SDL2 drag and drop image [SOLVED]
lazarus / 39-Graphics

----------------------------------------------------------------------
Pe3s · 2024-11-20 22:32

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, ComCtrls, ExtCtrls,  StdCtrls, SDL2,
SDL2_image, Math; type   { TForm1 }   TForm1 = class(TForm)   
Button1: TButton;    OpenDialog1: TOpenDialog;    Panel1: TPanel;   
Panel2: TPanel;    StatusBar1: TStatusBar;    procedure
Button1Click(Sender: TObject);    procedure FormDestroy(Sender:
TObject);    procedure FormResize(Sender: TObject);    procedure
FormShow(Sender: TObject);    procedure Panel1Paint(Sender: TObject); 
private      SDLWindow: PSDL_Window;      SDLRenderer: PSDL_Renderer; 
    CurrentTexture: PSDL_Texture;      procedure InitializeSDL;     
procedure ShutdownSDL;      procedure LoadAndDisplayImage(const
FileName: string);      procedure RenderImage;      procedure
HandleDropEvent(const FileName: string);      procedure
HandleSDLEvents;   public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure
TForm1.InitializeSDL;begin  if SDL_Init(SDL_INIT_VIDEO) < 0 then   
raise Exception.Create('Nie udało się zainicjować SDL: ' +
SDL_GetError);   SDLWindow :=
SDL_CreateWindowFrom(Pointer(Panel1.Handle));  if SDLWindow = nil
then    raise Exception.Create('Nie udało się utworzyć okna SDL: ' +
SDL_GetError);   SDLRenderer := SDL_CreateRenderer(sdlWindow, -1,
SDL_RENDERER_ACCELERATED or SDL_RENDERER_PRESENTVSYNC);;  if
SDLRenderer = nil then    raise Exception.Create('Nie można utworzyć
renderowania SDL: ' + SDL_GetError);      // Enable the drag-and-drop
feature  SDL_SetWindowGrab(SDLWindow, SDL_TRUE);end; procedure
TForm1.ShutdownSDL;begin   if CurrentTexture <> nil then   
SDL_DestroyTexture(CurrentTexture);  if SDLRenderer <> nil then   
SDL_DestroyRenderer(SDLRenderer);  if SDLWindow <> nil then   
SDL_DestroyWindow(SDLWindow);  IMG_Quit;  SDL_Quit;end; procedure
TForm1.RenderImage;var  DstRect: TSDL_Rect;  ImgWidth, ImgHeight,
PanelWidth, PanelHeight: Integer;  AspectRatio: Double;begin  if
CurrentTexture = nil then Exit;   // Get image dimensions 
SDL_QueryTexture(CurrentTexture, nil, nil, @ImgWidth, @ImgHeight);  
// Get panel dimensions  PanelWidth := Panel1.Width;  PanelHeight :=
Panel1.Height;   // Calculate aspect ratio to fit the image
proportionally  AspectRatio := Min(PanelWidth / ImgWidth, PanelHeight
/ ImgHeight);   DstRect.w := Round(ImgWidth * AspectRatio);  DstRect.h
:= Round(ImgHeight * AspectRatio);  DstRect.x := (PanelWidth -
DstRect.w) div 2;  DstRect.y := (PanelHeight - DstRect.h) div 2;  
StatusBar1.Panels[0].Text:= IntToStr(ImgWidth) +'x' +
inttostr(ImgHeight);   // Render the image 
SDL_RenderClear(SDLRenderer);  SDL_RenderCopy(SDLRenderer,
CurrentTexture, nil, @DstRect); 
SDL_RenderPresent(SDLRenderer);end; procedure
TForm1.HandleDropEvent(const FileName: string);begin 
LoadAndDisplayImage(FileName);end; procedure
TForm1.HandleSDLEvents;var  Event: TSDL_Event;begin  while
SDL_PollEvent(@Event) <> 0 do  begin    case Event.type_ of     
SDL_DROPFILE:        begin         
HandleDropEvent(string(Event.drop.file));         
SDL_free(Pointer(Event.drop.file)); // Clean up the file name string 
     end;      SDL_QUIT:        Close; // Handle quitting the
application    end;  end;end; procedure
TForm1.LoadAndDisplayImage(const FileName: string);begin   // Clean up
the old texture if it exists  if CurrentTexture <> nil then   
SDL_DestroyTexture(CurrentTexture);   // Load the new image as a
texture  CurrentTexture := IMG_LoadTexture(SDLRenderer,
PChar(FileName));  if CurrentTexture = nil then    raise
Exception.Create('Nie udało się wczytać tekstury: ' + IMG_GetError);  
// Render the image to fit the new size  RenderImage;end; procedure
TForm1.FormShow(Sender: TObject);begin   InitializeSDL;end; procedure
TForm1.Panel1Paint(Sender: TObject);begin  // Draw a red rectangle
(example)  SDL_SetRenderDrawColor(sdlRenderer, 0, 0, 0, 255); 
SDL_RenderFillRect(sdlRenderer, nil); // Full screen fill 
SDL_RenderPresent(sdlRenderer);    RenderImage;end; procedure
TForm1.FormDestroy(Sender: TObject);begin  ShutdownSDL;end; procedure
TForm1.Button1Click(Sender: TObject);begin  if OpenDialog1.Execute
then    begin      LoadAndDisplayImage(OpenDialog1.FileName);   
end;end; procedure TForm1.FormResize(Sender: TObject);begin 
RenderImage;end;  end.  
Regards

----------------------------------------------------------------------
korba812 · 2024-11-20 23:46

"file" is reserved word in pascal. To use a reserved word as an
identifier precede it with "&".
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
HandleDropEvent(string(Event.drop.&file));

----------------------------------------------------------------------
Pe3s · 2024-11-21 07:55

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.HandleSDLEvents;var  Event: TSDL_Event;begin  while
SDL_PollEvent(@Event) <> 0 do  begin    case Event.type_ of     
SDL_DROPFILE:        begin         
HandleDropEvent(string(Event.drop.&file));         
SDL_free(Pointer(Event.drop.&file)); // Clean up the file name string 
      end;      SDL_QUIT:        Close; // Handle quitting the
application    end;  end;end;         Code: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
unit1.pas(125,45) Error: identifier idents no member
"file"unit1.pas(126,39) Error: identifier idents no member
"file"unit1.pas(128,15) Error: Constant and CASE types do not
matchunit1.pas(128,15) Error: Constant Expression expected

----------------------------------------------------------------------
korba812 · 2024-11-21 09:59

Looking at the sources you provided, this field is named "_file":
https://github.com/ev1313/Pascal-SDL-2-
Headers/blob/201a767368020183b9964983d1c57ac4bd6a16fd/sdlevents.inc#L4
38

----------------------------------------------------------------------
Pe3s · 2024-11-21 12:24

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
 unit1.pas(132,17) Error: Constant and CASE types do not
matchunit1.pas(132,17) Error: Constant Expression expected  Code:
Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  Event:
TSDL_Event;begin  while SDL_PollEvent(@Event) <> 0 do  begin    case
Event.type_ of      SDL_DROPFILE:        begin         
HandleDropEvent(string(Event.drop._file));         
SDL_free(Pointer(Event.drop._file)); // Clean up the file name string 
      end;      SDL_QUIT:        Close; // Handle quitting the
application    end;  end;end;

----------------------------------------------------------------------
korba812 · 2024-11-21 12:47

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#L5
17C7-L517C17

----------------------------------------------------------------------
Pe3s · 2024-11-21 16:07

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

----------------------------------------------------------------------
Pe3s · 2024-11-21 21:43

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, ComCtrls, ExtCtrls,  StdCtrls, SDL2,
SDL2_image, Math; type   { TForm1 }   TForm1 = class(TForm)   
Button1: TButton;    OpenDialog1: TOpenDialog;    Panel1: TPanel;   
Panel2: TPanel;    StatusBar1: TStatusBar;    procedure
Button1Click(Sender: TObject);    procedure FormDestroy(Sender:
TObject);    procedure FormResize(Sender: TObject);    procedure
FormShow(Sender: TObject);    procedure Panel1Paint(Sender: TObject); 
private      SDLWindow: PSDL_Window;      SDLRenderer: PSDL_Renderer; 
    CurrentTexture: PSDL_Texture;      procedure InitializeSDL;     
procedure ShutdownSDL;      procedure LoadAndDisplayImage(const
FileName: string);      procedure RenderImage;      procedure
HandleDropEvent(const FilePath: string);      procedure
ProcessSDLEvents;   public   end; var  Form1: TForm1;   SDLEvent:
TSDL_Event; implementation {$R *.lfm} { TForm1 } procedure
TForm1.InitializeSDL;begin  if SDL_Init(SDL_INIT_VIDEO) < 0 then   
raise Exception.Create('Unable to initialize SDL: ' + SDL_GetError);  
// Ensure Panel1.Handle is correctly cast to a pointer  SDLWindow :=
SDL_CreateWindowFrom(Pointer(Panel1.Handle));  if SDLWindow = nil
then    raise Exception.Create('Unable to create SDL window: ' +
SDL_GetError);   // Create the renderer  SDLRenderer :=
SDL_CreateRenderer(SDLWindow, -1, SDL_RENDERER_ACCELERATED or
SDL_RENDERER_PRESENTVSYNC);  if SDLRenderer = nil then    raise
Exception.Create('Unable to create SDL renderer: ' + SDL_GetError);  
// Enable SDL's drop events  SDL_EventState(SDL_DROPFILE,
SDL_ENABLE);end; procedure TForm1.ShutdownSDL;begin   if
CurrentTexture <> nil then    SDL_DestroyTexture(CurrentTexture);  if
SDLRenderer <> nil then    SDL_DestroyRenderer(SDLRenderer);  if
SDLWindow <> nil then    SDL_DestroyWindow(SDLWindow);  IMG_Quit; 
SDL_Quit;end; procedure TForm1.RenderImage;var  DstRect: TSDL_Rect; 
ImgWidth, ImgHeight, PanelWidth, PanelHeight: Integer;  AspectRatio:
Double;begin  if CurrentTexture = nil then Exit;   // Get image
dimensions  SDL_QueryTexture(CurrentTexture, nil, nil, @ImgWidth,
@ImgHeight);   // Get panel dimensions  PanelWidth := Panel1.Width; 
PanelHeight := Panel1.Height;   // Calculate aspect ratio to fit the
image proportionally  AspectRatio := Min(PanelWidth / ImgWidth,
PanelHeight / ImgHeight);   DstRect.w := Round(ImgWidth *
AspectRatio);  DstRect.h := Round(ImgHeight * AspectRatio);  DstRect.x
:= (PanelWidth - DstRect.w) div 2;  DstRect.y := (PanelHeight -
DstRect.h) div 2;   StatusBar1.Panels[0].Text:= IntToStr(ImgWidth)
+'x' + inttostr(ImgHeight);   // Render the image 
SDL_RenderClear(SDLRenderer);  SDL_RenderCopy(SDLRenderer,
CurrentTexture, nil, @DstRect); 
SDL_RenderPresent(SDLRenderer);end; procedure
TForm1.HandleDropEvent(const FilePath: string);begin  // Load and
display the dropped image file  if FileExists(FilePath) then  begin  
LoadAndDisplayImage(FilePath);    Form1.Caption := 'Loaded: ' +
ExtractFileName(FilePath);  end  else    ShowMessage('Invalid file
dropped: ' + FilePath);end; procedure TForm1.ProcessSDLEvents;begin 
while SDL_PollEvent(@SDLEvent) <> 0 do  begin    case SDLEvent.type_
of      SDL_DROPFILE:        begin         
HandleDropEvent(SDLEvent.drop._file);         
SDL_free(SDLEvent.drop._file); // Free the file path allocated by SDL 
      end;      SDL_QUITEV:        begin          Close;        end; 
 end;  end;end; procedure TForm1.LoadAndDisplayImage(const FileName:
string);begin   // Clean up the old texture if it exists  if
CurrentTexture <> nil then    SDL_DestroyTexture(CurrentTexture);   //
Load the new image as a texture  CurrentTexture :=
IMG_LoadTexture(SDLRenderer, PChar(FileName));  if CurrentTexture =
nil then    raise Exception.Create('Nie udało się wczytać tekstury: '
+ IMG_GetError);   // Render the image to fit the new size 
RenderImage;end; procedure TForm1.FormShow(Sender: TObject);begin 
 InitializeSDL; end; procedure TForm1.Panel1Paint(Sender:
TObject);begin  // Draw a red rectangle (example) 
SDL_SetRenderDrawColor(sdlRenderer, 0, 0, 0, 255); 
SDL_RenderFillRect(sdlRenderer, nil); // Full screen fill 
SDL_RenderPresent(sdlRenderer);    RenderImage;end; procedure
TForm1.FormDestroy(Sender: TObject);begin  ShutdownSDL;end; procedure
TForm1.Button1Click(Sender: TObject);begin  if OpenDialog1.Execute
then    begin      LoadAndDisplayImage(OpenDialog1.FileName);   
end;end; procedure TForm1.FormResize(Sender: TObject);begin  
RenderImage;end;  end.

----------------------------------------------------------------------
TRon · 2024-11-22 00:35

Quote from: Pe3s on November 21, 2024, 10:43:23 pmWhat 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 · 2024-11-22 07:23

The drag and drop function from Lazarus does not work from the SDL
window.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormDropFiles(Sender: TObject; const FileNames: array of
string);var  i: Integer;begin  for i := Low(FileNames) to
High(FileNames) do     LoadAndDisplayImage(FileNames[i]);end;

----------------------------------------------------------------------
Pe3s · 2024-11-22 08:33

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

----------------------------------------------------------------------
TRon · 2024-11-22 08:57

Quote from: Pe3s on November 22, 2024, 08:23:57 amThe 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).

Quote from: Pe3s on November 22, 2024, 09:33:37 amHow 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 · 2024-11-22 09:11

This sdl code should handle file dropping.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.HandleSDLEvents;var  Event: TSDL_Event;begin  while
SDL_PollEvent(@Event) <> 0 do  begin    case Event.type_ of     
SDL_DROPFILE:        begin         
HandleDropEvent(string(Event.drop.file));         
SDL_free(Pointer(Event.drop.file)); // Clean up the file name string 
     end;      SDL_QUIT:        Close; // Handle quitting the
application    end;  end;end;

----------------------------------------------------------------------
Seenkao · 2024-11-22 11:01

Quote from: Pe3s on November 22, 2024, 09:33:37 amHow 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 · 2024-11-22 11:08

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

----------------------------------------------------------------------
Pe3s · 2024-11-23 08:47

Why is there a function “ SDL_DROPFILE” as it does not work.
And if it works there is no example of correct usage.

----------------------------------------------------------------------
jamie · 2024-11-23 15:38

Shooting from the hip, because I am stupid, have you tried enabling
the "AllowDropFiles" in the form?

Jamie

----------------------------------------------------------------------
TRon · 2024-11-23 15:47

@Jamie:
That wouldn't help in any way.

The SDL eventloop is never ran.

@Pe3s:
Normally SDL creates its own window and takes responsibility for
'catching' the events that are generated from the 'outside'. Because
the SDL window is embedded in a LCL control SDL is not able to take
care of that unless running in a SDL eventloop (again: a loop that is
never ran).


So, use the form drag and drop events.

Anything else is just pure speculation because there is no description
of what the end-goal actually is.

As I wrote before, the concept of your solution simply does not
compute.

And no matter what, either using form events or SDL events the code
still needs to handle those events and actually do something with the
filename. It does not matter where that exactly is done (in SDL or
LCL).

In basics the SDL in the panel right now is nothing more than a
glorified image control and should be treated the same.

----------------------------------------------------------------------
Pe3s · 2024-11-23 15:56

I want to open the dropped file as it is done via open dialog.
the sdl window does not support dropping files. OnDropFiles of
Lazarus. If we drop them on the form, they load, but most of the
window is occupied by the sdl window.
The matter would be simple if the sdl window inherited the lcl event
handler

----------------------------------------------------------------------
jamie · 2024-11-23 15:59

Ok, I know in windows you need to register the window handle for it to
receive drop file notifications.

In other targets, I have no idea.

----------------------------------------------------------------------
TRon · 2024-11-23 16:01

Quote from: Pe3s on November 23, 2024, 04:56:55 pmThe matter would be
simple if the sdl window inherited the lcl event handler
Yes, that would solve it but SDL doesn't (how could it ?).

As a test you could try an use the onidle event of the application to
run your SDL event poll and see if SDL at least generates the event.

In case that doesn't work then the only way that I know of is to use
the form events and handling things manually.

----------------------------------------------------------------------
jamie · 2024-11-23 16:16

Last time I remember, those Messages from the OS in windows are
blocked and only the embedded support for the drag and drop that the
LCL works because it's handled elsewhere to allow it. But basically,
they are blocked thus you need to actually hook into the message event
to see it.

 I've ported over code from Delphi doing Drag and Drop and wouldn't
work in the LCL because of these messages being blocked and had to
resort to hooking it.

 I do have a unit to make it easy to insert blocked messages for the
form but its only for the LCL/Laz because Delphi does not have this
issue.

 Have a good day.

Jamie

----------------------------------------------------------------------
TRon · 2024-11-23 16:20

Indeed, something like that should be able to do the trick jamie.

However these kind of things are usually not for the casual user.

There is a reason I hinted at having a look at the gl controls because
they need to do something similar and based on that one could probably
come up with an embedded SDL control (in case it doesn't exist yet).

----------------------------------------------------------------------
jamie · 2024-11-23 17:14

On the windows side of things, it's possible the whole thing is
blocked and even the LCL support may not work if you have one these
conditions.

https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-
winuser-changewindowmessagefilterex
 This also has something to do with app elevations permissions.
Jamie

----------------------------------------------------------------------
Pe3s · 2024-11-24 08:19

Thank you for your help in solving the problem.
Application.OnIdle solved the problem

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.ApplicationIdle(Sender: TObject; var Done: Boolean);begin 
ProcessSDLEvents;  Done := False;end; 
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormShow(Sender: TObject);begin  InitializeSDL; 
Application.OnIdle := @ApplicationIdle;end; 
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormDestroy(Sender: TObject);begin  Application.OnIdle := nil; 
ShutdownSDL;end;