[A5] al_get

Ninjarobot

Does al_get_pixel return the pixel's colour in "ffffff" format?
If so how can I compare the colour this function returns with another hex colour?
I've tried:

#SelectExpand
 1if( (al_get_pixel(canvas,SCREEN_W/2,SCREEN_H/2) ) =="ffcc66")

and it gives me :"error: no match for 'operator==' in 'al_get_pixel(canvas, 320, 240) == "ffcc66"

I am trying to compare the colour of a target pixel and if it's X to paint red but if it's anything else to paint a sand-ish colour. Another question I have is if it's possible to use al_get_pixel on my canvas without making ALLEGRO_BITMAP canvas a global. I tried to use a reference but made it worse.

Thanks in advance.

#SelectExpand
   1#include <stdio.h>
   2#include <allegro5/allegro.h>
   3#include <allegro5/allegro_primitives.h>
   4#include <allegro5/allegro_color.h>
   5
   6
   7
   8/* constants and definitions */
   9
  10const int SCREEN_W = 640;
  11const int SCREEN_H = 480;
  12const float FPS = 60;
  13const int paddle_height = 96;
  14const int paddle_width = 16;
  15const int bouncer_size = 16;
  16const int cursor_size=18;
  17ALLEGRO_BITMAP *canvas= NULL;
  18
  19enum MYKEYS {
  20    KEY_UP, KEY_DOWN, KEY_W, KEY_S,KEY_A,KEY_D,KEY_SPACE,KEY_P
  21};
  22
  23/* functions */
  24
  25void draw_cursor(float x,float y)
  26{
  27  al_draw_circle(x , y, cursor_size, al_color_html("ff0000"), 2.0);
  28}
  29
  30void drop_sand(float x,float y)
  31{ if((al_get_pixel(canvas,SCREEN_W/2,SCREEN_H/2))=="ffcc66")
  32   {
  33    al_draw_filled_circle( x, y, cursor_size-3, al_color_html("ffff66"));
  34   }
  35
  36  else
  37  al_draw_filled_circle( x, y, cursor_size-3, al_color_html("ffcc66"));
  38
  39
  40
  41}
  42
  43
  44
  45void draw_ball(float x, float y)
  46{
  47  // fill
  48  al_draw_filled_circle(x, y, bouncer_size, al_color_html("6be97d"));
  49  // shadow
  50  al_draw_filled_circle(x+bouncer_size/4, y+bouncer_size/4, bouncer_size/3*2, al_color_html("59ce76"));
  51  // shine
  52  al_draw_filled_circle(x-bouncer_size/3, y-bouncer_size/3, bouncer_size/4, al_color_html("9bffaa"));
  53}
  54
  55
  56
  57
  58int main(int argc, char **argv)
  59{
  60    ALLEGRO_DISPLAY *display = NULL;
  61    ALLEGRO_EVENT_QUEUE *event_queue = NULL;
  62    ALLEGRO_TIMER *timer = NULL;
  63    ALLEGRO_BITMAP *sand = NULL;
  64    ALLEGRO_BITMAP *bouncer = NULL;
  65    ALLEGRO_BITMAP *cursor= NULL;
  66
  67
  68
  69    float bouncer_x = SCREEN_W / 2.0 - bouncer_size / 2.0;
  70    float bouncer_y = SCREEN_H / 2.0 - bouncer_size / 2.0;
  71    float bouncer_dx = 4.0, bouncer_dy = -4.0;
  72
  73    float cursor_x=(SCREEN_W / 2.0);
  74    float cursor_y=(SCREEN_H / 2.0);
  75
  76    bool key[8] = {false, false, false, false, false, false, false, false};
  77    bool redraw = true;
  78    bool doexit = false;
  79
  80    if(!al_init()) {
  81  fprintf(stderr, "failed to initialized allegro\n");
  82  return -1;
  83    }
  84
  85    if(!al_install_keyboard()) {
  86  fprintf(stderr, "failed to install keyboard\n");
  87  return -1;
  88    }
  89
  90
  91  al_init_primitives_addon();
  92
  93  al_set_new_display_option(ALLEGRO_SAMPLE_BUFFERS, 1, ALLEGRO_SUGGEST);
  94  al_set_new_display_option(ALLEGRO_SAMPLES, 4, ALLEGRO_SUGGEST);
  95
  96
  97    //initialize display (w, h)
  98    display = al_create_display(SCREEN_W, SCREEN_H);
  99    if(!display) {
 100  fprintf(stderr, "failed to create display\n");
 101  return -1;
 102    }
 103
 104    timer = al_create_timer(1.0/FPS);
 105    if(!timer) {
 106  fprintf(stderr, "failed to create timer\n");
 107  return -1;
 108    }
 109
 110     draw_cursor(300,200);
 111
 112
 113
 114    cursor = al_create_bitmap(cursor_size,cursor_size);
 115    sand = al_create_bitmap(cursor_size-3,cursor_size-3);
 116    bouncer = al_create_bitmap(bouncer_size, bouncer_size);
 117    canvas = al_create_bitmap(SCREEN_W, SCREEN_H);
 118
 119
 120    if(!bouncer) {
 121  fprintf(stderr, "failed to create bouncer bitmap\n");
 122  return -1;
 123    }
 124
 125
 126
 127    al_set_target_bitmap(bouncer);
 128    al_clear_to_color(al_map_rgb (0,0,0));
 129    al_set_target_bitmap(cursor);
 130    al_clear_to_color(al_map_rgb (0,0,0));
 131    al_set_target_bitmap(canvas);
 132    al_clear_to_color(al_map_rgb(0,0,0));
 133
 134
 135    al_set_target_bitmap(al_get_backbuffer(display));
 136
 137    event_queue = al_create_event_queue();
 138    if(!event_queue) {
 139  fprintf(stderr, "failed to create event queue\n");
 140  return -1;
 141    }
 142
 143    al_register_event_source(event_queue, al_get_display_event_source(display));
 144
 145    al_register_event_source(event_queue, al_get_timer_event_source(timer));
 146
 147    al_register_event_source(event_queue, al_get_keyboard_event_source());
 148
 149    al_clear_to_color(al_map_rgb(0, 0, 0));
 150
 151    al_flip_display();
 152
 153    al_start_timer(timer);
 154
 155    while(!doexit)
 156    {
 157  ALLEGRO_EVENT ev;
 158
 159  al_wait_for_event(event_queue, &ev);
 160
 161  if(ev.type == ALLEGRO_EVENT_TIMER) {
 162
 163      //DROP SAND
 164      if (key[KEY_SPACE]==true)
 165      {
 166          al_set_target_bitmap(canvas);
 167          drop_sand(cursor_x, cursor_y);
 168          al_set_target_bitmap(al_get_backbuffer(display));
 169          redraw = true;
 170
 171      }
 172
 173      //CURSOR
 174      if (key[KEY_W] && cursor_y >= 22.0)
 175      {
 176       cursor_y -= 4.0;
 177      }
 178      if(key[KEY_S] && cursor_y <= SCREEN_H - cursor_size - 4.0)
 179      {
 180       cursor_y += 4.0;
 181      }
 182      if(key[KEY_A] && cursor_x >= 22.0)
 183      {
 184       cursor_x -= 4.0;
 185      }
 186      if(key[KEY_D] && cursor_x <= SCREEN_W - cursor_size - 4.0)
 187      {
 188       cursor_x += 4.0;
 189      }
 190      //CURSOR
 191
 192      //logic for the bouncer
 193      if(bouncer_x < 0 || bouncer_x > SCREEN_W - bouncer_size) {
 194    bouncer_dx = -bouncer_dx;
 195      }
 196
 197      if(bouncer_y < 0 || bouncer_y > SCREEN_H - bouncer_size) {
 198    bouncer_dy = -bouncer_dy;
 199      }
 200
 201
 202
 203      bouncer_x += bouncer_dx;
 204      bouncer_y += bouncer_dy;
 205
 206      redraw = true;
 207  }
 208
 209  else if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
 210      break;
 211  }
 212
 213  else if(ev.type == ALLEGRO_EVENT_KEY_DOWN) {
 214      switch(ev.keyboard.keycode) {
 215    case ALLEGRO_KEY_UP:
 216        key[KEY_UP] = true;
 217        break;
 218
 219    case ALLEGRO_KEY_DOWN:
 220        key[KEY_DOWN] = true;
 221        break;
 222
 223    case ALLEGRO_KEY_W:
 224        key[KEY_W] = true;
 225        break;
 226
 227    case ALLEGRO_KEY_S:
 228        key[KEY_S] = true;
 229        break;
 230
 231    case ALLEGRO_KEY_A:
 232        key[KEY_A] = true;
 233        break;
 234
 235    case ALLEGRO_KEY_D:
 236        key[KEY_D] = true;
 237        break;
 238
 239    case ALLEGRO_KEY_SPACE:
 240        key[KEY_SPACE] = true;
 241        break;
 242      }
 243  }
 244
 245  else if(ev.type == ALLEGRO_EVENT_KEY_UP) {
 246      switch(ev.keyboard.keycode) {
 247    case ALLEGRO_KEY_UP:
 248        key[KEY_UP] = false;
 249        break;
 250
 251    case ALLEGRO_KEY_DOWN:
 252        key[KEY_DOWN] = false;
 253        break;
 254
 255    case ALLEGRO_KEY_W:
 256        key[KEY_W] = false;
 257        break;
 258
 259    case ALLEGRO_KEY_S:
 260        key[KEY_S] = false;
 261        break;
 262
 263    case ALLEGRO_KEY_A:
 264        key[KEY_A] = false;
 265        break;
 266
 267    case ALLEGRO_KEY_D:
 268        key[KEY_D] = false;
 269        break;
 270
 271    case ALLEGRO_KEY_SPACE:
 272        key[KEY_SPACE] = false;
 273        break;
 274
 275    case ALLEGRO_KEY_ESCAPE:
 276        doexit = true;
 277        break;
 278      }
 279  }
 280
 281  if(redraw && al_is_event_queue_empty(event_queue)) {
 282      redraw = false;
 283      al_set_target_bitmap(cursor);
 284      al_clear_to_color(al_map_rgb(0,0,0));
 285
 286      al_set_target_bitmap(bouncer);
 287      al_clear_to_color(al_map_rgb(0,0,0));
 288
 289
 290
 291
 292      al_set_target_bitmap(al_get_backbuffer(display));
 293      al_draw_bitmap(canvas, 0, 0, 0);    
 294      draw_cursor(cursor_x, cursor_y);   
 295      draw_ball(bouncer_x, bouncer_y);
 296
 297
 298
 299      al_rest(0.02);
 300
 301      al_flip_display();
 302  }
 303    }
 304    al_destroy_bitmap(cursor);
 305    al_destroy_bitmap(bouncer);
 306    al_destroy_bitmap(sand);
 307    al_destroy_timer(timer);
 308    al_destroy_display(display);
 309    al_destroy_event_queue(event_queue);
 310
 311    return 0;
 312}

Arthur Kalliokoski

A C compiler wants the '0x' prefix to denote a hexadecimal representation. And binary integers are just bits, the 0xFFFF whatever, vs 45093 is just a convenience for the human reader.

Matthew Leverton

Ninjarobot said:

Does al_get_pixel return the pixel's colour in "ffffff" format?

I don't know... let's check the documentation. That seems like a reasonable place for the answer to be.

Quote:

ALLEGRO_COLOR al_get_pixel(ALLEGRO_BITMAP *bitmap, int x, int y)

Looks like it returns a structure. Let's see what it looks like.

Quote:

An ALLEGRO_COLOR structure describes a color in a device independant way. Use al_map_rgb et al. and al_unmap_rgb et al. to translate from and to various color representations.

There's the answer.

kenmasters1976

al_get_pixel() returns an ALLEGRO_COLOR. You can use al_unmap_rgb() and then compare the individual color components.

Ninjarobot

I did read that part in the manual but I noticed al_unmap_rgb(and the spin-offs) is void which confuses me on how I am supposed to retrieve the colour let alone compare it. Sorry if I am missing something here.

Matthew Leverton

Note that you can click on any of the related discussions in the online manual to see how a function is used with some context.

unsigned char r, g, b;
al_unmap_rgb(col, &r, &g, &b);

if (r == 0xff && g == 0x00 && b == 0x00)
{
}

You could create a function:

bool cmp_color(ALLEGRO_COLOR col, unsigned int h)
{
  unsigned char r, g, b;
  al_unmap_rgb(col, &r, &g, &b);

  return r == ((h >> 16) & 0xff) && 
         g == ((h >> 8) & 0xff) && 
         b == h & 0xff;
}

if (cmp_color(c, 0xff0000))
{
}

Neil Roy

I used this to check for any colour other than black (all zeros which is transparent in my game). I'm looking for anything other than zero to show a collision (two coloured pixels occupying the same location on overlapping sprites). I chose memcmp(). This won't work in all circumstances, but it worked well here. ALLEGRO_COLOR simply holds RGBA values.

         // sample a pixel from each object
         pixel[0] = al_get_pixel(object1->img, (over_left-object1->x)+cx, (over_top-object1->y)+cy);
         pixel[1] = al_get_pixel(object2->img, (over_left-object2->x)+cx, (over_top-object2->y)+cy);


         // We'll compare the memory of our pixels to our transparent structure and see if we have a
         // collision.  If both memcmp() is true (non-zero) than we have a collision.
         if(memcmp(&pixel[0], &trans, sizeof(trans)) && memcmp(&pixel[1], &trans, sizeof(trans)))
         {
            collision=true;
            goto EXIT;
         }

Thread #606723. Printed from Allegro.cc