Collision detection, Arrays and the state of the union

Collision detection, Arrays and the state of the union

joshua.tilson

Member #7,552

July 2006

Good morning!

I have a couple of questions, one simple, one not so simple. Any way, I have been working with arrays to represent tile maps.

 int map[32][32];
for (int i=0;i<32;i++){
for (int j=1;j<32;j++){
map<i>[j] = rand()%2;}}

Now here i can easily set all my array elements to random numbers (this reflects my next question), But How do i initialize the array with all 1024 elements set as I want them? IE: trying to plan out a tilemap that isn't random?? I have seen examples like

 int map[32][32] = {{1,1,1,1,1,1,1,1,1,1}}
{{1,1,1,1,1,1,1,1}}
{{.........}}

But that has never worked for me i always get a compile error!

The next subject i have come to is collision detection, this seems to be the hardest for me so far. LELete clarify, When I adhad aet map in my pong game, i could easily do the cocollisionetection because i always knew where the walls and paddles would be, but with a random tileset like my above example, how do i tell where the tiles are in my code?
What i mean is this, i have the code that makes a ball move, therefore i will always be able to check the position of the ball, but how do i detect for the placement of random collidable tiles?

Thanks for stopping by and taking a look!

Josh

Archon

Member #4,195

January 2004

Quote:

But How do i initialize the array with all 1024 elements set as I want them?

'new' them and then iterate through them.

Quote:

but with a random tileset like my above example, how do i tell where the tiles are in my code?

Use position variables to represent where you are colliding. Then match the position of your chracter against the tilemap.

LennyLen

Member #5,313

December 2004

Quote:

But that has never worked for me i always get a compile error!

Well, in the example you just gave, you missed the commas between the sets. Try compiling the following and see what happens.

1#include <stdio.h>
2 
3int map[10][10] = 
{{1, 2, 3, 2, 1, 2, 3, 6, 3, 5}, 
{8, 2, 3, 2, 1, 2, 3, 6, 3, 5},
{1, 2, 3, 2, 6, 2, 3, 6, 3, 5},
{2, 2, 4, 2, 1, 4, 3, 6, 1, 5},
{1, 2, 8, 2, 1, 2, 3, 6, 3, 5},
{1, 2, 3, 2, 1, 2, 3, 3, 5, 8},
{1, 2, 3, 2, 1, 2, 3, 6, 3, 5},
{8, 2, 3, 8, 1, 2, 3, 9, 3, 5},
{1, 2, 3, 2, 1, 2, 3, 6, 3, 5},
{1, 2, 3, 2, 1, 2, 3, 6, 3, 5}};

15int x, y;

17int main() {

for (x = 0; x < 10; x++) {
  
  for (y = 0; y < 10; y++) {
    
    printf("%d ", map[x][y]);
    
  }
  
  printf("\n");
  
}

return 0;

33}

By the way, this is a valid way of assing values to arrays, but it means you have to recompile your game every time you change a map. It's better to load the values from a file.

joshua.tilson

Member #7,552

July 2006

Lenny,

Perfect thank you, The previous examples i had seen had shown ; instead of , So that explains my problem there.

well let me show, whoever is interested, My lame attempt at collision detection, it works about 15%...

1/* game design and psuedo code
2**  initialize game
3**   set up screen
4**  draw paddle, ball and bricks
5**  player launches ball
6**   if ball is not below paddle
7**    then move ball
8**   else if ball collides with brick
9**        then remove brick and add points
10**   check to see if ball is below paddle or if all bricks are gone
11**         then end game.
12**
13**
14** drawscreen()
15** collision()
16** checkball pos()
17**
18** screen is 20x15tiles  X,Y
19*/
20 
21#include <allegro.h>
22 
23BITMAP *ball;
24BITMAP *paddle;
25BITMAP *background;
26BITMAP *brick;
27BITMAP *buf;
28 
29const int MIN_BALL_X = 5;
30const int MAX_BALL_X = 635;
31const int MIN_BALL_Y = 0;
32const int MAX_BALL_Y = 480;
33 
34int paddleX = 275;
35int padTemp;
36int ballX, ballY;
37int dx = 0;
38int dy = 0;
39int ballTempX, ballTempY;
40int brickMap[20][13];
41 
42bool ballOn = true;
43 
44void init();
45void deinit();
46void drawScreen();
47int collide();
48bool movePaddle();
49void moveBall();
50void startBall();
51void updateScreen();
52 
53 
54 
55int main() {
56  init();
57    drawScreen();
58  while (!key[KEY_ESC]) {
59  movePaddle();
60    updateScreen();
61    moveBall();
62  }
63 
64  deinit();
65  return 0;
66}
67END_OF_MAIN()
68 
69 
70    
71void drawScreen() {
72     background = load_bitmap("background.bmp", NULL);
73     paddle = load_bitmap("paddle.bmp", NULL);
74     ball = load_bitmap("ball.bmp", NULL);
75     brick = load_bitmap("brick.bmp",NULL);
76     draw_sprite(screen, background, 0, 0);
77     draw_sprite(screen, paddle, 275, 450);
78     draw_sprite(screen, ball, 314, 438);
79     
80    
81     for (int i=0; i <20; i++)
82        for (int j=0; j <13; j++)
83         { if (brickMap<i>[j] == 1) 
84           draw_sprite(screen, brick, i * 32, j * 32); 
85         }
86         rest(5);
87     }
88     
89bool movePaddle() {
90     if (key[KEY_LEFT] && paddleX != 0)
91        {--paddleX;
92        if(ballOn ==true){ --ballX;}
93        }
94     else if (key[KEY_RIGHT] && paddleX + 90 != 640)
95          { ++paddleX;
96          if(ballOn == true) {++ballX;}
97           }
98     else if (key[KEY_SPACE] && ballOn == true) {
99          startBall();
100          ballOn=false;
101          }
102     return true;
103     }
104     
105void startBall(){
106     dx= -1;
107     dy= 3;
108     }
109     
110void moveBall() {
111     int ballCollisionX, ballCollisionY;
112     ballTempX=ballX;
113     ballTempY=ballY;
114   
115   ballCollisionX = ballX / 32;
116   ballCollisionY = ballY /32;
117   if (brickMap[ballCollisionX][ballCollisionY] == 1)
118      {dy = -dy;}    
119 if (dy > 0 && ballX > paddleX && ballX < paddleX + 90 && ballY == 438) 
120       {
121        dy = -dy;  }
122 else
123 
124     if (dx < 0)
125     {
126      if (ballX + dx > MIN_BALL_X)
127      {
128    ballX += dx;
129      }
130      else
131        {
132    ballX = 2 * MIN_BALL_X - dx - ballX;
133    dx = -dx;
134        }
135      }
136      
137      else // dx > 0
138      {
139           if (ballX + dx < MAX_BALL_X)
140         {
141       ballX += dx;
142         }
143         else
144         {
145           ballX = 2 * MAX_BALL_X - dx - ballX;
146           dx = -dx;
147          }
148       } 
149 
150       if (dy < 0 )
151       {
152        if (ballY + dy > MIN_BALL_Y )
153        {
154          ballY += dy;
155          }
156          else
157        {
158        ballY = 2 * MIN_BALL_Y - dy - ballY;
159        dy = -dy;
160        }
161       }
162       
163       else // dy > 0
164       {
165          if (ballY + dy < MAX_BALL_Y)
166          {
167        ballY += dy;
168          }
169          else
170          {
171        ballY = 2 * MAX_BALL_Y - dy - ballY;
172        dy = -dy;
173          }
174         
175         }
176      
177}
178                
179void updateScreen() {
180     padTemp= paddleX;
181     buf = create_bitmap(90,26);
182     draw_sprite(buf, paddle, 0, 0);
183     draw_sprite(screen, buf, paddleX, 450);
184     destroy_bitmap(buf);
185     buf = create_bitmap(12,12);
186     draw_sprite(buf, ball, 0,0 );
187     draw_sprite(screen, buf, ballX, ballY);
188     rest(5);
189     }
190void init() {
191  int depth, res;
192  allegro_init();
193  depth = desktop_color_depth();
194  if (depth == 0) depth = 32;
195  set_color_depth(depth);
196  res = set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0);
197  if (res != 0) {
198    allegro_message(allegro_error);
199    exit(-1);
200  }
201 
202  install_timer();
203  install_keyboard();
204  install_mouse();
205  
206  ballX= 314;
207  ballY= 438;
208    for(int i=0; i < 20; i++)
209       for(int j=0; j < 13; j++)
210          brickMap<i>[j] = rand()%2;
211    /* add other initializations here */
212}
213 
214void deinit() {
215  clear_keybuf();
216  /* add other deinitializations here */
217}

in particular it is this bit of code that does 'it' wwhateverit is

ballCollisionX = ballX / 32;
   ballCollisionY = ballY /32;
   if (brickMap[ballCollisionX][ballCollisionY] == 1)
      {dy = -dy;}

I take my ball's x and y and divide them by 32, in theory this gives me a whole number 1,2 etc since my tile size is 32x32. I then plug the divdividedy into the tilemap to see if it equals a collidable tile, if it does i change the direction of the ball. Obviously this is very rudimentary and imperfect...

I atatched the BMPs i am using so you can compile and check out exactly what it is doing...

thanks again!

EDIT: i guess one solution would to be ta make sure that the ballCOllisionX and Y are divisible by 1 to make sure they are whoel numbers? i can't use !/ i get a compile error /! works untill i run the program then it crashes!

EDIT 2: wait an int has to be a whol enumber doesn't it, thats why we have floating point variables.... Hmmm so then back to the drawing board on that one!