double loop for a program with the pythagoras

[Handoko]

Step 1 - Remove Useless Items

These should be removed:
- Image2
- Timer2
- Global variables: zwischenspeicher1, zwischenspeicher2, c, c2, j, i, d

Note:
Good programmers usually avoid using global variables, use global variable only when you really need it.

Because variable c has been removed from global scope, now add the variable c it into:
- Procedure TForm1.FormCreate
- Procedure TForm1.Timer1Timer

This code still buggy. But you can download the code for comparison. I also formatted the code to make it more readable.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, Forms, Controls, Graphics, StdCtrls, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     Button2: TButton;
17.     Image1: TImage;
18.     Timer1: TTimer;
19.     procedure Button1Click(Sender: TObject);
20.     procedure Button2Click(Sender: TObject);
21.     procedure FormCreate(Sender: TObject);
22.     procedure Timer1Timer(Sender: TObject);
23.   end;
24.  
25. var
26.   Form1 : TForm1;
27.   mx    : array[1..20] of integer;
28.   my    : array[1..20] of integer;
29.   vx    : array[1..20] of integer;
30.   vy    : array[1..20] of integer;
31.   r     : array[1..20] of integer;
32.  
33. implementation
34.  
35. {$R *.lfm}
36.  
37. { TForm1 }
38.  
39. procedure TForm1.Button1Click(Sender: TObject);
40. begin
41.   Timer1.Enabled := True;
42. end;
43.  
44. procedure TForm1.Button2Click(Sender: TObject);
45. begin
46.   Timer1.Enabled := False;
47. end;
48.  
49. procedure switch (Var a,b:integer);
50. var
51.   zwischenspeicher: Integer;
52. begin
53.   zwischenspeicher := a;
54.   a := b;
55.   b := zwischenspeicher;
56. end;
57.  
58. procedure pythagoras;
59. var
60.   d: Real;
61.   j,i, vx, vy : Integer;
62. begin
63.   for j := 1 to 20 do
64.     for i := 2 to 20 do begin
65.       d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));
66.       if d <= r[j]+r[i]+12 then begin
67.         switch(vx, vx);
68.         switch(vy, vy);
69.       end;
70.     end;
71. end;
72.  
73. procedure TForm1.FormCreate(Sender: TObject);
74. var
75.   c: Integer;
76. begin
77.   Randomize;
78.   Form1.Color    := clPurple;
79.   DoubleBuffered := True;
80.   Timer1.Enabled := False;
81.   for c :=  1 to 20 do begin
82.     r[c] := 20;
83.     mx[c] := Random(Image1.Width);
84.     my[c] := Random(Image1.Height);
85.     vx[c] := Random(10);
86.     vy[c] := Random(10);
87.   end;
88. end;
89.  
90. procedure TForm1.Timer1Timer(Sender: TObject);
91. var
92.   c: Integer;
93. begin
94.   with image1.canvas do begin
95.     for c := 1 to 20 do begin
96.       Pen.Color   := clBlack;
97.       Brush.Color := clBlack;
98.       Ellipse(mx[c]-r[c], my[c]-r[c], mx[c]+r[c], my[c]+r[c]);
99.       mx[c] := mx[c] + vx[c];
100.       my[c] := my[c] + vy[c];
101.       Pen.Color   := clPurple;
102.       Brush.Color := clPurple;
103.       Ellipse(mx[c]-r[c], my[c]-r[c], mx[c]+r[c], my[c]+r[c]);
104.     end;
105.   end;
106.   for c:= 1 to 20 do begin
107.     if my[c]+r[c] >= Image1.Height then vy[c] := -vy[c];
108.     if mx[c]+r[c] >= Image1.Width  then vx[c] := -vx[c];
109.     if my[c]-r[c] < 0              then vy[c] := -vy[c];
110.     if mx[c]-r[c] < 0              then vx[c] := -vx[c];
111.   end;
112. end;
113.  
114. end.

[bradyhartsfield]

Code: Pascal  [Select][+][-]

1. procedure pythagoras;
2.   var d : real;
3.   var j,i, vx, vy : integer;
4. begin
5.   for j := 1 to 20 do
6.     for i := 2 to 20 do begin
7.     d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));
8.     if d <= r[j]+r[i]+12 then begin
9.     vx[j] := -vx[j];
10.     vy[j] := -vy[j];
11.   end;
12.  end;
13. end;

i tried it like this:

Code: Pascal  [Select][+][-]

1. procedure pythagoras;
2. var c,g, vx, vy : integer;
3.     d : real;
4. begin
5.   for c := 1 to 20 do
6.   for g := 2 to 20 do begin
7.     d := sqrt(sqr(mx[c]-mx[g])+sqr(my[c]-my[g]));
8.     if d <= r[c]+r[g]+12 then begin
9.     vx[c] := -vx[c];
10.     vy[c] := -vy[c];
11.   end;
12.  end;
13. end;

here i need to stay that i am using c and g now, because i just created a new project to try different things and i used c and g in that. anyways, if i try it like above there comes the error "Illegal qualifier" and the c from

Code: Pascal  [Select][+][-]

1. vx[c] := -vx[c];

is marked red.

regards
brady

EDIT: i just saw the answer from Handoko, i will look at it now.

[Handoko]

Step 2 - Fixing the Procedure "pythagoras"

These are wrong:
switch(vx, vx);
switch(vy, vy);

It should be:

Code: Pascal  [Select][+][-]

1. switch(vx[j], vx[i]);
2. switch(vy[j], vy[i]);

Don't overlaps the for-loop. The correct for-loop is:
for j := 1 to 20 do
  for i := (j+1) to 20 do
 
Remove the extra +12 from the distance calculation:

Code: Pascal  [Select][+][-]

1. r[j]+r[i]+12

Now remove the useless variables: vx, vy

Code: Pascal  [Select][+][-]

1. procedure pythagoras;
2. var
3.   d: Real;
4.   j,i: Integer;
5. begin
6.   for j := 1 to 20 do
7.     for i := (j+1) to 20 do begin
8.       d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));
9.       if d <= r[j]+r[i] then begin
10.         switch(vx[j], vx[i]);
11.         switch(vy[j], vy[i]);
12.       end;
13.     end;
14. end;

[bradyhartsfield]

Step 1 - Remove Useless Items

These should be removed:
- Image2
- Timer2
- Global variables: zwischenspeicher1, zwischenspeicher2, c, c2, j, i, d

Note:
Good programmers usually avoid using global variables, use global variable only when you really need it.

Because variable c has been removed from global scope, now add the variable c it into:
- Procedure TForm1.FormCreate
- Procedure TForm1.Timer1Timer

This code still buggy. But you can download the code for comparison. I also formatted the code to make it more readable.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, Forms, Controls, Graphics, StdCtrls, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     Button2: TButton;
17.     Image1: TImage;
18.     Timer1: TTimer;
19.     procedure Button1Click(Sender: TObject);
20.     procedure Button2Click(Sender: TObject);
21.     procedure FormCreate(Sender: TObject);
22.     procedure Timer1Timer(Sender: TObject);
23.   end;
24.  
25. var
26.   Form1 : TForm1;
27.   mx    : array[1..20] of integer;
28.   my    : array[1..20] of integer;
29.   vx    : array[1..20] of integer;
30.   vy    : array[1..20] of integer;
31.   r     : array[1..20] of integer;
32.  
33. implementation
34.  
35. {$R *.lfm}
36.  
37. { TForm1 }
38.  
39. procedure TForm1.Button1Click(Sender: TObject);
40. begin
41.   Timer1.Enabled := True;
42. end;
43.  
44. procedure TForm1.Button2Click(Sender: TObject);
45. begin
46.   Timer1.Enabled := False;
47. end;
48.  
49. procedure switch (Var a,b:integer);
50. var
51.   zwischenspeicher: Integer;
52. begin
53.   zwischenspeicher := a;
54.   a := b;
55.   b := zwischenspeicher;
56. end;
57.  
58. procedure pythagoras;
59. var
60.   d: Real;
61.   j,i, vx, vy : Integer;
62. begin
63.   for j := 1 to 20 do
64.     for i := 2 to 20 do begin
65.       d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));
66.       if d <= r[j]+r[i]+12 then begin
67.         switch(vx, vx);
68.         switch(vy, vy);
69.       end;
70.     end;
71. end;
72.  
73. procedure TForm1.FormCreate(Sender: TObject);
74. var
75.   c: Integer;
76. begin
77.   Randomize;
78.   Form1.Color    := clPurple;
79.   DoubleBuffered := True;
80.   Timer1.Enabled := False;
81.   for c :=  1 to 20 do begin
82.     r[c] := 20;
83.     mx[c] := Random(Image1.Width);
84.     my[c] := Random(Image1.Height);
85.     vx[c] := Random(10);
86.     vy[c] := Random(10);
87.   end;
88. end;
89.  
90. procedure TForm1.Timer1Timer(Sender: TObject);
91. var
92.   c: Integer;
93. begin
94.   with image1.canvas do begin
95.     for c := 1 to 20 do begin
96.       Pen.Color   := clBlack;
97.       Brush.Color := clBlack;
98.       Ellipse(mx[c]-r[c], my[c]-r[c], mx[c]+r[c], my[c]+r[c]);
99.       mx[c] := mx[c] + vx[c];
100.       my[c] := my[c] + vy[c];
101.       Pen.Color   := clPurple;
102.       Brush.Color := clPurple;
103.       Ellipse(mx[c]-r[c], my[c]-r[c], mx[c]+r[c], my[c]+r[c]);
104.     end;
105.   end;
106.   for c:= 1 to 20 do begin
107.     if my[c]+r[c] >= Image1.Height then vy[c] := -vy[c];
108.     if mx[c]+r[c] >= Image1.Width  then vx[c] := -vx[c];
109.     if my[c]-r[c] < 0              then vy[c] := -vy[c];
110.     if mx[c]-r[c] < 0              then vx[c] := -vx[c];
111.   end;
112. end;
113.  
114. end.

Okay, i did that, i have football training now, will be online in about two and a half hours.
Thank you for helping!

regards
brady

[Handoko]

Step 3 - Fix Procedure Timer1Timer

You have procedure pythagoras for calculating and doing the bouncing but you forgot to put it in Timer1Timer. So put it at the very beginning of TForm1.Timer1Timer.

I saw you draw a black circle to clear the old circle position. It is very wrong for doing animations especially games. It may work (sometimes) but it usually has bad effect. On your case, I can clearly see some black shadow appears on wrong circles (because you did not do z-order calculation)

The solution is to clear the whole screen before start painting the other things:
Pen.Color   := clBlack;
Brush.Color := clBlack;
Clear;

Code: Pascal  [Select][+][-]

1. procedure TForm1.Timer1Timer(Sender: TObject);
2. var
3.   c: Integer;
4. begin
5.   pythagoras;
6.   with image1.canvas do begin
7.     Pen.Color   := clBlack;
8.     Brush.Color := clBlack;
9.     Clear;
10.     for c := 1 to 20 do begin
11.       mx[c] := mx[c] + vx[c];
12.       my[c] := my[c] + vy[c];
13.       Pen.Color   := clPurple;
14.       Brush.Color := clPurple;
15.       Ellipse(mx[c]-r[c], my[c]-r[c], mx[c]+r[c], my[c]+r[c]);
16.     end;
17.   end;
18.   for c:= 1 to 20 do begin
19.     if my[c]+r[c] >= Image1.Height then vy[c] := -vy[c];
20.     if mx[c]+r[c] >= Image1.Width  then vx[c] := -vx[c];
21.     if my[c]-r[c] < 0              then vy[c] := -vy[c];
22.     if mx[c]-r[c] < 0              then vx[c] := -vx[c];
23.   end;
24. end;

[Handoko]

Step 4 - Some Minor Improvements

Set anchoring for the image and resize the form, add these code into TFrom1.FormCreate:
Image1.Anchors := [akTop, akLeft, akRight, akBottom];
Width  := 800;
Height := 600;

In your Timer1Timer, you can merge to those 2 for-loops together:
for i := 1 to 20 do begin         

I saw you use variable c for looping. Usually programmers use i (and then j, k, ...). So change all those variables' names. By doing so, your code will look like written by a pro.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, Forms, Controls, Graphics, StdCtrls, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     Button2: TButton;
17.     Image1: TImage;
18.     Timer1: TTimer;
19.     procedure Button1Click(Sender: TObject);
20.     procedure Button2Click(Sender: TObject);
21.     procedure FormCreate(Sender: TObject);
22.     procedure Timer1Timer(Sender: TObject);
23.   end;
24.  
25. var
26.   Form1 : TForm1;
27.   mx    : array[1..20] of Integer;
28.   my    : array[1..20] of Integer;
29.   vx    : array[1..20] of Integer;
30.   vy    : array[1..20] of Integer;
31.   r     : array[1..20] of Integer;
32.  
33. implementation
34.  
35. {$R *.lfm}
36.  
37. { TForm1 }
38.  
39. procedure TForm1.Button1Click(Sender: TObject);
40. begin
41.   Timer1.Enabled := True;
42. end;
43.  
44. procedure TForm1.Button2Click(Sender: TObject);
45. begin
46.   Timer1.Enabled := False;
47. end;
48.  
49. procedure switch (var a, b: Integer);
50. var
51.   zwischenspeicher: Integer;
52. begin
53.   zwischenspeicher := a;
54.   a := b;
55.   b := zwischenspeicher;
56. end;
57.  
58. procedure pythagoras;
59. var
60.   d: Real;
61.   i, j: Integer;
62. begin
63.   for i := 1 to 20 do
64.     for j := (i+1) to 20 do begin
65.       d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));
66.       if d <= r[i]+r[j] then begin
67.         switch(vx[i], vx[j]);
68.         switch(vy[i], vy[j]);
69.       end;
70.     end;
71. end;
72.  
73. procedure TForm1.FormCreate(Sender: TObject);
74. var
75.   i: Integer;
76. begin
77.   Randomize;
78.   Image1.Anchors := [akTop, akLeft, akRight, akBottom];
79.   Width  := 800;
80.   Height := 600;
81.   Color  := clPurple;
82.   DoubleBuffered := True;
83.   Timer1.Enabled := False;
84.   for i :=  1 to 20 do begin
85.     r[i] := 20;
86.     mx[i] := Random(Image1.Width);
87.     my[i] := Random(Image1.Height);
88.     vx[i] := Random(10);
89.     vy[i] := Random(10);
90.   end;
91. end;
92.  
93. procedure TForm1.Timer1Timer(Sender: TObject);
94. var
95.   i: Integer;
96. begin
97.   pythagoras;
98.   with image1.canvas do begin
99.     Pen.Color   := clBlack;
100.     Brush.Color := clBlack;
101.     Clear;
102.     for i := 1 to 20 do begin
103.       mx[i] := mx[i] + vx[i];
104.       my[i] := my[i] + vy[i];
105.       if my[i]+r[i] >= Image1.Height then vy[i] := -vy[i];
106.       if mx[i]+r[i] >= Image1.Width  then vx[i] := -vx[i];
107.       if my[i]-r[i] < 0              then vy[i] := -vy[i];
108.       if mx[i]-r[i] < 0              then vx[i] := -vx[i];
109.       Pen.Color   := clPurple;
110.       Brush.Color := clPurple;
111.       Ellipse(mx[i]-r[i], my[i]-r[i], mx[i]+r[i], my[i]+r[i]);
112.     end;
113.   end;
114. end;
115.  
116. end.

[Handoko]

Now, the code should work like what you want.

But, there still 2 serious bugs:
- Balls sticking together
- Ball sticking at the edge

Well I know how to solve the issues above. I ever wrote Arcanoid and I got these issues too. But if I don't think you're now ready for it, so I think it is enough here now.

[molly]

Thank you Handoko !

I think the first order of business was for TS to get some  moving balls on his form. Now TS is able to spot the inaccuracies and think on how to address those.

@TS:
Code can still be improved a little (without directly addressing remaining issues), but you probably have (other) restrictions that prevent form doing so.

One thing you can address though is making use of globals (yes, now it is allowed  ) to define the number of balls for easy customization or as another example the max radius.

Also when i read this:

Code: [Select]

    mx[i] := Random(Image1.Width);
    my[i] := Random(Image1.Height);

Then ask yourself if that is correct. A picture tells more than a thousand words, so you will see soon enough what is wrong with that 

edit: addressing the right person.

[Handoko]

Did you mean it should be:

Code: Pascal  [Select][+][-]

1. mx[i] := Random(Image1.Width - 2*radius) + radius;
2. my[i] := Random(Image1.Height - 2*radius) + radius;

And there was a bug in my code:
The Image1's size right after the form expanded does not has accurate values because the form has not 'actually' created so the calculation isn't accurate.

[molly]

Crêpes Suzette 

I should have been more careful in my post. those where meant for TS, not you Handoko 

But, yes that is exactly what i meant 

[bradyhartsfield]

Hey,

thanks for all your help!

Now i have one more question:

Set anchoring for the image and resize the form, add these code into TFrom1.FormCreate:
Image1.Anchors := [akTop, akLeft, akRight, akBottom];
Width  := 800;
Height := 600;

for what is that? because i dont just want to copy but to understand why i am doing things.

regards
Nick

[Handoko]

Set the width and height of the form. The anchors is to set the image to automatic grow larger or smaller if its parent (the form) resized.

[bradyhartsfield]

Hey,

ah okay, my program is now working! thank you all for your help and especially handoko for that step by step tutorial.

regards,
brady

[Kays]

[…]

Code: Pascal  [Select][+][-]

1. d := sqrt(sqr(mx[j]-mx[i])+sqr(my[j]-my[i]));

FYI, you can shorten/simplify that expression with Math.hypot to

Code: Pascal  [Select][+][-]

1. d := hypot(mx[j]-mx[i], my[j]-my[i]);