hey guys, can you please explain the hit function in my code. I used a tutorial for it but i want to understand it.

x = 63
y = 35
dx = 0
dy = 0
grid_x = 0
grid_y = 0
map_tile = 0
flag_tile = 0
function _update()
dx = 0
dy = 0
grid_x = flr(x/8)
grid_y = flr(y/8)
flag_tile = fget(mget(grid_x,grid_y))
if btn(⬅️) then dx = -1 end
if btn(➡️) then dx = 1 end
if btn(⬆️) then dy = -1 end
if btn(⬇️) then dy = 1 end
if hit(x+dx,y,7,7) then
dx = 0
end
if hit(x,y+dy,7,7) then
dy = 0
end
x += dx
y += dy
end
function _draw()
cls()
map(0,0,0,0,16,16)
spr(2,x,y)
end
function hit(x,y,w,h)
collide = false
for i=x,x+w,w do
if fget(mget(i/8,y/8))>0 or
fget(mget(i/8,(y+h)/8))>0 then
collide = true
end
end
return collide
end

It's an interesting implementation, hit() takes a rectangle at upper left corner x,y with width w and height h, it loops through each x-coord from x to x+w and checks if the pixel at that x coord and the y coord (top) of the rectangle, or the pixel at that x coord and the y coord +h (which is actually one pixel below the bottom edge of the rect and thus likely why 7 is being passed in instead of 8) hits a tile with any flags set (not just a specific flag but any).

So, it's really only checking the top and bottom edges, and each and every pixel of those edges. Which will work as long as the rect is no taller than a map tile (8px) since the vertical edges aren't checked, but it's excessive for the horizontal edges as only 1 check is needed per 8px as well. It would be more efficient (for rects of 8px or less in width and height) to check the four corners only.

Also, bear in mind that as x+dx and y+dy are passed into the function, this will stop an object from completing a move into a solid tile but may do so at a few pixels away if the object is moving faster than 1px per frame on a given axis.