Versione attuale delle 16:35, 18 mar 2024

La risorsa SDL2 mette a disposizione alcune librerie contenenti varie funzioni che consentono, fra l'altro, anche la creazione di finestre ove visualizzare testo, immagini ed altro.

Per creare e gestire in modo adeguato le finestre, bisognerà servirsi della seguente libreria condivisa: libSDL2-2.0.so.0.3000.0

Creare una finestra colorata e disegnarvi un quadrato

Mostriamo di seguito un semplice esempio per generare una finestra colorata di giallo, nella quale sarà disegnato un quadrato pieno di colore blu:

Library "libSDL2-2.0:0.3000.0"

Public Struct SDL_Rect 
  x As Integer
  y As Integer
  w As Integer
  h As Integer
End Struct

Private Const SDL_INIT_VIDEO As Integer = &20
Private Const SDL_WINDOW_SHOWN As Integer = 4
Private Enum SDL_RENDERER_SOFTWARE = 1, SDL_RENDERER_ACCELERATED, SDL_RENDERER_PRESENTVSYNC = 4, SDL_RENDERER_TARGETTEXTURE = 8

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' SDL_Window* SDL_CreateWindow(const char* title, int x, int y, int w, int h, Uint32 flags)
' Creates a window with the specified position, dimensions, and flags.
Private Extern SDL_CreateWindow(title As String, xI As Integer, yI As Integer, width As Integer, height As Integer, flags As Integer) As Pointer

' const char* SDL_GetError(void)
' Returns a message with information about the specific error that occurred.
Private Extern SDL_GetError() As String

' SDL_Renderer* SDL_CreateRenderer(SDL_Window* window, int index, Uint32 flags)
' Creates a 2D rendering context for a window.
Private Extern SDL_CreateRenderer(sdl_window As Pointer, index As Integer, flags As Integer) As Pointer

' int SDL_SetRenderDrawColor(SDL_Renderer * renderer,  Uint8 r, Uint8 g, Uint8 b, Uint8 a)
' Sets the color used for drawing operations (Rect, Line and Clear).
Private Extern SDL_SetRenderDrawColor(renderer As Pointer, rB As Byte, gB As Byte, bB As Byte, aB As Byte) As Integer

' int SDL_RenderClear(SDL_Renderer* renderer)
' Clears the current rendering target with the drawing color.
Private Extern SDL_RenderClear(renderer As Pointer) As Integer

' int SDL_RenderDrawRect(SDL_Renderer * renderer, const SDL_Rect* rect)
' Draws a rectangle on the current rendering target.
Private Extern SDL_RenderDrawRect(renderer As Pointer, rect As SDL_Rect) As Integer

' int SDL_RenderFillRect(SDL_Renderer * renderer, const SDL_Rect* rect)
' Fills a rectangle on the current rendering target with the drawing color.
Private Extern SDL_RenderFillRect(renderer As Pointer, rect As SDL_Rect) As Integer

' void SDL_RenderPresent(SDL_Renderer * renderer)
' Update the screen with rendering performed.
Private Extern SDL_RenderPresent(renderer As Pointer)

' void SDL_DestroyWindow(SDL_Window* window)
' Destroy a window.
Private Extern SDL_DestroyWindow(sdl_window As Pointer)

' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Public Sub Main()

 Dim finestra, rend As Pointer
 Dim riquadro As New SDL_Rect
 Dim s As String

 SDL_Init(SDL_INIT_VIDEO)
 
 finestra = SDL_CreateWindow("Titolo finestra", 50, 50, 640, 480, SDL_WINDOW_SHOWN)
 If finestra == 0 Then Error.Raise("Impossibile creare la finestra: " & SDL_GetError())

 rend = SDL_CreateRenderer(finestra, 0, SDL_RENDERER_ACCELERATED)
 If rend == 0 Then Error.Raise("Errore alla funzione 'SDL_CreateRenderer': " & SDL_GetError())

 SDL_SetRenderDrawColor(rend, 255, 255, 0, 255)

 SDL_RenderClear(rend)

' Si imposta un riquadro 50x50 pixel all'interno della finestra:
 With riquadro
   .x = 20
   .y = 20
   .w = 50
   .h = 50
 End With

' Viene impostato il colore blu per i margini del riquadro:
 SDL_SetRenderDrawColor(rend, 0, 0, 255, 255)
' Viene disegnato il riquadro:
 SDL_RenderDrawRect(rend, riquadro)
' Il riquadro viene colorato di blu anche al suo interno:
 SDL_RenderFillRect(rend, riquadro)

 SDL_RenderPresent(rend)

 ' Per tenere aperta la finestra utilizziamo il seguente ciclo, dal quale si uscirà solo quando si invierà un qualsiasi carattere dalla console o dal Terminale:
 Repeat
   Input #File.In, s
 Until s <> Null

' Va in chiusura:
  SDL_DestroyWindow(finestra)
  SDL_Quit()

End

Creare una finestra e caricarvi un'immagine

Mostriamo di seguito un semplice esempio per generare una finestra e caricarvi un'immagine. In questo caso la dimensione della finestra avrà le medesime dimensioni dell'immagine.
Poiché si farà uso della funzione ImageStat(), sarà necessario attivare il componente gb.image .

Library "libSDL2-2.0:0.3000.0"

Private Const SDL_INIT_VIDEO As Integer = &20
Private Const SDL_WINDOW_SHOWN As Integer = 4
Private Const SDL_WINDOWEVENT_CLOSE As Integer = 14
Private Const SDL_WINDOWEVENT As Integer = &200
Private Const SDL_KEYDOWN As Integer = &300
Private Const SDL_SCANCODE_ESCAPE As Integer = 41
Private Enum SDL_RENDERER_SOFTWARE = 1, SDL_RENDERER_ACCELERATED, SDL_RENDERER_PRESENTVSYNC = 4, SDL_RENDERER_TARGETTEXTURE = 8

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' SDL_Window* SDL_CreateWindow(const char* title, int x, int y, int w, int h, Uint32 flags)
' Creates a window with the specified position, dimensions, and flags.
Private Extern SDL_CreateWindow(title As String, xI As Integer, yI As Integer, width As Integer, height As Integer, flags As Integer) As Pointer

' const char* SDL_GetError(void)
' Returns a message with information about the specific error that occurred.
Private Extern SDL_GetError() As String

' SDL_Renderer* SDL_CreateRenderer(SDL_Window* window, int index, Uint32 flags)
' Creates a 2D rendering context for a window.
Private Extern SDL_CreateRenderer(sdl_window As Pointer, index As Integer, flags As Integer) As Pointer

' int SDL_RenderClear(SDL_Renderer* renderer)
' Clears the current rendering target with the drawing color.
Private Extern SDL_RenderClear(renderer As Pointer) As Integer

' int SDL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture, const SDL_Rect * srcrect, const SDL_Rect * dstrect)
' Copy a portion of the texture to the current rendering target.
Private Extern SDL_RenderCopy(renderer As Pointer, texture As Pointer, srcrect As Pointer, dstrect As Pointer) As Integer

' void SDL_RenderPresent(SDL_Renderer * renderer)
' Update the screen with rendering performed.
Private Extern SDL_RenderPresent(renderer As Pointer)

' int SDL_WaitEvent(SDL_Event* event)
' Wait indefinitely for the next available event.
Private Extern SDL_WaitEvent(SDL_event As Pointer) As Integer

' void SDL_DestroyWindow(SDL_Window* window)
' Destroy a window.
Private Extern SDL_DestroyWindow(sdl_window As Pointer)
 
' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Library "libSDL2_image-2.0:0.2.3"

' SDL_Texture * IMG_LoadTexture(SDL_Renderer *renderer, const char *file)
' Load an image directly into a render texture.
Private Extern IMG_LoadTexture(renderer As Pointer, _file As String) As Pointer


Public Sub Main()
 
 Dim finestra, rend, tex, ev As Pointer
 Dim file_immagine As String
 Dim wImm, hImm As Integer
  
 file_immagine = "/percorso/del/file/immagine"
 wImm = ImageStat(file_immagine).Width
 hImm = ImageStat(file_immagine).Height
  
 SDL_Init(SDL_INIT_VIDEO)
 
 finestra = SDL_CreateWindow("Titolo finestra", 50, 50, wImm, hImm, SDL_WINDOW_SHOWN)
 If finestra == 0 Then Error.Raise("Impossibile creare la finestra: " & SDL_GetError())
 
 rend = SDL_CreateRenderer(finestra, -1, SDL_RENDERER_ACCELERATED Or SDL_RENDERER_PRESENTVSYNC)
 If rend == 0 Then Error.Raise("Errore alla funzione 'SDL_CreateRenderer': " & SDL_GetError())
  
' Carica un'immagine nella finestra:
 tex = IMG_LoadTexture(rend, file_immagine)
  
 SDL_RenderClear(rend)
 SDL_RenderCopy(rend, tex, 0, 0)
 SDL_RenderPresent(rend)

 ev = Alloc(SizeOf(gb.Byte), 56)
  
' Resta in attesa che l'utente prema il tasto "Esc" per chiudere la finestra ed il programma:
 Do
   SDL_WaitEvent(ev)
' Individua il membro 'key' della "Union" 'SDL_Event':
   Select Case Int@(ev)
     Case SDL_KEYDOWN
' Se il valore del puntatore dereferenziato corrisponde al tasto "Esc", esce dal ciclo.
       If Int@(ev + 16) = SDL_SCANCODE_ESCAPE Then Break
     Case SDL_WINDOWEVENT
' Se il valore del puntatore dereferenziato corrisponde alla richiesta con il mouse di chiusura della finestra, esce dal ciclo.
       If Int@(ev + 12) = SDL_WINDOWEVENT_CLOSE Then Break
   End Select    
 Loop

' Libera la memoria precedentemente occupata e va in chiusura:
  Free(ev)
  ev = 0
  SDL_DestroyWindow(finestra)
  SDL_Quit()

End

Creare una finestra colorata e modificare l'aspetto del puntatore del mouse

In quest'altro esempio viene generata una finestra colorata di giallo e viene modificato l'aspetto del puntatore del mouse, che apparirà nel suo nuovo aspetto quando entrerà nella finestra.

Private cursore As String[] = ["    32    32        3            1",
 "X c #000000",
 ". c #FFFFFF",
 "  c None",
 "X                               ",
 "XX                              ",
 "X.X                             ",
 "XXXX                            ",
 "X...X                           ",
 "XXXXXX                          ",
 "X.....X                         ",
 "XXXXXXXX                        ",
 "X.......X                       ",
 "XXXXXXXXXX                      ",
 "X.....XXXXX                     ",
 "XXXXXXX                         ",
 "X.X X..X                        ",
 "XX  XXXX                        ",
 "X    X..X                       ",
 "     XXXX                       ",
 "      X..X                      ",
 "      XXXX                      ",
 "       XX                       ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "                                ",
 "0,0"]
 
Private s As String

Library "libSDL2-2.0:0.3000.0"

Private Const SDL_INIT_VIDEO As Integer = &20
Private Const SDL_WINDOWPOS_CENTERED As Integer = &2FFF0000
Private Const SDL_WINDOW_SHOWN As Integer = 4
Private Const SDL_WINDOWEVENT_CLOSE As Integer = 14
Private Const SDL_WINDOWEVENT As Integer = &200
Private Const SDL_KEYDOWN As Integer = &300
Private Const SDL_SCANCODE_ESCAPE As Integer = 41
Private Enum SDL_RENDERER_SOFTWARE = 1, SDL_RENDERER_ACCELERATED, SDL_RENDERER_PRESENTVSYNC = 4, SDL_RENDERER_TARGETTEXTURE = 8

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' SDL_Window* SDL_CreateWindow(const char* title, int x, int y, int w, int h, Uint32 flags)
' Creates a window with the specified position, dimensions, and flags.
Private Extern SDL_CreateWindow(title As String, xI As Integer, yI As Integer, width As Integer, height As Integer, flags As Integer) As Pointer

' const char* SDL_GetError(void)
' Returns a message with information about the specific error that occurred.
Private Extern SDL_GetError() As String

' SDL_Renderer* SDL_CreateRenderer(SDL_Window* window, int index, Uint32 flags)
' Creates a 2D rendering context for a window.
Private Extern SDL_CreateRenderer(sdl_window As Pointer, index As Integer, flags As Integer) As Pointer

' int SDL_SetRenderDrawColor(SDL_Renderer * renderer,  Uint8 r, Uint8 g, Uint8 b, Uint8 a)
' Sets the color used for drawing operations (Rect, Line and Clear).
Private Extern SDL_SetRenderDrawColor(renderer As Pointer, rB As Byte, gB As Byte, bB As Byte, aB As Byte) As Integer

' int SDL_RenderClear(SDL_Renderer* renderer)
' Clears the current rendering target with the drawing color.
Private Extern SDL_RenderClear(renderer As Pointer) As Integer
  
' void SDL_RenderPresent(SDL_Renderer * renderer)
' Update the screen with rendering performed.
Private Extern SDL_RenderPresent(renderer As Pointer)

' SDL_Cursor* SDL_CreateCursor(const Uint8* data, const Uint8* mask, int w, int h, int hot_x, int hot_y)
' To create a cursor using the specified bitmap data and mask (in MSB format).
Private Extern SDL_CreateCursor(data As Pointer, mask As Pointer, w As Integer, h As Integer, hot_x As Integer, hot_y As Integer) As Pointer

' void SDL_SetCursor(SDL_Cursor* cursor)
' To set the active cursor.
Private Extern SDL_SetCursor(cursor As Pointer)

' int SDL_WaitEvent(SDL_Event* event)
' Wait indefinitely for the next available event.
Private Extern SDL_WaitEvent(SDL_event As Pointer) As Integer

' void SDL_DestroyWindow(SDL_Window* window)
' Destroy a window.
Private Extern SDL_DestroyWindow(sdl_window As Pointer)

' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Public Sub Main()

 Dim finestra, rend, cur, ev As Pointer
  
 SDL_Init(SDL_INIT_VIDEO)
 
 finestra = SDL_CreateWindow("Titolo finestra", 50, 50, 640, 480, SDL_WINDOW_SHOWN)
 If finestra == 0 Then Error.Raise("Impossibile creare la finestra: " & SDL_GetError())

 rend = SDL_CreateRenderer(finestra, 0, SDL_RENDERER_ACCELERATED)
 If rend == 0 Then Error.Raise("Impossibile creare un contesto rendering 2D per la finestra: " & SDL_GetError())

 SDL_SetRenderDrawColor(rend, 255, 255, 0, 255)

 SDL_RenderClear(rend)

 SDL_RenderPresent(rend)
  
 cur = CreaCursore()
  
 SDL_SetCursor(cur)

 ev = Alloc(SizeOf(gb.Byte), 56)
  
' Resta in attesa che l'utente prema il tasto "Esc" per chiudere la finestra ed il programma:
 Do
   SDL_WaitEvent(ev) 
' Individua il membro 'key' della "Union" 'SDL_Event':
   Select Case Int@(ev)
     Case SDL_KEYDOWN
' Se il valore del puntatore dereferenziato corrisponde al tasto "Esc", esce dal ciclo.
       If Int@(ev + 16) = SDL_SCANCODE_ESCAPE Then Break
     Case SDL_WINDOWEVENT
' Se il valore del puntatore dereferenziato corrisponde alla richiesta con il mouse di chiusura della finestra, esce dal ciclo.
       If Int@(ev + 12) = SDL_WINDOWEVENT_CLOSE Then Break
   End Select         
 Loop

' Libera la memoria precedentemente occupata e va in chiusura:
  Free(ev)
  SDL_DestroyWindow(finestra)
  SDL_Quit()

End


Private Function CreaCursore() As Pointer

 Dim i, row, col As Integer
 Dim data As New Byte[4 * 32]
 Dim mask As New Byte[4 * 32]
 
 i = -1
  
 For row = 0 To 32 - 1
   For col = 0 To 32 - 1
     If col Mod 8 Then
       data[i] = Shl(data[i], 1)
       mask[i] = Shl(mask[i], 1)
     Else
       Inc i
       mask[i] = 0
       data[i] = mask[i] 
     Endif
     Select Case Mid(cursore[4 + row], col + 1, 1)
       Case "X"
         data[i] = data[i] Or &01
         mask[i] = mask[i] Or &01
       Case "."
         mask[i] = mask[i] Or &01
     End Select
   Next
 Next
   
 Return SDL_CreateCursor(data.data, mask.data, 32, 32, Left(cursore[4 + row], 1), Right(cursore[4 + row], 1))
 
End

Riferimenti

• http://www.libsdl.org
• https://wiki.libsdl.org/FrontPage
• http://www.willusher.io/pages/sdl2/
• http://headerphile.com