I am starting a new thread to address a specific question. I searched the forums and didn’t find anything. If I missed it, let me know, and I will follow that lead. But, here is my situation:
I am working on a small project, and would like to have a sprite move in the direction of where I am touching on the screen. Below is my code (that does not work). I made comments what I think the code should be doing.
-- #Main
--displayMode(FULLSCREEN)
supportedOrientations(CurrentOrientation)
-- Use this function to perform your initial setup
function setup()
m = Mine()
end
-- This function gets called once every frame
function draw()
-- This sets a dark background color
background(142, 88, 38, 255)
mineTouch()
-- Do your drawing here
m:draw()
end
function mineTouch()
if CurrentTouch.state == BEGAN and MOVING then
if CurrentTouch.x < WIDTH then -- if touching inside the screen
if CurrentTouch.y < HEIGHT then
-- move the sprite position towards the current touch
m.pos = m.pos + vec2(CurrentTouch.x,CurrentTouch.y)
end
end
end
if CurrentTouch.state == ENDED then
-- stop the sprite at its location
m.pos = m.pos
end
end
-- #Mine
Mine = class()
function Mine:init(x)
-- you can accept and set parameters here
self.pos = vec2(WIDTH/2, HEIGHT/2)
end
function Mine:draw()
-- Codea does not automatically call this method
sprite("Tyrian Remastered:Mine Spiked Huge",self.pos.x,self.pos.y)
end
function Mine:touched(touch)
-- Codea does not automatically call this method
end
I don’t want the sprite to “jump” to the CurrentTouch. I want it to be drawn every frame moving towards the CurrentTouch. Thanks.
This isn’t exactly what you had in mind, but I think this example might help.
`
function setup()
x = 100
y = 100
end
function draw()
background(40, 40, 50)
strokeWidth(5)
ellipse(CurrentTouch.x, CurrentTouch.y, 10, 10)
sprite("Planet Cute:Character Boy", x, y)
local deltaX = 0
local deltaY = 0
if x < CurrentTouch.x then
deltaX = 1
else
deltaX = -1
end
if y < CurrentTouch.y then
deltaY = 1
else
deltaY = -1
end
x = x + deltaX
y = y + deltaY
end
`
To make the sprite stop animating you could add something like this:
-- #Main
displayMode(FULLSCREEN)
supportedOrientations(CurrentOrientation)
-- Use this function to perform your initial setup
function setup()
m = Mine()
mineStep = 1
mineX = WIDTH/2
mineY = HEIGHT/2
targetX = mineX
targetY = mineY
end
-- This function gets called once every frame
function draw()
-- This sets a dark background color
background(142, 88, 38, 255)
mineTouch()
-- Do your drawing here
if targetX > mineX then mineX = mineX + mineStep end
if targetX < mineX then mineX = mineX - mineStep end
if targetY > mineY then mineY = mineY + mineStep end
if targetY < mineY then mineY = mineY - mineStep end
Mine:draw(mineX, mineY)
end
function mineTouch()
if CurrentTouch.state == BEGAN or CurrentTouch.state == MOVING then
targetX = CurrentTouch.x
targetY = CurrentTouch.y
end
if CurrentTouch.state == ENDED then
-- stop the sprite at its location
targetX = mineX
targetY = mineY
end
end
For the main.lua, And here is the Mine.lua.
-- #Mine
Mine = class()
function Mine:init(x)
-- you can accept and set parameters here
self.pos = vec2(WIDTH/2, HEIGHT/2)
end
function Mine:draw(x,y)
-- Codea does not automatically call this method
sprite("Tyrian Remastered:Mine Spiked Huge",x,y)
end
function Mine:touched(touch)
-- Codea does not automatically call this method
end
function setup()
m = Mine()
end
function draw()
background(142, 88, 38, 255)
m:draw()
end
function touched(t)
m:touched(t)
end
Mine = class()
function Mine:init(x)
self.pos = vec2(WIDTH/2, HEIGHT/2)
self.velocity = vec2(0,0)
self.speed = 4
end
function Mine:draw()
self.pos = self.pos + self.velocity
sprite("Tyrian Remastered:Mine Spiked Huge",self.pos.x,self.pos.y)
end
function Mine:touched(touch)
if touch.state == ENDED then
self.velocity = vec2(0,0)
else
self.velocity = vec2(touch.x,touch.y) - self.pos
self.velocity = self.velocity / self.velocity:len() * self.speed
end
end
@Tao thanks. I was able to follow that example and get my sprite to move on the x-axis…
@ruilov I put in your code. That is what I was going for. Could you explain some things for me? Is velocity a built in code thing? What is happening in ~~~ self.velocity = self.velocity / self.velocity:len() * self.speed ~~~ also, I noticed when the sprite reached the place of touch, it would continue moving, and then come back to the touch point. But it never just stopped at the touch point. Do you know what causes that and how to make it stop at the touch point? Lastly, what is t in m:touched(t)?
“Velocity” is not a built in thing - Ruilov defines it as a property of the “Mine” class so that every instance (object) of this class has its own velocity.
In Ruilov’s code, the sprite always has a velocity towards the touch point and this velocity always has the same magnitude. This leads to the overshoot: as the sprite gets really close to the touch point, it is still moving with the same speed and so goes past. It might stop if it ever landed exactly on the touch point, but Ruilov’s code contains a little problem if that ever happened because then it would be trying to divide by the length of a zero vector - not generally a good thing. So what would probably happen is that the code would stop running due to an error.
There are a variety of different ways to fix that. I prefer to have the object experience a force towards the touch point and then compute the acceleration and velocity from that - this means that if you change the touch point then it doesn’t instantly swing round and start moving towards it but rather undergoes a more realistic movement.
Another way is simply to take out the division by the length of the velocity (/ self.velocity:len()). Probably would want to adjust the speed a bit to tune the behaviour on that. Then it will get slower as it approaches the touch point.
re m:touched(t): instead of using CurrentTouch you can implement a special function called “touched” that gets called whenever a touch event happens (a touch starts or moves or ends). This is most useful if you want to handle multi touches (check out the multi touch example), but I also find cleaner than using CurrentTouch so it’s what I tend to use. Codea calls my touched(t) function and inside it I call m:touched.
The overshooting problem only happens if you keep your finger still on the screen, because then touch events stop being generated and self.velocity stays the same. If you leave your finger there long enough, the object will go off screen.
Perhaps better to keep track of the “target” where the object is trying to get to. Something like this: (I’m away from the ipad so this might not work):
function setup()
m = Mine()
end
function draw()
background(142, 88, 38, 255)
m:draw()
end
function touched(t)
m:touched(t)
end
Mine = class()
function Mine:init(x)
self.pos = vec2(WIDTH/2, HEIGHT/2)
self.target= self.pos
self.speed = 4
end
function Mine:draw()
local move = self.target - self.pos
if move:len() > self.speed then
move = move / move:len() * self.speed
end
self.pos = self.pos + move
sprite("Tyrian Remastered:Mine Spiked Huge",self.pos.x,self.pos.y)
end
function Mine:touched(touch)
self.target = vec2(touch.x,touch.y)
end
Thanks Bri_G and ruilov. Both worked. The sprite moved towards the touch. They both are slightly different. Bri_G’s code stops the sprite as soon as the touch ends. ruilov’s sprite continues to move to the target touch even after the touch has ended. I like both of them, and will keep these as references. Again, thanks. Now on to collisions.
One more request to ruilov (if you don’t mind). Could you explain WHY you used the math formula (I understand where the values are coming from) in the following:
Is this an algebra formula like rate * time = distance?
move is a vector, which describes a direction and a magnitude (length). Dividing it by it’s length (an operation called “normalizing”) gives you what’s known as a unit vector, which describes a direction with a length of 1 (in other words, it’s a pure direction). Multiplying the unit vector by your speed will cause it’s length to be equal to your speed, so if you were to add that to a point, that point would move in the direction the vector represents by the length of the vector.
