draw an image or a bitmap in memory and modify it in memory

[rabbit_dance]

please describe how to draw an image or a bitmap in memory and modify it in memory and how to put it on the screen

[VTwin]

Have a look here:

https://wiki.lazarus.freepascal.org/Developing_with_Graphics

[rabbit_dance]

thanks, but how to do so under console under such as linux?

[Handoko]

Console? 

Why do you need doing graphics in console mode? I haven't tried but if TBitmap can be used on console mode then there is no difference as doing it in GUI mode, just don't show it on the GUI form.

Below is a demo drawing objects on TBitmap in memory (GUI mode), which with some modifications I believe can be used in console mode:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
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.     btnShow: TButton;
16.     btnCreate: TButton;
17.     btnClear: TButton;
18.     btnWhite: TButton;
19.     btnCircle: TButton;
20.     btnSquare: TButton;
21.     procedure btnCircleClick(Sender: TObject);
22.     procedure btnClearClick(Sender: TObject);
23.     procedure btnCreateClick(Sender: TObject);
24.     procedure btnShowClick(Sender: TObject);
25.     procedure btnSquareClick(Sender: TObject);
26.     procedure btnWhiteClick(Sender: TObject);
27.     procedure FormCreate(Sender: TObject);
28.   private
29.     FBitmap: TBitmap;
30.   end;
31.  
32. var
33.   Form1: TForm1;
34.  
35. implementation
36.  
37. {$R *.lfm}
38.  
39. { TForm1 }
40.  
41. procedure TForm1.FormCreate(Sender: TObject);
42. begin
43.   FBitmap := nil;
44. end;
45.  
46. procedure TForm1.btnCircleClick(Sender: TObject);
47. const
48.   D = 30;
49. var
50.   X, Y: Integer;
51. begin
52.   if not(Assigned(FBitmap)) then
53.   begin
54.     ShowMessage('Please create the bitmap first.');
55.     Exit;
56.   end;
57.   X := Random(FBitmap.Width  - D);
58.   Y := Random(FBitmap.Height - D);
59.   FBitmap.Canvas.Brush.Color := Random($FFFFFF);
60.   FBitmap.Canvas.Ellipse(X, Y, X+D, Y+D);
61. end;
62.  
63. procedure TForm1.btnClearClick(Sender: TObject);
64. begin
65.   if not(Assigned(FBitmap)) then
66.   begin
67.     ShowMessage('Please create the bitmap first.');
68.     Exit;
69.   end;
70.   FBitmap.Canvas.Brush.Color := clBlack;
71.   FBitmap.Canvas.Clear;
72. end;
73.  
74. procedure TForm1.btnShowClick(Sender: TObject);
75. begin
76.   if not(Assigned(FBitmap)) then
77.   begin
78.     ShowMessage('The bitmap has not created yet.');
79.     Exit;
80.   end;
81.   Canvas.Draw(10, 10, FBitmap)
82. end;
83.  
84. procedure TForm1.btnSquareClick(Sender: TObject);
85. const
86.   S = 30;
87. var
88.   X, Y: Integer;
89. begin
90.   if not(Assigned(FBitmap)) then
91.   begin
92.     ShowMessage('Please create the bitmap first.');
93.     Exit;
94.   end;
95.   X := Random(FBitmap.Width  - S);
96.   Y := Random(FBitmap.Height - S);
97.   FBitmap.Canvas.Brush.Color := Random($FFFFFF);
98.   FBitmap.Canvas.Rectangle(X, Y, X+S, Y+S);
99. end;
100.  
101. procedure TForm1.btnWhiteClick(Sender: TObject);
102. begin
103.   if not(Assigned(FBitmap)) then
104.   begin
105.     ShowMessage('Please create the bitmap first.');
106.     Exit;
107.   end;
108.   FBitmap.Canvas.Brush.Color := clWhite;
109.   FBitmap.Canvas.Rectangle(0, 0, FBitmap.Width, FBitmap.Height);
110. end;
111.  
112. procedure TForm1.btnCreateClick(Sender: TObject);
113. begin
114.   if Assigned(FBitmap) then
115.   begin
116.     ShowMessage('The bitmap has been created.');
117.     Exit;
118.   end;
119.   FBitmap := TBitmap.Create;
120.   FBitmap.Height := 100;
121.   FBitmap.Width  := 200;
122. end;
123.  
124. end.

For your information, doing image using TCanvas is slow. If you want to develop a 'real' graphics program (maybe batch editing, watermarking, or resizing) you should use a 'better' graphics library.

https://wiki.lazarus.freepascal.org/Graphics_libraries

[edit]
Oops, I forgot. We should free the FBitmap before exiting the program.

[engkin]

thanks, but how to do so under console under such as linux?

Here is an example.

[rabbit_dance]

thanks, but how to do so under console under such as linux?

Here is an example.

the problem discussed in your post is not same to my problem.
the code in the given example contains unit graphics, which does not contain in rtl and fcl.

[engkin]

You know better what you need. The example gives you a canvas to draw on, that's all.

[engkin]

I just saw your other thread and now I see what you mean.