游戏引擎Allegro之例子2

1.学习例子ex_bitmap_flip.c
2.一个显示位图翻转标志的例子

/* An example showing bitmap flipping flags, by Steven Wallace. */

#include 
#include 
#include 

#include "common.c"

/* Fire the update every 10 milliseconds. */
#define INTERVAL 0.01


float bmp_x = 200;   //起始坐标
float bmp_y = 200;   //起始坐标
float bmp_dx = 96;   //水平速度
float bmp_dy = 96;   //垂直速度
int bmp_flag = 0;

/* Updates the bitmap velocity, orientation and position. */
static void update(ALLEGRO_BITMAP *bmp)
{
   ALLEGRO_BITMAP *target = al_get_target_bitmap();   /*全屏位图*/
   int display_w = al_get_bitmap_width(target);
   int display_h = al_get_bitmap_height(target);
   int bitmap_w = al_get_bitmap_width(bmp);
   int bitmap_h = al_get_bitmap_height(bmp);

   bmp_x += bmp_dx * INTERVAL;
   bmp_y += bmp_dy * INTERVAL;

   /* Make sure bitmap is still on the screen. */
/*ALLEGRO_FLIP_VERTICAL=2*/
/*~ALLEGRO_FLIP_VERTICAL=01*/
/*bmp_flag &= 01就是把bit2变0*/
/*将垂直翻转状态置0*/
/*结果就是在上边时候垂直不翻转*/
   if (bmp_y < 0) {
      bmp_y = 0;
      bmp_dy *= -1;
      bmp_flag &= ~ALLEGRO_FLIP_VERTICAL; /*2,1,0*/
      //printf("bmp_y ALLEGRO_FLIP_VERTICAL=%d bmp_flag=%d\n", ALLEGRO_FLIP_VERTICAL, bmp_flag);
   }
/*ALLEGRO_FLIP_HORIZONTAL=1*/
/*~ALLEGRO_FLIP_HORIZONTAL=0*/
/*bmp_flag &= 0就是把bit1变0*/
/*将水平翻转状态置0*/
/*结果就是在左边时候水平不翻转*/
   if (bmp_x < 0) {
      bmp_x = 0;
      bmp_dx *= -1;
      bmp_flag &= ~ALLEGRO_FLIP_HORIZONTAL;
      //printf("bmp_x  ALLEGRO_FLIP_HORIZONTAL=%d bmp_flag=%d\n", ALLEGRO_FLIP_HORIZONTAL, bmp_flag);
   }
/*ALLEGRO_FLIP_VERTICAL=2*/
/*bmp_flag |= 10就是把bit2变1*/
/*将垂直翻转状态置1*/
/*结果就是在下边时候垂直翻转*/
   if (bmp_y > display_h - bitmap_h) {
      bmp_y = display_h - bitmap_h;
      bmp_dy *= -1;
      bmp_flag |= ALLEGRO_FLIP_VERTICAL;
      //printf("bmp_y2  ALLEGRO_FLIP_VERTICAL=%d bmp_flag=%d\n", ALLEGRO_FLIP_VERTICAL, bmp_flag);
   }

/*ALLEGRO_FLIP_HORIZONTAL=1*/
/*bmp_flag |= 1就是把bit1变1*/
/*将水平翻转状态置1*/
/*结果就是在右边时候水平翻转*/
   if (bmp_x > display_w - bitmap_w) {
      bmp_x = display_w - bitmap_w;
      bmp_dx *= -1;
      bmp_flag |= ALLEGRO_FLIP_HORIZONTAL;
      //printf("bmp_x2  ALLEGRO_FLIP_HORIZONTAL=%d bmp_flag=%d\n", ALLEGRO_FLIP_HORIZONTAL, bmp_flag);
   }
}


int main(int argc, char **argv)
{
   ALLEGRO_DISPLAY *display;
   ALLEGRO_TIMER *timer;
   ALLEGRO_EVENT_QUEUE *queue;
   ALLEGRO_BITMAP *bmp;
   ALLEGRO_BITMAP *mem_bmp;
   ALLEGRO_BITMAP *disp_bmp;
   ALLEGRO_FONT *font;
   char *text;
   bool done = false;
   bool redraw = true;

   /* Silence unused arguments warnings. */
   (void)argc;
   (void)argv;

   if (!al_init()) {
      abort_example("Failed to init Allegro.\n");
   }

   /* Initialize the image addon. Requires the allegro_image addon
    * library.
    */
   if (!al_init_image_addon()) {
      abort_example("Failed to init IIO addon.\n");
   }

   /* Initialize the image font. Requires the allegro_font addon
    * library.
    */
   al_init_font_addon();
   init_platform_specific(); /* Helper functions from common.c. */

   /* Create a new display that we can render the image to. */
   display = al_create_display(640, 480);
   if (!display) {
      abort_example("Error creating display.\n");
   }

   /* Allegro requires installing drivers for all input devices before
    * they can be used.
    */
   if (!al_install_keyboard()) {
      abort_example("Error installing keyboard.\n");
   }

   /* Loads a font from disk. This will use al_load_bitmap_font if you
    * pass the name of a known bitmap format, or else al_load_ttf_font.
    */
   font = al_load_font("data/fixed_font.tga", 0, 0);
   if (!font) {
      abort_example("Error loading data/fixed_font.tga\n");
   }

   bmp = disp_bmp = al_load_bitmap("data/mysha.pcx");
   if (!bmp) {
      abort_example("Error loading data/mysha.pcx\n");
   }
   text = "Display bitmap (space to change)";

/*创建驻留在系统内存中的位图*/
   al_set_new_bitmap_flags(ALLEGRO_MEMORY_BITMAP);
   mem_bmp = al_load_bitmap("data/mysha.pcx");
   if (!mem_bmp) {
      abort_example("Error loading data/mysha.pcx\n");
   }

/*创建定时器*/
   timer = al_create_timer(INTERVAL);

   queue = al_create_event_queue();
   al_register_event_source(queue, al_get_keyboard_event_source());
   al_register_event_source(queue, al_get_timer_event_source(timer));
   al_register_event_source(queue, al_get_display_event_source(display));

/*启动定时器*/
   al_start_timer(timer);

   /* Default premultiplied aplha blending. */
   al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_INVERSE_ALPHA);

   /* Primary 'game' loop. */
   while (!done) {
      ALLEGRO_EVENT event;

      /* If the timer has since been fired and the queue is empty, draw.*/
      if (redraw && al_is_event_queue_empty(queue)) {
         update(bmp);
         /* Clear so we don't get trippy artifacts left after zoom. */
         al_clear_to_color(al_map_rgb_f(0, 0, 0));
         al_draw_tinted_bitmap(bmp, al_map_rgba_f(1, 1, 1, 0.5),
            bmp_x, bmp_y, bmp_flag);   
            /*bmp_flag=0表示不翻转,*/
            /*bmp_flag=1表示ALLEGRO_FLIP_HORIZONTAL,水平翻转*/
            /*bmp_flag=2表示ALLEGRO_FLIP_VERTICAL,垂直翻转*/
           /*bmp_flag=3表示ALLEGRO_FLIP_HORIZONTAL+ALLEGRO_FLIP_VERTICAL,水平翻转+垂直翻转*/
         al_draw_text(font, al_map_rgba_f(1, 1, 1, 0.5), 0, 0, 0, text);
         al_flip_display();
         redraw = false;
      }

      al_wait_for_event(queue, &event);
      switch (event.type) {
         case ALLEGRO_EVENT_KEY_DOWN:
            if (event.keyboard.keycode == ALLEGRO_KEY_ESCAPE)
               done = true;
            else if (event.keyboard.keycode == ALLEGRO_KEY_SPACE) {
               /* Spacebar toggles whether render from a memory bitmap
                * or display bitamp.
                */
               if (bmp == mem_bmp) {
                  bmp = disp_bmp;
                  text = "Display bitmap (space to change)";
               }
               else {
                  bmp = mem_bmp;
                  text = "Memory bitmap (space to change)";
               }
            }
               
            break;

         case ALLEGRO_EVENT_DISPLAY_CLOSE:
            done = true;
            break;

         case ALLEGRO_EVENT_TIMER:
            redraw = true;
            break;
      }
   }

   al_destroy_bitmap(bmp);

   return 0;
}

/* vim: set sts=3 sw=3 et: */

3.运行效果

1AFF2873-C3E1-46D7-8311-4A2DF57867FA.png

4.代码地址