How does OnPaint work?
lazarus / 39-Graphics

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knifemod · 2014-05-31 10:41

Hello,

So i got array BoardConnection[x1,y1,x2,y2] : boolean that says
Coords stored in BoardCoords[x1,y1] are connected with line with
another coords in BoardCoords[x2,y2] if and only if
BoardConnection[x1, y1, x2, y2] = true

More, BoardConnection is declared like this
BoardConnection[1..16,1..16,1..16,1..16] so it's pretty small.
and value true can appear in adjacent cells this is |x1-x2| <= 1 &&
|y1-y2| <= 1 so complexity of one OnPaint call is O(n^2) in this case
n = 16 with some constant, so it's really small number for our
computers.

But there is a problem.
When i put just one true value into BoardConnection table and iterate
over it it indeed finds this value and enters this if statement where
i call Canvas.Line, but Line doesn't appear on the screen. But if i
take out this one value out of if statement then line appear on the
screen.

Here is small part of code to illustrate what i'm talking about :

Code: [Select]procedure TFormGame.tryPainting(x, y, wx, wy : integer);
var c1, c2 : TIndexShape;
begin
  if BoardConnection[x, y, wx, wy] = true then
  begin

       c1 := BoardDotArr[x, y].Circle;
       c2 := BoardDotArr[wx, wy].Circle;

       canvas.pen.width := 5;
       Canvas.pen.color := clred;
       Canvas.line(c1.left + c1.Width div 2,c1.top + c1.Height div 2,
                   c2.left + c2.Width div 2,c2.top + c2.Height div 2);
  end;
end;  
this code doesn't do anything.

but i know i put one value true and got indexes 262,262,302,302 so
this code appears to draw black line, but not red one (one from if
statement), althought if i put ShowMessage into if statement i got
confirmation that program indeed entered this if many many times...
Code: [Select]procedure TFormGame.tryPainting(x, y, wx, wy : integer);
var c1, c2 : TIndexShape;
begin
  Canvas.line(262,262,302,302);
  if BoardConnection[x, y, wx, wy] = true then
  begin

       c1 := BoardDotArr[x, y].Circle;
       c2 := BoardDotArr[wx, wy].Circle;

       canvas.pen.width := 5;
       Canvas.pen.color := clred;
       Canvas.line(c1.left + c1.Width div 2,c1.top + c1.Height div 2,
                   c2.left + c2.Width div 2,c2.top + c2.Height div 2);
  end;
end;

I'd love to get some help on this, cause it really bugs me for many
hours...

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Blaazen · 2014-05-31 10:49

You should say what platform you run: (Win or Linux).
Qt and Carbon don'ŧ allow to paint out of OnPaint method, while Win
and GTK2 allows it.
Also what Canvas you are painting to? Form.Canvas ? Maybe PaintBox is
better choice...

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circular · 2014-05-31 11:01

I would check the coordinates (c1.left + c1.Width div 2,c1.top +
c1.Height div 2, c2.left + c2.Width div 2,c2.top + c2.Height div 2) to
see if they are not out of bounds. You can put them in the
ShowMessage, for example.

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knifemod · 2014-05-31 11:10

Thanks for answers

circular:
They are sure not out of bound, because i use c1.left and c1.top to
draw shapes on the screen and more, i got those coords from
ShowMessage

Blaazen:
I work on windows XP now, but i need to make it work on Linux too.
Yes, by default it's form.canvas. It really buggs me why such thing is
happening.

I'd love to hear some suggestion how to make it work. It obviously
doesn't have to be my way of course. Thank you in advance

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taazz · 2014-05-31 11:17

how is the trypainting method called? where it supposed to paint to ?

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User137 · 2014-05-31 11:26

Quote from: knifemod on May 31, 2014, 01:10:06 pmThey are sure not out
of bound, because i use c1.left and c1.top to draw shapes on the
screen and more, i got those coords from ShowMessage
And what about the Width and Height values?

You said that the black line draws, but not one in the If structure so
it can only be a coordinate problem.

Print out all these values
c1.left + c1.Width div 2
c1.top + c1.Height div 2
c2.left + c2.Width div 2
c2.top + c2.Height div 2

Also comment away the if condition so to see that's not a reason.

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Blaazen · 2014-05-31 11:32

Can you make some basic test like this:
Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
begin
  Canvas.Line(0, 0, Width, Height);
end;It works in Wine but maybe not in Win XP .

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knifemod · 2014-05-31 11:53

Quote from: User137 on May 31, 2014, 01:26:26 pmAnd what about the
Width and Height values?

You said that the black line draws, but not one in the If structure so
it can only be a coordinate problem.
Width and Height values are <= 10
Coordinates is for sure ok, cause when i used drag&drop i used this
formula to join two shapes in OnDragDrop

For second statement see my answer below.

Quote from: taazz on May 31, 2014, 01:17:32 pmhow is the trypainting
method called? where it supposed to paint to ?

Code: [Select]procedure TFormGame.FormPaint(Sender: TObject);
begin
  //painting connections in the board
  MakeConnections;
end; 
function TFormGame.inRange(x, y : integer) : boolean;
begin
  if (x in [1..16]) and (y in [1..16]) then
     inRange := true
  else
     inRange := false;
end;

procedure TFormGame.tryPainting(x, y, wx, wy : integer);
var c1, c2 : TIndexShape;
begin
  //
  if BoardConnection[x, y, wx, wy] = true then
  begin

       c1 := BoardDotArr[x, y].Circle;
       c2 := BoardDotArr[wx, wy].Circle;

       canvas.pen.width := 5;
       Canvas.pen.color := clred;
       FormGame.Canvas.line(262,262,302,302); //ITS IN IF STATEMENT
AND IT DOESN'T WORK EITHER
       FormGame.Canvas.line(c1.left + c1.Width div 2,c1.top +
c1.Height div 2,
                   c2.left + c2.Width div 2,c2.top + c2.Height div 2);
  end;
end;

procedure TFormGame.MakeConnections;
var dx : array[1..3] of integer;
var i, j, di, dj : integer;
begin
    dx[1] := -1;
    dx[2] := 0;
    dx[3] := 1;

    for i := 1 to HeightOfMap do
         for j := 1 to WidthOfMap do
              for di := 1 to 3 do
                   for dj := 1 to 3 do
                   begin
                        if (inRange(i+dx[di],j+dx[dj]) = true) then
                        begin
                           tryPainting(i,j,i+dx[di],j+dx[dj]);
                        end;
                   end;
end;          
That's my whole code for OnPaint, pretty straightforward. Forgive me
if i did some major mistake, still learning. I would appreciate some
help on this one

Edit: I did those connections in OnDragDrop, but when i resize window
or minimize it my connections disappear, so i had to put them into
OnPaint method.

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taazz · 2014-05-31 12:25

I took a close look on the code I do not see a reason not to draw, the
only thing I haven't looked at is
1) the assumption that it draws black lines, it might as well draw
them I don't know.
2) the pen.style I assume is psSolid?
3) there is no other component on the form that hides the drawing.

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knifemod · 2014-05-31 16:00

Thank you guys for your time!
I was missing +1 in one place in the code, it caused access violation,
but it showed up when i tried to join all dots on the map!
Thanks again!