Games at Bolton Simple Directmedia Layer Andrew Williams

Games at Bolton 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

Games at Bolton 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: – –Our use of the library falls within the LGPL

Games at Bolton SDL Resources  SDL Homepage: – You can download SDL from the SDL homepage – A documentation project for SDL – A (rather good) series of tutorials

Games at Bolton 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

Games at Bolton 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

Games at Bolton 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

Games at Bolton 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

Games at Bolton 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);

Games at Bolton 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; }

Games at Bolton 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; }

Games at Bolton 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); }

Games at Bolton 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?

Games at Bolton 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?

Games at Bolton 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?