collision doc

Collisions

Collision function

This is the first draft for a collision function.

Label:

collision

Parameters:

Label	Type	Size/Struct	Description
collision_.p.1	fixed address	point	Left Top corner of the first element checked
collision_.p.2	fixed address	point	Left Top corner of the second element checked
collision_.hitbox1	fixed address	1 byte	Id of the hitbox of the first element checked
collision_.hitbox2	fixed address	1 byte	Id of the hitbox of the second element checked

Return:

Label	Type	Size	Description
a	register	1 byte	1 if collision detected, 0 else.

Modified values:

Label	Type	Size/Struc
a	register	1 byte
hl	register	2 bytes
collision_.p.1	fixed address	point
collision_.p.2	fixed address	point

Global variables used

Label	Size	Description
hitboxs_width[2]	2*1 bytes	Array of the hitboxes width
hitboxs_height[2]	2*1 bytes	Array of the hitboxes height

Global structs used

point

Label	Size	Description
x	1 byte	abscissa of the point
y	1 byte	ordinate of the point

Reserved memory:

Label	Size/Struct	Description
collision_.p.1	point	Left Top corner of the first element checked
collision_.p.2	point	Left Top corner of the second element checked
collision_.hitbox1	1 bytes	Id of the hitbox of the first element checked
collision_.hitbox2	1 bytes	Id of the hitbox of the second element checked
collision_.p_RD.1	point	Right Down corner of the first element checked
collision_.p_RD.2	point	Right Down corner of the second element checked

Pseudo code

char collision(
  char collision_.p.1,
  char collision_.p.2,
  char collision_.hitbox1,
  char collision_.hitbox2){
    // INIT
    collision_.p_RD.1.x = collision_.p.1.x + hitboxs_width[collision_.hitbox1];
    collision_.p_RD.1.y = collision_.p.1.y + hitboxs_height[collision_.hitbox1];
    collision_.p_RD.2.x = collision_.p.2.x + hitboxs_width[collision_.hitbox2];
    collision_.p_RD.2.y = collision_.p.2.y + hitboxs_height[collision_.hitbox2];
    // COMPARE
    if (collision_.p.1.x > collision_.p_RD.2.x) // 1 is to the left off 2
      return 0;
    if (collision_.p.2.x > collision_.p_RD.1.x) // 2 is to the left off 1
      return 0;
    if (collision_.p.2.y > collision_.p_RD.1.y) // 1 is upper than 2
      return 0;
    if (collision_.p.1.y > collision_.p_RD.2.y) // 2 is upper than 1
      return 0;
    return 1;
}

• INIT generates the right/down points of the two objects from there hitboxs and left/up points.

• COMPARE checks if left of the first element is to the right of the right of the second element. If yes, there are no collision, 1 is to the left of 2. Then we check if 2 is to the left of 1, if 1 is upper than 2, and if 2 is upper than 1. After that, we know the two objects collide.

Notes

This function is critical. It has to be optimized.

TODO

• Optimisation, wait until the variables are needed before initialisating them.

• Find a way to tel if one element is already loaded.

• Can we efficiently detect the side of the collision?

• Does using a point instead of a hitbox for ine element improve the performance?