Pygame：将对象移向位置

Question

Is there an algorithm to change a set of coordinates to make it move towards another set of coordinates?

Like, if I have ax,ay=(20,30) and bx,by=(40,60)

I can't seem to wrap my head around this. How can I change ax and ay (over time) to equal bx and by ? (Preferably an algorithm achievable in python.)

Answer 1

It's pretty easy if you think about it. To create the illusion of movement you need to create an animation - that is, moving the object step by step .

The object needs to move 20 pixels horizontally ( bx - ax = 20 ) and 30 pixels vertically ( by - ay = 60 ). Now, you need to define how many steps the object will spend moving. That essentially depends on the framerate of your game, if you want the animation to last 1 second and your game runs at 25fps, the animation will take 25 steps. If your game does not have a fixed framerate but something else, you'll need to compute the amount of movement for each iteration of the game loop depending on the elapsed time from the last frame.

Let's suppose we're runing at a fixed speed of 25fps. In that case, you'd need to do something like:

dx, dy = (bx - ax, by - ay)
stepx, stepy = (dx / 25., dy / 25.)

Now, stepx and stepy have the amount of movement needed in each step. What you need to do is add that in each iteration of the game loop:

# In each iteration:
object.set_position(object.x + stepx, object.y + stepy)

Answer 2

steps_number = max( abs(bx-ax), abs(by-ay) )

stepx = float(bx-ax)/steps_number
stepy = float(by-ay)/steps_number

for i in range(steps_number+1):
    print int(ax + stepx*i), int(ay + stepy*i)

result:

20 30
20 31
21 32
22 33
22 34
23 35
24 36
24 37
25 38
26 39
26 40
27 41
28 42
28 43
29 44
30 45
30 46
31 47
32 48
32 49
33 50
34 51
34 52
35 53
36 54
36 55
37 56
38 57
38 58
39 59
40 60

Answer 3

As you are using pygame, then you can use vectors to move your object on the screen.

import pygame as pg

vec = pg.math.Vector2
a = vec(20, 30)
b = vec(40, 60)
a += b

Put it in your loop and add speed to slow it down. Your object will move toward the "b" point and will pass it when it reachs that point.