OpenGL - drawing objects using text file - c++

Question

I have loaded an array from a text file, which contains positions of objects, and it looks like this:
0,0,0,5
0,5,0,0
0,0,5,0
0,5,5,0
The object looks like this:
struct object
{
int x, y, value;
}
Where x,y are coordinates, and value is 1 or 0 (it tells if an object was "picked", all objects have 1 at the beginning). Objects are stored in an array object obj_array[5].
To draw them, I use this function:
(BOARD_Y and BOARD_Y is size of the array, here is 4x4)
void draw_board(){
for (int iy = 0; iy < BOARD_Y; iy++) {
for (int ix = 0; ix < BOARD_X; ix++) {
if ( (board[iy][ix] == 5) )
{
glPushMatrix();
glTranslatef( ix, iy, 0 );
glutSolidCube(1);
glPopMatrix();
}
}
}
}
And it draws all of them perfectly. But I want to skip drawing an object, if its value is 0 (the object was picked by a player). How can I do this?

Answer 1

Okey, I can see what's going on; you've complicated the things a bit. There's no way to access the arbitrary object just from this loop, apart from pretty stupid comparison of position:
if ( (board[iy][ix] == 5) ) {
for (auto const& obj : objects) {
if (obj.x == ix && obj.y == iy) {
// obj is the object in given position
// ...
break;
}
}
}
Don't do that.
Instead either store some reference to the objects on the board. By reference I mean (not limited to!):
An unique object ID
Pointer to the object
Then, you will be able to access the object residing on given tile much faster and easier. If you want examples, drop a comment, but I think both options are fairly easy to implement.
If you still want to hold these "5" inside, change board to array of structs. And oh, please use std::array instead of int**.
Here's the example
using id_t = unsigned;
std::map<id_t, object> objects;
constexpr std::size_t size_x = 4, size_y = 4;
std::array<id_t, size_x * size_y> board;
Let's assume that id equal to 0 means that the object is not there.
Now you can access the specific object by:
unsigned x, y;
id_t obj_id = board[x + size_x * y];
if (obj_id != 0) // is there any object?
if (objects[obj_id].value != 0) // is its value equal to 0?
// ...
And set it by board[...] = obj;
Easy way to generate unique id for every object is just to increment the counter.
id_t last_id = 1;
objects[last_id++] = obj_id;