Sticky-sticky

main.lua

local pivot = {
   x = 200,
   y = 200,
   w = 100,
   h = 150,
}

local rect = {
   x = 0,
   y = 0,
   w = 150,
   h = 100,
}

function draw_rect(rect)
   love.graphics.rectangle("line", rect.x, rect.y, rect.w, rect.h);
end

function rect_overlap(rect1, rect2)
   return rect1.x + rect1.w >= rect2.x
      and rect2.x + rect2.w >= rect1.x
      and rect2.y + rect2.h >= rect1.y
      and rect1.y + rect1.h >= rect2.y
end

function rect_center(rect)
   return {
      x = rect.x + rect.w * 0.5,
      y = rect.y + rect.h * 0.5,
   }
end

function sign(x)
   return x / math.abs(x)
end

function rect_impulse(r1, r2)
   local c1 = rect_center(r1)
   local c2 = rect_center(r2)
   local d = math.min(c1.x, c2.x) + math.abs(c1.x - c2.x) * 0.5

   if c1.x < c2.x then
      return
         {
            x = d - r1.w,
            y = r1.y,
            w = r1.w,
            h = r1.h,
         },
         {
            x = d,
            y = r2.y,
            w = r2.w,
            h = r2.h,
         }
   else
      return
         {
            x = d,
            y = r1.y,
            w = r1.w,
            h = r1.h,
         },
         {
            x = d - r2.w,
            y = r2.y,
            w = r2.w,
            h = r2.h,
         }
   end
end

function rect_snap(p, r)
   local pc = rect_center(p)
   local rc = rect_center(r)

   local x = pc.x + sign(rc.x - pc.x) * (p.w + r.w) * 0.5 - r.w * 0.5
   local y = pc.y + sign(rc.y - pc.y) * (p.h + r.h) * 0.5 - r.h * 0.5

   if math.abs(x - rc.x) < math.abs(y - rc.y) then
      return {
         x = x,
         y = r.y,
         w = r.w,
         h = r.h
      }
   else
      return {
         x = r.x,
         y = y,
         w = r.w,
         h = r.h
      }
   end
end

function love.draw()
   love.graphics.setColor(255, 255, 255, 255)
   draw_rect(pivot)
   draw_rect(rect)
end

function love.update(dt)
   rect.x = love.mouse.getX() - rect.w * 0.5
   rect.y = love.mouse.getY() - rect.h * 0.5

   if rect_overlap(pivot, rect) then
      pivot, rect = rect_impulse(pivot, rect)
   end
end