SDL2 drag and drop image [SOLVED]

[Pe3s]

Hello, I'm writing a program that wants to create drag and drop functionality.
When compiling there is an error unit1.pas(124,45) Error: Syntax error, "identifier" expected but "FILE" found.
Could I ask for help in solving the problem?

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ComCtrls, ExtCtrls,
9.   StdCtrls, SDL2, SDL2_image, Math;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     OpenDialog1: TOpenDialog;
18.     Panel1: TPanel;
19.     Panel2: TPanel;
20.     StatusBar1: TStatusBar;
21.     procedure Button1Click(Sender: TObject);
22.     procedure FormDestroy(Sender: TObject);
23.     procedure FormResize(Sender: TObject);
24.     procedure FormShow(Sender: TObject);
25.     procedure Panel1Paint(Sender: TObject);
26.   private
27.       SDLWindow: PSDL_Window;
28.       SDLRenderer: PSDL_Renderer;
29.       CurrentTexture: PSDL_Texture;
30.       procedure InitializeSDL;
31.       procedure ShutdownSDL;
32.       procedure LoadAndDisplayImage(const FileName: string);
33.       procedure RenderImage;
34.       procedure HandleDropEvent(const FileName: string);
35.       procedure HandleSDLEvents;
36.  
37.   public
38.  
39.   end;
40.  
41. var
42.   Form1: TForm1;
43.  
44. implementation
45.  
46. {$R *.lfm}
47.  
48. { TForm1 }
49.  
50. procedure TForm1.InitializeSDL;
51. begin
52.   if SDL_Init(SDL_INIT_VIDEO) < 0 then
53.     raise Exception.Create('Nie udało się zainicjować SDL: ' + SDL_GetError);
54.  
55.   SDLWindow := SDL_CreateWindowFrom(Pointer(Panel1.Handle));
56.   if SDLWindow = nil then
57.     raise Exception.Create('Nie udało się utworzyć okna SDL: ' + SDL_GetError);
58.  
59.   SDLRenderer := SDL_CreateRenderer(sdlWindow, -1, SDL_RENDERER_ACCELERATED or SDL_RENDERER_PRESENTVSYNC);;
60.   if SDLRenderer = nil then
61.     raise Exception.Create('Nie można utworzyć renderowania SDL: ' + SDL_GetError);
62.  
63.      // Enable the drag-and-drop feature
64.   SDL_SetWindowGrab(SDLWindow, SDL_TRUE);
65. end;
66.  
67. procedure TForm1.ShutdownSDL;
68. begin
69.    if CurrentTexture <> nil then
70.     SDL_DestroyTexture(CurrentTexture);
71.   if SDLRenderer <> nil then
72.     SDL_DestroyRenderer(SDLRenderer);
73.   if SDLWindow <> nil then
74.     SDL_DestroyWindow(SDLWindow);
75.   IMG_Quit;
76.   SDL_Quit;
77. end;
78.  
79. procedure TForm1.RenderImage;
80. var
81.   DstRect: TSDL_Rect;
82.   ImgWidth, ImgHeight, PanelWidth, PanelHeight: Integer;
83.   AspectRatio: Double;
84. begin
85.   if CurrentTexture = nil then Exit;
86.  
87.   // Get image dimensions
88.   SDL_QueryTexture(CurrentTexture, nil, nil, @ImgWidth, @ImgHeight);
89.  
90.   // Get panel dimensions
91.   PanelWidth := Panel1.Width;
92.   PanelHeight := Panel1.Height;
93.  
94.   // Calculate aspect ratio to fit the image proportionally
95.   AspectRatio := Min(PanelWidth / ImgWidth, PanelHeight / ImgHeight);
96.  
97.   DstRect.w := Round(ImgWidth * AspectRatio);
98.   DstRect.h := Round(ImgHeight * AspectRatio);
99.   DstRect.x := (PanelWidth - DstRect.w) div 2;
100.   DstRect.y := (PanelHeight - DstRect.h) div 2;
101.  
102.   StatusBar1.Panels[0].Text:= IntToStr(ImgWidth) +'x' + inttostr(ImgHeight);
103.  
104.   // Render the image
105.   SDL_RenderClear(SDLRenderer);
106.   SDL_RenderCopy(SDLRenderer, CurrentTexture, nil, @DstRect);
107.   SDL_RenderPresent(SDLRenderer);
108. end;
109.  
110. procedure TForm1.HandleDropEvent(const FileName: string);
111. begin
112.   LoadAndDisplayImage(FileName);
113. end;
114.  
115. procedure TForm1.HandleSDLEvents;
116. var
117.   Event: TSDL_Event;
118. begin
119.   while SDL_PollEvent(@Event) <> 0 do
120.   begin
121.     case Event.type_ of
122.       SDL_DROPFILE:
123.         begin
124.           HandleDropEvent(string(Event.drop.file));
125.           SDL_free(Pointer(Event.drop.file)); // Clean up the file name string
126.         end;
127.       SDL_QUIT:
128.         Close; // Handle quitting the application
129.     end;
130.   end;
131. end;
132.  
133. procedure TForm1.LoadAndDisplayImage(const FileName: string);
134. begin
135.    // Clean up the old texture if it exists
136.   if CurrentTexture <> nil then
137.     SDL_DestroyTexture(CurrentTexture);
138.  
139.   // Load the new image as a texture
140.   CurrentTexture := IMG_LoadTexture(SDLRenderer, PChar(FileName));
141.   if CurrentTexture = nil then
142.     raise Exception.Create('Nie udało się wczytać tekstury: ' + IMG_GetError);
143.  
144.   // Render the image to fit the new size
145.   RenderImage;
146. end;
147.  
148. procedure TForm1.FormShow(Sender: TObject);
149. begin
150.    InitializeSDL;
151. end;
152.  
153. procedure TForm1.Panel1Paint(Sender: TObject);
154. begin
155.   // Draw a red rectangle (example)
156.   SDL_SetRenderDrawColor(sdlRenderer, 0, 0, 0, 255);
157.   SDL_RenderFillRect(sdlRenderer, nil); // Full screen fill
158.   SDL_RenderPresent(sdlRenderer);
159.  
160.    RenderImage;
161. end;
162.  
163. procedure TForm1.FormDestroy(Sender: TObject);
164. begin
165.   ShutdownSDL;
166. end;
167.  
168. procedure TForm1.Button1Click(Sender: TObject);
169. begin
170.   if OpenDialog1.Execute then
171.     begin
172.       LoadAndDisplayImage(OpenDialog1.FileName);
173.     end;
174. end;
175.  
176. procedure TForm1.FormResize(Sender: TObject);
177. begin
178.   RenderImage;
179. end;
180.  
181.  
182. end.
183.  
184.  

Regards

[korba812]

"file" is reserved word in pascal. To use a reserved word as an identifier precede it with "&".

Code: Pascal  [Select][+][-]

1. HandleDropEvent(string(Event.drop.&file));

[Pe3s]

I corrected the code but
unfortunately it doesn't work
maybe the sdl window doesn't support file dropping?

Pascal headers downloaded
https://github.com/ev1313/Pascal-SDL-2-Headers

Code: Pascal  [Select][+][-]

1. procedure TForm1.HandleSDLEvents;
2. var
3.   Event: TSDL_Event;
4. begin
5.   while SDL_PollEvent(@Event) <> 0 do
6.   begin
7.     case Event.type_ of
8.       SDL_DROPFILE:
9.         begin
10.           HandleDropEvent(string(Event.drop.&file));
11.           SDL_free(Pointer(Event.drop.&file)); // Clean up the file name string
12.         end;
13.       SDL_QUIT:
14.         Close; // Handle quitting the application
15.     end;
16.   end;
17. end;        
18.  

Code: Pascal  [Select][+][-]

1. unit1.pas(125,45) Error: identifier idents no member "file"
2. unit1.pas(126,39) Error: identifier idents no member "file"
3. unit1.pas(128,15) Error: Constant and CASE types do not match
4. unit1.pas(128,15) Error: Constant Expression expected

[korba812]

Looking at the sources you provided, this field is named "_file":
https://github.com/ev1313/Pascal-SDL-2-Headers/blob/201a767368020183b9964983d1c57ac4bd6a16fd/sdlevents.inc#L438

[Pe3s]

I changed it but now there is an error SDL_QUIT:

and it doesn't load the image

The code appears to be correct

I would like to learn SDL and drag and drop

Code: Pascal  [Select][+][-]

1.  
2. unit1.pas(132,17) Error: Constant and CASE types do not match
3. unit1.pas(132,17) Error: Constant Expression expected
4.  
5.  

Code: Pascal  [Select][+][-]

1. var
2.   Event: TSDL_Event;
3. begin
4.   while SDL_PollEvent(@Event) <> 0 do
5.   begin
6.     case Event.type_ of
7.       SDL_DROPFILE:
8.         begin
9.           HandleDropEvent(string(Event.drop._file));
10.           SDL_free(Pointer(Event.drop._file)); // Clean up the file name string
11.         end;
12.       SDL_QUIT:
13.         Close; // Handle quitting the application
14.     end;
15.   end;
16. end;            

[korba812]

Again looking at code I conclude that you should use constant "SDL_QUITEV" instead of "SDL_QUIT":
https://github.com/ev1313/Pascal-SDL-2-Headers/blob/201a767368020183b9964983d1c57ac4bd6a16fd/sdlevents.inc#L517C7-L517C17

[Pe3s]

How should I improve the procedure to make dropping files work, because when I drop a file nothing happens.

[Pe3s]

I corrected the code but
drag and drop doesn't work, it doesn't open the image when it is dropped on the window.

What am I doing wrong that this function doesn't work?

Allow drop files does nothing

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ComCtrls, ExtCtrls,
9.   StdCtrls, SDL2, SDL2_image, Math;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     OpenDialog1: TOpenDialog;
18.     Panel1: TPanel;
19.     Panel2: TPanel;
20.     StatusBar1: TStatusBar;
21.     procedure Button1Click(Sender: TObject);
22.     procedure FormDestroy(Sender: TObject);
23.     procedure FormResize(Sender: TObject);
24.     procedure FormShow(Sender: TObject);
25.     procedure Panel1Paint(Sender: TObject);
26.   private
27.       SDLWindow: PSDL_Window;
28.       SDLRenderer: PSDL_Renderer;
29.       CurrentTexture: PSDL_Texture;
30.       procedure InitializeSDL;
31.       procedure ShutdownSDL;
32.       procedure LoadAndDisplayImage(const FileName: string);
33.       procedure RenderImage;
34.       procedure HandleDropEvent(const FilePath: string);
35.       procedure ProcessSDLEvents;
36.  
37.   public
38.  
39.   end;
40.  
41. var
42.   Form1: TForm1;
43.    SDLEvent: TSDL_Event;
44.  
45. implementation
46.  
47. {$R *.lfm}
48.  
49. { TForm1 }
50.  
51. procedure TForm1.InitializeSDL;
52. begin
53.   if SDL_Init(SDL_INIT_VIDEO) < 0 then
54.     raise Exception.Create('Unable to initialize SDL: ' + SDL_GetError);
55.  
56.   // Ensure Panel1.Handle is correctly cast to a pointer
57.   SDLWindow := SDL_CreateWindowFrom(Pointer(Panel1.Handle));
58.   if SDLWindow = nil then
59.     raise Exception.Create('Unable to create SDL window: ' + SDL_GetError);
60.  
61.   // Create the renderer
62.   SDLRenderer := SDL_CreateRenderer(SDLWindow, -1, SDL_RENDERER_ACCELERATED or SDL_RENDERER_PRESENTVSYNC);
63.   if SDLRenderer = nil then
64.     raise Exception.Create('Unable to create SDL renderer: ' + SDL_GetError);
65.  
66.   // Enable SDL's drop events
67.   SDL_EventState(SDL_DROPFILE, SDL_ENABLE);
68. end;
69.  
70. procedure TForm1.ShutdownSDL;
71. begin
72.    if CurrentTexture <> nil then
73.     SDL_DestroyTexture(CurrentTexture);
74.   if SDLRenderer <> nil then
75.     SDL_DestroyRenderer(SDLRenderer);
76.   if SDLWindow <> nil then
77.     SDL_DestroyWindow(SDLWindow);
78.   IMG_Quit;
79.   SDL_Quit;
80. end;
81.  
82. procedure TForm1.RenderImage;
83. var
84.   DstRect: TSDL_Rect;
85.   ImgWidth, ImgHeight, PanelWidth, PanelHeight: Integer;
86.   AspectRatio: Double;
87. begin
88.   if CurrentTexture = nil then Exit;
89.  
90.   // Get image dimensions
91.   SDL_QueryTexture(CurrentTexture, nil, nil, @ImgWidth, @ImgHeight);
92.  
93.   // Get panel dimensions
94.   PanelWidth := Panel1.Width;
95.   PanelHeight := Panel1.Height;
96.  
97.   // Calculate aspect ratio to fit the image proportionally
98.   AspectRatio := Min(PanelWidth / ImgWidth, PanelHeight / ImgHeight);
99.  
100.   DstRect.w := Round(ImgWidth * AspectRatio);
101.   DstRect.h := Round(ImgHeight * AspectRatio);
102.   DstRect.x := (PanelWidth - DstRect.w) div 2;
103.   DstRect.y := (PanelHeight - DstRect.h) div 2;
104.  
105.   StatusBar1.Panels[0].Text:= IntToStr(ImgWidth) +'x' + inttostr(ImgHeight);
106.  
107.   // Render the image
108.   SDL_RenderClear(SDLRenderer);
109.   SDL_RenderCopy(SDLRenderer, CurrentTexture, nil, @DstRect);
110.   SDL_RenderPresent(SDLRenderer);
111. end;
112.  
113. procedure TForm1.HandleDropEvent(const FilePath: string);
114. begin
115.   // Load and display the dropped image file
116.   if FileExists(FilePath) then
117.   begin
118.     LoadAndDisplayImage(FilePath);
119.     Form1.Caption := 'Loaded: ' + ExtractFileName(FilePath);
120.   end
121.   else
122.     ShowMessage('Invalid file dropped: ' + FilePath);
123. end;
124.  
125. procedure TForm1.ProcessSDLEvents;
126. begin
127.   while SDL_PollEvent(@SDLEvent) <> 0 do
128.   begin
129.     case SDLEvent.type_ of
130.       SDL_DROPFILE:
131.         begin
132.           HandleDropEvent(SDLEvent.drop._file);
133.           SDL_free(SDLEvent.drop._file); // Free the file path allocated by SDL
134.         end;
135.       SDL_QUITEV:
136.         begin
137.           Close;
138.         end;
139.     end;
140.   end;
141. end;
142.  
143. procedure TForm1.LoadAndDisplayImage(const FileName: string);
144. begin
145.    // Clean up the old texture if it exists
146.   if CurrentTexture <> nil then
147.     SDL_DestroyTexture(CurrentTexture);
148.  
149.   // Load the new image as a texture
150.   CurrentTexture := IMG_LoadTexture(SDLRenderer, PChar(FileName));
151.   if CurrentTexture = nil then
152.     raise Exception.Create('Nie udało się wczytać tekstury: ' + IMG_GetError);
153.  
154.   // Render the image to fit the new size
155.   RenderImage;
156. end;
157.  
158. procedure TForm1.FormShow(Sender: TObject);
159. begin
160.    InitializeSDL;
161.  
162. end;
163.  
164. procedure TForm1.Panel1Paint(Sender: TObject);
165. begin
166.   // Draw a red rectangle (example)
167.   SDL_SetRenderDrawColor(sdlRenderer, 0, 0, 0, 255);
168.   SDL_RenderFillRect(sdlRenderer, nil); // Full screen fill
169.   SDL_RenderPresent(sdlRenderer);
170.  
171.    RenderImage;
172. end;
173.  
174. procedure TForm1.FormDestroy(Sender: TObject);
175. begin
176.   ShutdownSDL;
177. end;
178.  
179. procedure TForm1.Button1Click(Sender: TObject);
180. begin
181.   if OpenDialog1.Execute then
182.     begin
183.       LoadAndDisplayImage(OpenDialog1.FileName);
184.     end;
185. end;
186.  
187. procedure TForm1.FormResize(Sender: TObject);
188. begin
189.  
190.   RenderImage;
191. end;
192.  
193.  
194. end.
195.  
196.  

[TRon]

What am I doing wrong that this function doesn't work?

It has been a while when working with SDL but let's give it a try 

The concept of what you are trying to do does not compute.

SDL events are processed inside a SDL event loop. GUI events are processed inside the GUI message-loop. These two conflict. In fact, the example-code never actually processes the SDL events.

Either use the drag and drop functionality of Lazarus or change the concept as a whole.

[Pe3s]

The drag and drop function from Lazarus does not work from the SDL window.

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormDropFiles(Sender: TObject; const FileNames: array of string);
2. var
3.   i: Integer;
4. begin
5.   for i := Low(FileNames) to High(FileNames) do
6.      LoadAndDisplayImage(FileNames[i]);
7. end;
8.  

[Pe3s]

How can I combine sdl and lcl so that the drop function also works with the sdl window

[TRon]

The drag and drop function from Lazarus does not work from the SDL window.

I am confused about what you meant by that. Are you trying to drag from the sdl window to the lazarus form or something like that perhaps ?

The hist that I got from your original code is that you want to be able to drag files from the OS and drop to your SDL window, in which case Lazarus LCL should take care of the drop and in the event handler you do whatever you do with the dropped file name (instead of SDL handling the event).

How can I combine sdl and lcl so that the drop function also works with the sdl window

As described above. It is either that or translate either all(*) SDL events to LCL or all(*) LCL events to SDL. Neither one is something that is easily realized.

(*) with all I mean all events that you are interested in and/or need to take care of.

That is why I wrote the concept that you are using in your approach as per your example does not compute as it would require two event loops to be running parallel. In theory that is solvable with running f.e. your SDL event loop inside a thread but as per your example that  would (only) complicate matters further.

How you would need to solve the issue depends entirely on your end-goal which also means that you need to decide whether you want LCL or SDL to handle things. Perhaps you could have a look at the Lazarus GL controls and how things are solved there.

Unfortunately I am unable to provide details because I'm on Linux and passing a LCL handle to SDL using GTK does not compute (and the LCL-foo seem to fail me atm).

[Pe3s]

This sdl code should handle file dropping.

Code: Pascal  [Select][+][-]

1. procedure TForm1.HandleSDLEvents;
2. var
3.   Event: TSDL_Event;
4. begin
5.   while SDL_PollEvent(@Event) <> 0 do
6.   begin
7.     case Event.type_ of
8.       SDL_DROPFILE:
9.         begin
10.           HandleDropEvent(string(Event.drop.file));
11.           SDL_free(Pointer(Event.drop.file)); // Clean up the file name string
12.         end;
13.       SDL_QUIT:
14.         Close; // Handle quitting the application
15.     end;
16.   end;
17. end;
18.  

[Seenkao]

How can I combine sdl and lcl so that the drop function also works with the sdl window

Что именно вы хотите переместить?

1. Если вы с помощью SDL создали графическую область (context) в одной форме и хотите переместить на другой контекст, созданный на другой форме, то это делается только вручную. Если только сам SDL не предоставляет возможностей копирования данных из одного контекста в другой.
2. Если вы хотите скопировать из созданного контекста на одной форме, в другую LCL-форму, то это так же придётся делать вручную.
3. Если вы хотите что-то скопировать из одной формы в другую, то тут, на форуме, вам смогут помочь.

--------------------------------------------------------
Google translate:
What exactly do you want to move?

1. If you created a graphic area (context) in one form using SDL and want to move it to another context created on another form, then this can only be done manually. Unless SDL itself provides the ability to copy data from one context to another.
2. If you want to copy from a created context on one form to another LCL form, then this will also have to be done manually.
3. If you want to copy something from one form to another, then here on the forum they can help you.

[Pe3s]

I want to make it so that the file can be dragged and dropped onto the SDL window to open the file.