2D Platformer Collision Handling
- by defender-zone
Hello, everyone!
I am trying to create a 2D platformer (Mario-type) game and I am some having some issues with handling collisions properly. I am writing this game in C++, using SDL for input, image loading, font loading, etcetera. I am also using OpenGL via the FreeGLUT library in conjunction with SDL to display graphics.
My method of collision detection is AABB (Axis-Aligned Bounding Box), which is really all I need to start with. What I need is an easy way to both detect which side the collision occurred on and handle the collisions properly. So, basically, if the player collides with the top of the platform, reposition him to the top; if there is a collision to the sides, reposition the player back to the side of the object; if there is a collision to the bottom, reposition the player under the platform.
I have tried many different ways of doing this, such as trying to find the penetration depth and repositioning the player backwards by the penetration depth. Sadly, nothing I've tried seems to work correctly. Player movement ends up being very glitchy and repositions the player when I don't want it to. Part of the reason is probably because I feel like this is something so simple but I'm over-thinking it.
If anyone thinks they can help, please take a look at the code below and help me try to improve on this if you can. I would like to refrain from using a library to handle this (as I want to learn on my own) or the something like the SAT (Separating Axis Theorem) if at all possible. Thank you in advance for your help!
void world1Level1CollisionDetection()
{
for(int i; i < blocks; i++)
{
if (de2dCheckCollision(ball,block[i],0.0f,0.0f)==true)
{
int up = 0;
int left = 0;
int right = 0;
int down = 0;
if(ball.coords[0] < block[i].coords[0] && block[i].coords[0] < ball.coords[2] && ball.coords[2] < block[i].coords[2])
{
left = 1;
}
if(block[i].coords[0] < ball.coords[0] && ball.coords[0] < block[i].coords[2] && block[i].coords[2] < ball.coords[2])
{
right = 1;
}
if(ball.coords[1] < block[i].coords[1] && block[i].coords[1] < ball.coords[3] && ball.coords[3] < block[i].coords[3])
{
up = 1;
}
if(block[i].coords[1] < ball.coords[1] && ball.coords[1] < block[i].coords[3] && block[i].coords[3] < ball.coords[3])
{
down = 1;
}
cout << left << ", " << right << ", " << up << ", " << down << ", " << endl;
if (left == 1)
{
ball.coords[0] = block[i].coords[0] - 16.0f;
ball.coords[2] = block[i].coords[0] - 0.0f;
}
if (right == 1)
{
ball.coords[0] = block[i].coords[2] + 0.0f;
ball.coords[2] = block[i].coords[2] + 16.0f;
}
if (down == 1)
{
ball.coords[1] = block[i].coords[3] + 0.0f;
ball.coords[3] = block[i].coords[3] + 16.0f;
}
if (up == 1)
{
ball.yspeed = 0.0f;
ball.gravity = 0.0f;
ball.coords[1] = block[i].coords[1] - 16.0f;
ball.coords[3] = block[i].coords[1] - 0.0f;
}
}
if (de2dCheckCollision(ball,block[i],0.0f,0.0f)==false)
{
ball.gravity = -0.5f;
}
}
}
To explain what some of this code means:
The blocks variable is basically an integer that is storing the amount of blocks, or platforms. I am checking all of the blocks using a for loop, and the number that the loop is currently on is represented by integer i.
The coordinate system might seem a little weird, so that's worth explaining.
coords[0] represents the x position (left) of the object (where it starts on the x axis).
coords[1] represents the y position (top) of the object (where it starts on the y axis).
coords[2] represents the width of the object plus coords[0] (right).
coords[3] represents the height of the object plus coords[1] (bottom).
de2dCheckCollision performs an AABB collision detection.
Up is negative y and down is positive y, as it is in most games.
Hopefully I have provided enough information for someone to help me successfully. If there is something I left out that might be crucial, let me know and I'll provide the necessary information. Finally, for anyone who can help, providing code would be very helpful and much appreciated.
Thank you again for your help!
