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  1. <HTML
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  4. >Event Examples</TITLE
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  39. >SDL Library Documentation</TH
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  54. >Chapter 4. Examples</TD
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  69. CLASS="SECT1"
  70. ><H1
  71. CLASS="SECT1"
  72. ><A
  73. NAME="GUIDEEVENTEXAMPLES"
  74. >Event Examples</A
  75. ></H1
  76. ><P
  77. ></P
  78. ><DIV
  79. CLASS="SECT2"
  80. ><H2
  81. CLASS="SECT2"
  82. ><A
  83. NAME="AEN408"
  84. >Filtering and Handling Events</A
  85. ></H2
  86. ><P
  87. ><PRE
  88. CLASS="PROGRAMLISTING"
  89. >#include <stdio.h>
  90. #include <stdlib.h>
  91.  
  92. #include "SDL.h"
  93.  
  94. /* This function may run in a separate event thread */
  95. int FilterEvents(const SDL_Event *event) {
  96.     static int boycott = 1;
  97.  
  98.     /* This quit event signals the closing of the window */
  99.     if ( (event->type == SDL_QUIT) && boycott ) {
  100.         printf("Quit event filtered out -- try again.\n");
  101.         boycott = 0;
  102.         return(0);
  103.     }
  104.     if ( event->type == SDL_MOUSEMOTION ) {
  105.         printf("Mouse moved to (%d,%d)\n",
  106.                 event->motion.x, event->motion.y);
  107.         return(0);    /* Drop it, we've handled it */
  108.     }
  109.     return(1);
  110. }
  111.  
  112. int main(int argc, char *argv[])
  113. {
  114.     SDL_Event event;
  115.  
  116.     /* Initialize the SDL library (starts the event loop) */
  117.     if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
  118.         fprintf(stderr,
  119.                 "Couldn't initialize SDL: %s\n", SDL_GetError());
  120.         exit(1);
  121.     }
  122.  
  123.     /* Clean up on exit, exit on window close and interrupt */
  124.     atexit(SDL_Quit);
  125.  
  126.     /* Ignore key events */
  127.     SDL_EventState(SDL_KEYDOWN, SDL_IGNORE);
  128.     SDL_EventState(SDL_KEYUP, SDL_IGNORE);
  129.  
  130.     /* Filter quit and mouse motion events */
  131.     SDL_SetEventFilter(FilterEvents);
  132.  
  133.     /* The mouse isn't much use unless we have a display for reference */
  134.     if ( SDL_SetVideoMode(640, 480, 8, 0) == NULL ) {
  135.         fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
  136.                         SDL_GetError());
  137.         exit(1);
  138.     }
  139.  
  140.     /* Loop waiting for ESC+Mouse_Button */
  141.     while ( SDL_WaitEvent(&event) >= 0 ) {
  142.         switch (event.type) {
  143.             case SDL_ACTIVEEVENT: {
  144.                 if ( event.active.state & SDL_APPACTIVE ) {
  145.                     if ( event.active.gain ) {
  146.                         printf("App activated\n");
  147.                     } else {
  148.                         printf("App iconified\n");
  149.                     }
  150.                 }
  151.             }
  152.             break;
  153.                     
  154.             case SDL_MOUSEBUTTONDOWN: {
  155.                 Uint8 *keys;
  156.  
  157.                 keys = SDL_GetKeyState(NULL);
  158.                 if ( keys[SDLK_ESCAPE] == SDL_PRESSED ) {
  159.                     printf("Bye bye...\n");
  160.                     exit(0);
  161.                 }
  162.                 printf("Mouse button pressed\n");
  163.             }
  164.             break;
  165.  
  166.             case SDL_QUIT: {
  167.                 printf("Quit requested, quitting.\n");
  168.                 exit(0);
  169.             }
  170.             break;
  171.         }
  172.     }
  173.     /* This should never happen */
  174.     printf("SDL_WaitEvent error: %s\n", SDL_GetError());
  175.     exit(1);
  176. }</PRE
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