Game programming/Basic SDL

Simple Directmedia Layer, SDL, is a wrapper library which abstracts away OS-specific code from the programmer.

Purpose

• Learn the structure, and how to make a simple SDL application

Requirements

• C knowledge
• Dependencies installed

Dependencies

• Go get SDL from here
• Install it in your environment, add include and lib directories
• Link with libSDLmain.a (SDLmain.lib) and libSDL.a (SDL.lib)

Basic SDL program structure

#include "SDL.h"

#define CAPTION           "Application name"
#define RESOLUTION_WIDTH  640
#define RESOLUTION_HEIGHT 480
#define COLOR_DEPTH       0 /* Can be any value. 0 stands for whatever color depth is currently selected */
#define FLAGS             0

static int running = 0;

static void handleEvent(const SDL_Event sdl_event);
static void render(SDL_Surface* screen);

int main(int argc, char* argv[])
{
    SDL_Surface *window  = NULL;
    
    if(SDL_Init(SDL_INIT_EVERYTHING) == -1) /* if SDL_Init fails */
    {
        return 1;
    }
    SDL_WM_SetCaption(CAPTION, NULL);
    window = SDL_SetVideoMode(RESOLUTION_WIDTH, RESOLUTION_HEIGHT, COLOR_DEPTH, FLAGS);
    if(window == NULL) /* SDL_SetVideoMode failed */
    {
        SDL_Quit();
        return 1;
    }
    
    running = 1;
    while(running)
    {
        SDL_Event sdl_event;
        
        while(SDL_PollEvent(&sdl_event) > 0) /* Run as long as there are available events and fill sdl_event with their information */
        {
            handleEvent(sdl_event);
        }
        
        SDL_FillRect(screen, NULL, 0); /* Clears the screen */
        render(screen);
        SDL_Flip(screen); /* Draws the screen */
    }
    
    SDL_Quit();
    return 0;
}

static void handleEvent(const SDL_Event sdl_event)
{
    switch(sdl_event.type)
    {
    /* Event handling goes here */
    case(SDL_QUIT):
        running = 0;
        break;
    }
}

static void render(SDL_Surface* screen)
{
    /* Rendering code goes here */
}

Rendering

The following code renders a blue rectangle, 128 pixels wide and 16 pixels high, 32 pixels from the left edge of the window, and 64 pixels from it's top.

static void render(SDL_Surface* screen)
{
    SDL_Rect rectangle;
    
    rectangle.x = 32;  /* Location on X plane */
    rectangle.y = 64;  /* Location on Y plane */
    rectangle.w = 128; /* Width  */
    rectangle.h = 16;  /* Height */
    
    SDL_FillRect(screen, &(rectangle), SDL_MapRGB(screen->format, 0, 0, 255)); /* Screen format, Red, Green, Blue */
}

Trivia

• SDL's co-ordinates system uses pixels, with the bird at the upper-left corner of the window. The positive X direction is right, and positive Y direction is down.
• SDL is a wrapper. This means that it uses the OSes own API for the work it does. When you're using SDL on windows, you're actually using Win32. On GNU+Linux, you use whatever desktop environment is currently running.