1. Copyright © 2002 Bolton Institute Simple Directmedia Layer (SDL) Andrew Williams A.Williams@bolton.ac.uk A.Williams@bolton.ac.uk 01204-903839

2. Copyright © 2002 Bolton Institute What is SDL? SDL is a library (a standardized set of functions) for doing: –Games –Multimedia type applications It is rather lightweight –Nothing like as much functionality as BlitzBasic, for example You might create something like BlitzBasic with SDL

3. Copyright © 2002 Bolton Institute SDL History Created by Sam Lantinga Used by Loki Games in their short-lived attempt to port various games to Linux Licensed under the LGPL: –http://www.libsdl.org/license.phphttp://www.libsdl.org/license.php –Our use of the library falls within the LGPL

4. Copyright © 2002 Bolton Institute SDL Resources SDL Homepage: –http://www.libsdl.org/http://www.libsdl.org/ You can download SDL from the SDL homepage –http://sdldoc.csn.ul.ie/http://sdldoc.csn.ul.ie/ A documentation project for SDL –http://cone3d.gamedev.net/cgi- bin/index.pl?page=tutorials/gfxsdl/index A (rather good) series of tutorials

5. Copyright © 2002 Bolton Institute SDL vs DirectX SDL –Simple –Started on Linux Now cross-platform –Patchy documentation –Development is ad hoc Some talented people working part-time –Something of a hobby DirectX –Very sophisticated –Standard on Windows Windows only –Superb documentation –Development is very well organized Very bright people –Strategic product for Microsoft

6. Copyright © 2002 Bolton Institute SDL vs DirectX Not really a like-for-like comparison –On Windows, SDL sits on top of DirectX to get the very best acceleration out of modern graphics hardware DirectX is highly integrated –Direct3D –DirectSound SDL uses –OpenGL –SDL_mixer

7. Copyright © 2002 Bolton Institute SDL components SDL –The basic library SDL_mixer –Dynamic audio mixing and streaming SDL_image –Loading image files (apart from BMP) We'll use other stuff as we find it

8. Copyright © 2002 Bolton Institute SDL Basics Initializing the SDL system SDL_Init(Uint32 flags); Uint32 means 32-bit unsigned integer flags is the parameter to the function We have to create a number to tell SDL which parts we want to initialize. We have several possibilities: –SDL_INIT_TIMER –SDL_INIT_VIDEO –SDL_INIT_AUDIO –SDL_INIT_JOYSTICK –etc

9. Copyright © 2002 Bolton Institute SDL Basics In the first tutorial, we initialize the video and the audio We combine the numbers with a bit-wise OR operation (don't worry if you don't understand that): SDL_Init(INIT_VIDEO | INIT_AUDIO);

10. Copyright © 2002 Bolton Institute SDL Basics In practice, it's not a good idea to assume that the function succeeded. We should really test it: if( SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO) < 0 ) { printf("Unable to init SDL: %s\n", SDL_GetError()); return 1; }

11. Copyright © 2002 Bolton Institute SDL Basics Creating a surface to draw on 1.Declare a variable 2.Call the function 3.Check for error SDL_Surface *screen; screen = SDL_SetVideoMode(640, 480, 32, SDL_HWSURFACE|SDL_DOUBLEBUF); if ( screen == NULL ) { printf("Unable to set 640x480 video: %s\n", SDL_GetError()); return 1; }

12. Copyright © 2002 Bolton Institute Drawing the Scene void DrawScene(SDL_Surface *screen) { Slock(screen); for(int x=0;x<640;x++) { for(int y=0;y<480;y++) { DrawPixel(screen,x,y,y/2,y/3,x/3); } Sulock(screen); SDL_Flip(screen); }

13. Copyright © 2002 Bolton Institute Drawing the Scene void DrawScene(SDL_Surface *screen) { Slock(screen); for(int x=0;x<640;x++) { for(int y=0;y<480;y++) { DrawPixel(screen,x,y,y/2,y/3,x/3); } Sulock(screen); SDL_Flip(screen); } Question: What do the parameters to DrawPixel represent?

14. Copyright © 2002 Bolton Institute Drawing the Scene void DrawScene(SDL_Surface *screen) { Slock(screen); for(int x=0;x<640;x++) { for(int y=0;y<480;y++) { DrawPixel(screen,x,y,y/2,y/3,x/3); } Sulock(screen); SDL_Flip(screen); } Question: What do Slock and Sulock do?

15. Copyright © 2002 Bolton Institute Exercises Questions –What does atexit(SDL_QUIT); do? –What is the error condition for SDL_Init(...) ? Tasks –Alter DrawScene(...) so that the calls to DrawPixel(..) use constant values (eg 50 or 100 ) instead of y/2, y/2 and x/3 What happens?