;
  ErrPoint:=Item.Data;
  FDrawPointNeeded:=True;
  FDrawPoint.x:=ErrPoint.x;
  FDrawPoint.y:=ErrPoint.y;
  Form1.Image.Refresh;

  lvInsideSlopes.Clear;
 ... etc.

In DrawUnit add an OnPaint handler for the TImage, and code as
follows:
Code: [Select]procedure TForm1.ImagePaint(Sender: TObject);
var
  img: TImage;

  procedure DrawPoint(aPt: TPoint);
  var
    r: TRect;
  begin
    r:=Rect(aPt.x-DrawW div 2,aPt.y-DrawH div 2,aPt.x+DrawW div
2,aPt.y+DrawH div 2);
    img.Canvas.Brush.Color:=clRed;
    img.Canvas.FillRect(r);
  end;

begin
  img:=Sender as TImage;
  if DetailsForm.DrawPointNeeded then begin
    DrawPoint(DetailsForm.DrawPoint);
    DetailsForm.DrawPointNeeded:=False;
  end;
end;

You'll probably need to adapt all this to achieve exactly what you
want, but it should give you an idea of how to interact with the paint
process at the right moments.

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Borneq · 2014-07-14 12:07

Thanks, this works