My 2D collision code does not work as expected. How do I fix it?
- by farmdve
I have a simple 2D game with a tile-based map. I am new to game development, I followed the LazyFoo tutorials on SDL.
The tiles are in a bmp file, but each tile inside it corresponds to an internal number of the type of tile(color, or wall).
The game is simple, but the code is a lot so I can only post snippets.
// Player moved out of the map
if((player.box.x < 0))
player.box.x += GetVelocity(player, 0);
if((player.box.y < 0))
player.box.y += GetVelocity(player, 1);
if((player.box.x > (LEVEL_WIDTH - DOT_WIDTH)))
player.box.x -= GetVelocity(player, 0);
if((player.box.y > (LEVEL_HEIGHT - DOT_HEIGHT)))
player.box.y -= GetVelocity(player, 1);
// Now that we are here, we check for collisions
if(touches_wall(player.box))
{
if(player.box.x < player.prev_x)
{
player.box.x += GetVelocity(player, 0);
}
if(player.box.x > player.prev_x)
{
player.box.x -= GetVelocity(player, 0);
}
if(player.box.y < player.prev_y)
{
player.box.y += GetVelocity(player, 1);
}
if(player.box.y > player.prev_y)
{
player.box.y -= GetVelocity(player, 1);
}
}
player.prev_x = player.box.x;
player.prev_y = player.box.y;
Let me explain, player is a structure with the following contents
typedef struct {
Rectangle box; //Player position on a map(tile or whatever).
int prev_x, prev_y; // Previous positions
int key_press[3]; // Stores which key was pressed/released. Limited to three keys. E.g Left,right and perhaps jump if possible in 2D
int velX, velY; // Velocity for X and Y coordinate.
//Health
int health;
bool main_character;
uint32_t jump_ticks;
} Player;
And Rectangle is just a typedef of SDL_Rect. GetVelocity is a function that according to the second argument, returns the velocity for the X or Y axis.
This code I have basically works, however inside the if(touches_wall(player.box)) if statement, I have 4 more.
These 4 if statements are responsible for detecting collision on all 4 sides(up,down,left,right). However, they also act as a block for any other movement.
Example: I move down the object and collide with the wall, as I continue to move down and still collide with the wall, I wish to move left or right, which is indeed possible(not to mention in 3D games), but remember the 4 if statements? They are preventing me from moving anywhere.
The original code on the LazyFoo Productions website has no problems, but it was written in C++, so I had to rewrite most of it to work, which is probably where the problem comes from. I also use a different method of moving, than the one in the examples.
Of course, that was just an example. I wish to be able to move no matter at which wall I collide. Before this bit of code, I had another one that had more logic in there, but it was flawed.
