Super Basic Question

joethemojo · February 2014

I'm very new to Gideros and I have looked around for this answer but I'm getting a little frustrated.

I'm starting off very basic.

Id like to move a sprite with the arrow keys on the keyboard.
and after you release to key the sprite still moves a little in that direction.

I have no idea how to do this.
Ive looked in the reference and I think I somehow merge these 2 codes?

function onMouseDown(event)
print(event.x, event.y) <--- but a translate function?
end
mysprite:addEventListener(Event.MOUSE_DOWN, onMouseDown)

with

stage:addEventListener(Event.KEY_DOWN, function(event)
if event.keyCode == KeyCode.BACK then
application:exit() <----- with translate function?
end
end)

Then I think another event for when I let go of the key?

If anyone could help me Id greatly appreciate this.

Joe

eezing · February 2014

Here's an example of how act upon key up/down. As far as moving a sprite... that would be separate functionality.

 
-- The sprite that will listen for key up/down events
 
local sprite = Sprite.new()
stage:addChild(sprite)
 
 
 
-- Assign Up arrow as our move key
 
local moveKey = KeyCode.UP
 
 
 
 
-- Our function when key is pressed
 
local function move()
 
	print("begin moving")
end
 
-- Our funcion when key is released
 
local function stop()
 
	print("begin stop moving")
end
 
 
 
 
-- Our listener function for when key is Down
 
local function onKeyDown(event)
 
	if event.keyCode == moveKey then
 
		move()
 
	end
end
 
-- Our listener function for when key goes Up
 
local function onKeyUp(event)
 
	if event.keyCode == moveKey then
 
		stop()
 
	end
end
 
 
 
-- Our event listeners to start the actions
 
sprite:addEventListener(Event.KEY_DOWN, onKeyDown, event)
sprite:addEventListener(Event.KEY_UP, onKeyUp, event)

joethemojo · February 2014

Thank you!!!

eezing · February 2014

For moving sprites...

There's probably a bunch of examples in these forums... but there are basically two ways.

The first way is to use box2d if you require sprites to interact and collide with each other. Box2d at first can be a bit overwhelming, but extremely valuable once you get the hang of it.

The second is something like this (using my example above):

-- The sprite that will listen for key up/down events
 
local sprite = Sprite.new()
stage:addChild(sprite)
 
 
-- Define attributes of move action for sprite
 
local fps = 60
local speed = 200
local drag = 0.05
local stopAtSpeed = 5
 
 
-- The moving function that will run on every frame
 
local sx = stopAtSpeed * (1 / fps)
local dx, dsx, x = 0, 0, 0
 
local function moving()
 
	-- get next amount to move
	dx = dx * (1 - dsx)
 
	-- new position = last position + next amount to move
	x = x + dx
	sprite:setX(x)
 
	-- if next amount to move is less than this, kill listener
	if math.abs(dx) < sx then
 
		if sprite:hasEventListener(Event.ENTER_FRAME) then
			sprite:removeEventListener(Event.ENTER_FRAME, moving)
		end
	end
 
	print(x, dx)
end
 
--------------------------------------------------
 
-- Assign Up arrow as our move key
 
local moveKey = KeyCode.UP
 
 
 
-- Our function when key is pressed
 
local function move()
 
	-- No drag when moving
	dsx = 0
 
	-- Set our amount to move to full
	dx = speed * (1 / fps)
 
	-- Get starting position
	x = sprite:getX()
 
	-- Start listening at every frame
	if not sprite:hasEventListener(Event.ENTER_FRAME) then
		sprite:addEventListener(Event.ENTER_FRAME, moving)
	end
end
 
-- Our funcion when key is released
 
local function stop()
 
	-- Apply drag
	dsx = drag
end
 
 
 
 
-- Our listener function for when key is Down
 
local function onKeyDown(event)
 
	if event.keyCode == moveKey then
 
		move()
 
	end
end
 
-- Our listener function for when key goes Up
 
local function onKeyUp(event)
 
	if event.keyCode == moveKey then
 
		stop()
 
	end
end
 
 
 
-- Our event listeners to start the actions
 
sprite:addEventListener(Event.KEY_DOWN, onKeyDown, event)
sprite:addEventListener(Event.KEY_UP, onKeyUp, event)

OZApps · February 2014

@joethemojo,
you are aware that not all mobile devices would have and respond to the arrow keys.

john26 · February 2014

A KEY_DOWN event only fires when the user first presses the key down. When the user releases the key, a KEY_UP event occurs. But in between there are no events. It's important to realize the system will not constantly send you a series of KEY_DOWN events. So you need a boolean variable eg keypressed which you set to true when you get KEY_DOWN and false when you get KEY_UP. Then, you use an ENTER_FRAME listener to update the sprite position, eg

if keypressed then sprite:setX(sprite:getX()+1) end.

Same deal for MOUSE_DOWN, MOUSE_UP.

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