Upto: Table of Contents of full book "Programming Wayland Clients"

This project hasn't been updated since mid-2017. Wayland has moved on since then, so the information here may be out of date, and there is no guarantee the programs still work. You are recommended to look at The Wayland Protocol for more up-todate information, or at A better way to read Wayland documentation . .

SDL

SDL (Simple DirectMedia Layer) is a cross-platform multimedia framework. It has suport fro Wayland since version 2.0.2.

Resources

Installing

Writing SDL applications requires the RPM package SDL2-devel under Fedora and libsdl2-dev under Ubuntu.

A simple SDL application

To demonstrate SDL and Wayland we don't need a complex application, just a simple window will do. The following application draws a window and exits after 10 seconds window.c:

/* From http://lazyfoo.net/tutorials/SDL/01_hello_SDL/index2.php */

#include <SDL.h>
#include <stdio.h>

//Screen dimension constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

int main( int argc, char* args[] )
{
    //The window we'll be rendering to
    SDL_Window* window = NULL;
    
    //The surface contained by the window
    SDL_Surface* screenSurface = NULL;

    //Initialize SDL
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    {
        printf( "SDL could not initialize! SDL_Error: %s\n", SDL_GetError() );
    }
    else
    {
        //Create window
        window = SDL_CreateWindow( "SDL Tutorial", SDL_WINDOWPOS_UNDEFINED,
				   SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH,
				   SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
        if( window == NULL )
        {
            printf( "Window could not be created! SDL_Error: %s\n", SDL_GetError() );
        }
       else
        {
            //Get window surface
            screenSurface = SDL_GetWindowSurface( window );

            //Fill the surface white
            SDL_FillRect( screenSurface, NULL, SDL_MapRGB( screenSurface->format, 0xFF, 0xFF, 0xFF ) );
            
            //Update the surface
            SDL_UpdateWindowSurface( window );

            //Wait ten seconds
            SDL_Delay( 10000 );
        }
    }
    //Destroy window
    SDL_DestroyWindow( window );

    //Quit SDL subsystems
    SDL_Quit();

    return 0;
}

It can be built using the Makefile

CFLAGS = $(shell pkg-config --cflags sdl2)
LDLIBS= $(shell pkg-config --libs sdl2)

EXE = window wayland_info

all: $(EXE)

Running under X or Wayland

The default is to run under X:

        
          ./window

runs as an X application with an X window. To run under Wayland, set the environment variable SDL_VIDEODRIVER:

        
          SDL_VIDEODRIVER=wayland ./window

This runs as a Wayland application, native on Fedora, in Weston on Ubuntu.

Getting a wayland surface

If you need to get a Wayland surface this is done by getting the system structure SDL_GetWindowWMInfo. This contains a union of information for different backends. For Wayland, the relevant calls are given in the program wayland_info.c

#include "SDL.h"
#include "SDL_syswm.h"
#include <wayland-client.h>

int main(int argc, char *argv[]) {
  SDL_Window* window;
  SDL_SysWMinfo info;

  SDL_Init(0);

  window = SDL_CreateWindow("", 0, 0, 0, 0, SDL_WINDOW_HIDDEN);

   if (SDL_GetWindowWMInfo(window,&info)) {
    /* success */
    if (info.subsystem == SDL_SYSWM_WAYLAND) {
      printf("Is Wayland\n");
      
      struct wl_display* display = info.info.wl.display;
      struct wl_surface* surface = info.info.wl.surface;
      struct wl_shell_surface* shell_surface = info.info.wl.shell_surface;
      // and do whatever you want with the Wayland stuff
    } else {
      printf("Not a Wayland system\n");
    }
   } else {
     printf("Failed to get WM info\n");
   }
}

Conclusion

Building SDL applications for Wayland is straightforward: without any changes to the source code, run the executable with the environment variable SDL_VIDEODRIVER set to wayland. Access to the Wayland display and applications's Wayland surface is straightforward.

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