Outils pour utilisateurs
**Ceci est une ancienne révision du document !** ----
===== Displays ===== In this section we will walk through a simple example, explaining how to create a display and setting optional properties for the display. ==== Basic Example ==== Here we demonstrate how to create a display, clear the display, display it for 10 seconds, and exit. === Code === <file c main> #include <stdio.h> #include <allegro5/allegro.h> int main(int argc, char **argv) { ALLEGRO_DISPLAY *display = NULL; if(!al_init()) { fprintf(stderr, "failed to initialize allegro!\n"); return -1; } display = al_create_display(640, 480); if(!display) { fprintf(stderr, "failed to create display!\n"); return -1; } al_clear_to_color(al_map_rgb(0,0,0)); al_flip_display(); al_rest(10.0); al_destroy_display(display); return 0; } </file> === Walk through === These walk throughs will explain important lines of code in the examples. <code c>#include <stdio.h> #include <allegro5/allegro.h></code> Here we include the headers necessary for this example. **stdio.h** is required for the **fprintf** function, and **allegro5/allegro.h** is necessary for all of the allegro functions that are used in this example. <code c>int main(int argc, char **argv) {</code> A standard main function, with the argument count and argument vector parameters. <code c>if(!al_init()) { fprintf(stderr, "failed to initialize allegro!\n"); return -1; }</code> Here we initialize the Allegro library. If it should fail, it will return false, and the <code>if()</code> block will execute, printing a message to standard error, and then exit. <code c>display = al_create_display(640, 480);</code> **al_create_display** will create a display with the given width and height. Should **al_create_display** fail to create a display for some reason, it will return **NULL**. <code c> if(!display) { fprintf(stderr, "failed to create display!\n"); return -1; } </code> Should **al_create_display** fail, we trigger this if block, print a failure message, and then exit. <code c>al_clear_to_color(al_map_rgb(0,0,0));</code> **al_map_rgb** takes three arguments, the value for the red, green, and blue components of the color respectively, and will return a **ALLEGRO_COLOR** structure. **al_clear_to_color** clears the current display //the one we just created// to a given color. <code c>al_flip_display();</code> Allegro, by default, creates two image buffers -- the one being displayed on the screen, and the one being drawn on in the code. When you have finished drawing to one of the image buffers for one loop, then you are ready to display its result to the screen for the user. <code>al_flip_display</code> is called to swap the two image buffers around so that the first image buffer is now displayed to the user while the second image buffer becomes the one you will draw on. Failing to call this function will result in only the single, blank image buffer being shown on the screen. <code c>al_rest(10.0);</code> Here we rest the program for 10 seconds. **al_rest** takes a floating point integer specifying how many seconds to sleep. Using any valid floating point number is valid, including numbers less than 1.0. Allegro will attempt to sleep for the amount of time specified, but it does not have perfect accuracy. <code c>al_destroy_display(display);</code> This function destroys our display and frees the memory and should be called when you are about to shut down the program. And that concludes our basic introduction to Allegro 5 displays. [[allegro:start|Sommaire]] >> [[allegro:events|suite]]
