GYROSCOPE

victor_cappa · August 2013

Hello everybody!
I was searching in the forum for a answer, but I didn't find it, so...
I'm trying to make a character move to one side of screen to the other using the gyroscope, but I'm not able to find the right code to do this.
I'm newbie, sorry about the stupid question

Thank you!

ar2rsawseen · August 2013

@victor_cappa I could not say it should be done with gyroscope, better with accelerometer. Check out the Accelereometer example in the Hardware section of examples inside Gideros Studio

victor_cappa · August 2013

Oh thank you!
I'm trying to make a doodle jump kind of game (learning purposes).

ar2rsawseen · August 2013

Then this example should be exactly what you need, just adjust some ratios to your feel and you can use only x axis.
And here is also a Doodle Jump template:
http://giderosmobile.com/forum/discussion/473/let039s-jump-d/p1

victor_cappa · August 2013

Nice! I saw that example, but it uses mouse_down and mouse_up events. I'm trying to replace that with the accelerometer.
You were really helpful, thank you again!

victor_cappa · August 2013

Hi ar2rsawseen! I erase the 'onMouseDown' event and I put the code below, but I'm getting this error:

"character.lua:50: attempt to index global 'self' (a nil value)
stack traceback:
character.lua:50: in main chunk"

here is the whole code:

require "box2d"
b2World = b2.World.new(0, 15, true);

GCchar = gideros.class(Bitmap)

function GCchar:init()
self:setAnchorPoint(0.5, 0.5);
self.body = b2World:createBody{type = b2.DYNAMIC_BODY,
};
self:setPosition(160, 492);
self.body:setPosition(self:getPosition());
local blockShape = b2.PolygonShape.new();
blockShape:setAsBox(self:getWidth()*0.5, self:getHeight()*0.5);
self.body:createFixture{shape = blockShape,
friction = 0,
restitution = 0,
density = 5,
isSensor = false
};
self:addEventListener(Event.ENTER_FRAME, self.onEnterFrame, self);
b2World:addEventListener(Event.BEGIN_CONTACT, self.onBeginCollision, self);
self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self);
self.body:setLinearVelocity(0, -15);
end

function GCchar:onEnterFrame()
b2World:step(1/60, 8, 3);
self:getParent():addChild(self);
self:setPosition(self.body:getPosition());
local selfX, selfY = self:getParent():localToGlobal(self:getPosition());
if selfY < 250 then
self:getParent():setY(250 -self:getY());
end
if selfX < 0 then -- para o char poder ir da esquerda para a direita e vice versa
local bodyX, bodyY = self.body:getPosition();
self.body:setPosition(320, bodyY);
elseif selfX > 320 then
local bodyX, bodyY = self.body:getPosition();
self.body:setPosition(0, bodyY);
end
end

------------------------include accelerometer------------------------
require "accelerometer"
accelerometer:start()
self.filter = 0.5
self.fx = 0
self.gravityScale = 10
-- get accelerometer values
local x, y = accelerometer:getAcceleration()
-- apply IIR filter
self.fx = x * self.filter + self.x * (1 - self.filter)
self.world:setGravity(self.fx*self.gravityScale)

function GCchar:onEnterFrame(event)
local xSpeed, ySpeed = self.body:getLinearVelocity();
if event.x < 160 then
self.body:setLinearVelocity(-8, ySpeed);
else
self.body:setLinearVelocity(8, ySpeed);
end
event:stopPropagation();
end
function GCchar:onMouseUp(event)
local xSpeed, ySpeed = self.body:getLinearVelocity();
self.body:setLinearVelocity(0, ySpeed);
event:stopPropagation();
end

function GCchar:onBeginCollision(event) -- colisão
local bodyA, bodyB = event.fixtureA:getBody(), event.fixtureB:getBody();
if bodyA == self.body or bodyB == self.body then
local xSpeed, ySpeed = self.body:getLinearVelocity();
if ySpeed > 0 then
self.body:setLinearVelocity(xSpeed, -15);
end
end
end

ar2rsawseen · August 2013

@victor_cappa you just need to include your accelerometer code into function GCchar:onEnterFrame() and not outside of it

victor_cappa · August 2013

I can't figure out what I'm doing wrong

... Now I'm getting this error

character.lua:52: attempt to perform arithmetic on field 'x' (a nil value)
stack traceback:
character.lua:52: in function

I include de acceleromater code into function GCchar:onEnterFrame()

require "box2d"
b2World = b2.World.new(0, 15, true);

GCchar = gideros.class(Bitmap)

function GCchar:init()
self:setAnchorPoint(0.5, 0.5);
self.body = b2World:createBody{type = b2.DYNAMIC_BODY,
};
self:setPosition(160, 492);
self.body:setPosition(self:getPosition());
local blockShape = b2.PolygonShape.new();
blockShape:setAsBox(self:getWidth()*0.5, self:getHeight()*0.5);
self.body:createFixture{shape = blockShape,
friction = 0,
restitution = 0,
density = 10,
isSensor = false
};
self:addEventListener(Event.ENTER_FRAME, self.onEnterFrame, self);
b2World:addEventListener(Event.BEGIN_CONTACT, self.onBeginCollision, self);
self:addEventListener(Event.MOUSE_DOWN, self.onMouseDown, self);
self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self);
self.body:setLinearVelocity(0, -13);
end

function GCchar:onEnterFrame()
b2World:step(1/60, 8, 3);
self:getParent():addChild(self);
self:setPosition(self.body:getPosition());
local selfX, selfY = self:getParent():localToGlobal(self:getPosition());
if selfY < 240 then
self:getParent():setY(240-self:getY());
end
if selfX < 0 then
local bodyX, bodyY = self.body:getPosition();
self.body:setPosition(320, bodyY);
elseif selfX > 320 then
local bodyX, bodyY = self.body:getPosition();
self.body:setPosition(0, bodyY);
end
------------------------include accelerometer------------------------
require "accelerometer"
accelerometer:start()
self.filter = 0.5
self.fx = 0
self.gravityScale = 10
-- get accelerometer values
local x, y = accelerometer:getAcceleration()
-- apply IIR filter
self.fx = x * self.filter + self.x * (1 - self.filter)
self.world:setGravity(self.fx*self.gravityScale)
end

function GCchar:onMouseDown(event)
local xSpeed, ySpeed = self.body:getLinearVelocity();
if event.x < 160 then
self.body:setLinearVelocity(-4, ySpeed);
else
self.body:setLinearVelocity(4, ySpeed);
end
event:stopPropagation();

end

function GCchar:onMouseUp(event)
local xSpeed, ySpeed = self.body:getLinearVelocity();
self.body:setLinearVelocity(0, ySpeed);
event:stopPropagation();
end

function GCchar:onBeginCollision(event)
local bodyA, bodyB = event.fixtureA:getBody(), event.fixtureB:getBody();
if bodyA == self.body or bodyB == self.body then
local xSpeed, ySpeed = self.body:getLinearVelocity();
if ySpeed > 0 then
self.body:setLinearVelocity(xSpeed, -13);
end
end
end

I guess I need to study more theory before study 'real codes'...

ar2rsawseen · August 2013

the line

self.fx = x * self.filter + self.x * (1 - self.filter)

was supposed to be

self.fx = x * self.filter + self.fx * (1 - self.filter)

change self.x to self.fx

victor_cappa · August 2013

I don't know how i missed that :P
But now it says that 'character.lua:52: attempt to index field 'world' (a nil value)
stack traceback:
character.lua:52: in function '

about this line of the code

self.fx = x * self.filter + self.fx * (1 - self.filter)
self.world:setGravity(self.fx*self.gravityScale)

ar2rsawseen · August 2013

well instead self.world you need to use the instance you've created: b2World

victor_cappa · August 2013

It worked!
Now I'm trying to figure out how to only use x axis... When I take the

self.fy*self.gravityScale

from here

b2World:setGravity(self.fx*self.gravityScale, - self.fy*self.gravityScale)

I get an error "character.lua:45: bad argument #2 to 'setGravity' (number expected, got no value)"

But it was really helpful to my learnig process

ar2rsawseen · August 2013

For the y vector of gravity you just use same constant you used when creating the world:

b2World:setGravity(self.fx*self.gravityScale, 15)

but setting gravity is only one way, you could also experiment with applying impulses or setting linear velocity. Just make sure it won't go off your screen

victor_cappa · August 2013

I'm always impressed about the patience that everybody in this forum have with newbies... I can't be more thankful ar2rsawseen!

ar2rsawseen · August 2013

Well, we've all been there

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