Can't shoot to the right direction

[ruimika90]

I have a object that is always rotating with a cannon. I want to shoot a bullet, but when I do, it goes always to the right direction instead of the cannon direction. I tried to offset the bullet. What I am doing wrong?

local function go(event)
    display.remove(logo)
    display.remove(begin)
    local planet = display.newImage(“images/earth.png”)
    planet.x = centerX
    planet.y = centerY
    – Esta função faz a terra rodar e aumento a sua rotação por cada 10 segundos
    local function animate()
        planet.rotation = planet.rotation + 2
        earthRotation = timer.performWithDelay( 10000, animate)
    end
    Runtime:addEventListener(“enterFrame”,animate);
    planet:scale(4, 4)
    transition.to( planet, { time = 200, xScale = 1, yScale = 1, onComplete = animate} )
    startGame()
    timerGame()
    timeCount()
    local function firebullet()
        local bullet = display.newCircle( planet.x, planet.y, 2 )
        physics.addBody( bullet, { density=3.0, friction=0.5, bounce=0.05 } )
        bullet.isBullet = true
        function getBulletOffset(planet, offsetAngle, offsetDist )
            local offset = math2d.angle2Vector( planet.rotation + offsetAngle, true )
            offset = math2d.scale( offset, offsetDist )
        return planet.x + offset.x, planet.y + offset.y
        end
        local bulletStartX, bulletStartY = getBulletOffset( planet, 90, 15 )
        bullet.angularVelocity = 50
        bullet:applyForce( 100, 0, bullet.x, bullet.y )
        local bulletStartX, bulletStartY = getBulletOffset( planet, 90, 15 )
        
    end
    bg:addEventListener ( “tap”, firebullet)
    end
    begin:addEventListener ( “tap”, go)

[bjsorrentino]

Hi @ruimika90,

The reason your bullet is always going to the right is in how you’ve typed this line:

[lua]

bullet:applyForce( 100, 0, bullet.x, bullet.y )

[/lua]

That is basically applying a force in the “x” direction of 100, every time, so the bullet just goes right. Instead of using “100, 0” for the first 2 arguments, you’ll need to get the proper vector values from the “math2d” library, and tell Corona to apply the proper force in both the “x” and “y” directions.

Hope this helps,

Brent

[ruimika90]

Hi @BrentSorrentino,

Is there any way to get the direction to where the cannon (while rotating) is pointing when the user tap the screen, and then use a vector to fire the bullet in that direction?

Thx for the help,

Rui

[frasderp]

Hi ruimika90. You’re missing a few essentials, as BrentSorrentino said, you are essentially telling it to apply ‘100’ force in the x direction, and no force in the y.

I suggest having a read about touch and tap events, and how you can pick up the coordinates of a touch.

An example of what you’ll need to make it work below -

[lua]

local function firebullet(event)

–Find difference between planet to the touch coordinates

local deltax = planet.x - event.x

local deltay = planet.y - event.y

–Find angle between planet and touch (in radians)

local bulletangle = math.atan2(deltay, deltax)

–Apply a force of ‘100’ at the angle between planet and touch coordinates

local xforce = (math.cos(angle))*100

local yforce = (math.sin(angle))*100

– Instead of this - bullet:applyForce( 100, 0, bullet.x, bullet.y )

bullet:applyForce( xforce, yforce, bullet.x, bullet.y )

[/lua]

I hope this helps, this is my first attempt at helping somebody with Corona

[ruimika90]

Hi @frasderp,

Thx for the code and for the help, but the code is giving an error “bad argument 1# to cos(number expected, got nil)”. Any idea of what is causing this error and how to solve it?

Thx Again,

Rui

[frasderp]

@ruimika90

Hi @frasderp,

Thx for the code and for the help, but the code is giving an error “bad argument 1# to cos(number expected, got nil)”. Any idea of what is causing this error and how to solve it?

Thx Again,

Rui

Apologies, I used the wrong reference to angle - 

Replace this section with the following.

[lua]

local xforce = (math.cos(bulletangle))*100

local yforce = (math.sin(bulletangle))*100

[/lua]

[ruimika90]

Ok, the error is gone, but what the planet is doing now, is shooting to the opposite direction of where you tap. For example, if I tap in the left of the planet, it will shoot to the right. What I really want to try, is, when we tap, it will shoot to the direction where the cannon is pointing while rotating.

Again, thx for all the help.

[frasderp]

Change this part

[lua]

–change this

local deltax = planet.x - event.x
local deltay = planet.y - event.y

–to this

local deltax = event.x - planet.x
local deltay = event.y - planet.y

[/lua]

[bjsorrentino]

Hi @ruimika90,

The reason your bullet is always going to the right is in how you’ve typed this line:

[lua]

bullet:applyForce( 100, 0, bullet.x, bullet.y )

[/lua]

That is basically applying a force in the “x” direction of 100, every time, so the bullet just goes right. Instead of using “100, 0” for the first 2 arguments, you’ll need to get the proper vector values from the “math2d” library, and tell Corona to apply the proper force in both the “x” and “y” directions.

Hope this helps,

Brent

[ruimika90]

Hi @BrentSorrentino,

Is there any way to get the direction to where the cannon (while rotating) is pointing when the user tap the screen, and then use a vector to fire the bullet in that direction?

Thx for the help,

Rui

[frasderp]

Hi ruimika90. You’re missing a few essentials, as BrentSorrentino said, you are essentially telling it to apply ‘100’ force in the x direction, and no force in the y.

I suggest having a read about touch and tap events, and how you can pick up the coordinates of a touch.

An example of what you’ll need to make it work below -

[lua]

local function firebullet(event)

–Find difference between planet to the touch coordinates

local deltax = planet.x - event.x

local deltay = planet.y - event.y

–Find angle between planet and touch (in radians)

local bulletangle = math.atan2(deltay, deltax)

–Apply a force of ‘100’ at the angle between planet and touch coordinates

local xforce = (math.cos(angle))*100

local yforce = (math.sin(angle))*100

– Instead of this - bullet:applyForce( 100, 0, bullet.x, bullet.y )

bullet:applyForce( xforce, yforce, bullet.x, bullet.y )

[/lua]

I hope this helps, this is my first attempt at helping somebody with Corona

[ruimika90]

Hi @frasderp,

Thx for the code and for the help, but the code is giving an error “bad argument 1# to cos(number expected, got nil)”. Any idea of what is causing this error and how to solve it?

Thx Again,

Rui

[frasderp]

@ruimika90

Hi @frasderp,

Thx for the code and for the help, but the code is giving an error “bad argument 1# to cos(number expected, got nil)”. Any idea of what is causing this error and how to solve it?

Thx Again,

Rui

Apologies, I used the wrong reference to angle - 

Replace this section with the following.

[lua]

local xforce = (math.cos(bulletangle))*100

local yforce = (math.sin(bulletangle))*100

[/lua]

[ruimika90]

Ok, the error is gone, but what the planet is doing now, is shooting to the opposite direction of where you tap. For example, if I tap in the left of the planet, it will shoot to the right. What I really want to try, is, when we tap, it will shoot to the direction where the cannon is pointing while rotating.

Again, thx for all the help.

[frasderp]

Change this part

[lua]

–change this

local deltax = planet.x - event.x
local deltay = planet.y - event.y

–to this

local deltax = event.x - planet.x
local deltay = event.y - planet.y

[/lua]