game maker code

jump_grav = -9;
if !place_meeting(x,y+1,block_items) // if I am in the air
{
    grav = .5; // set the gravity to .5
    vspd += grav; // add .5 to our vspd once every step
}
else // else if I am on the ground
{
    grav = 0; // set the gravity to 0
    vspd = 0; // set vspd to 0 to stop moving
    if keyboard_check_pressed(vk_up) // since I am on the ground, I can handle jumping here, so check if I pressed up
    {
        vspd = jump_grav; // set the vspd to a negative number, which will make us jump
    }
}
if keyboard_check_released(vk_up) // if I released the up button while in the in air
{
    vspd *= .5; // divide our vspd by 2, creating a smooth type of variable jumping
}
if vspd > 8 // I don't want to fall too fast, so lets limit our vspd
{
    vspd = 8; // note that if you want to be able to fall fast, you can remove this without affecting the code (but I wouldn't)
}
repeat(abs(vspd)) // I want to check for a collision every pixel, so I use a repeat() function to check every pixel while falling
{
    if !place_meeting(x,y+sign(vspd),block_items) // vspd can be negative or positive, so I check 1 pixel above or below, depending on which direction I am going
    {
        y += sign(vspd); // add to our y value 1 pixel at a time, letting use check for a collision every pixel
    }
    else // else if I hit a block
    {
        vspd = 0; // stop moving vertically
    }
}
hspd = (keyboard_check(vk_right)-keyboard_check(vk_left))*4; // a nice little trick that will set our hspd to +4 or -4 depending what button I am holding
repeat(abs(hspd)) // same as the vspd, I want to check for a collision at every pixel I move
{
    if !place_meeting(x+sign(hspd),y,block_items) // if there is no block to our left or right
    {
        x += sign(hspd); // add to our x value depending on which way I am going
    } else if place_meeting(x+sign(hspd),y,bi_allow_colide){
        x += sign(hspd);
        hspd = 0;
    }
    if (hspd==-4)
    {
        lastwalk = 1;
    }
    if (hspd==4)
    {
        lastwalk = 2;
    }
}