Having trouble with a cannon firing...

Games
#1

Hi. I’m eleven years old and a novice at Corona. This may be relevant to the current topic (having balls shoot in the correct direction).

I created a cannonBall and a cannon and made them a single group and put them in the same place. I created a working method of rotating the cannon via touch:

local function rotateTo (event)
local deg = math.atan2( event.y - cannonGroup.y, event.x - cannonGroup.x )
cannonGroup.rotation = math.deg(deg)
end

However, after creating a shootBall function (using the code given kindly by indiegamepod) and applying it and the rotateTo function to a turnAndShoot function:

local function turnAndShoot (event)
if ( event.phase == “began” ) then
timer.performWithDelay( 1, rotateTo, 0 )
end
if ( event.phase == “ended” ) then
timer.performWithDelay( 1, shootBall )
end
end

the cannon will rotate with the touch perfectly, but the shootBall function will not call. Why is this? [import]uid: 82408 topic_id: 15607 reply_id: 315607[/import]

#2

you need to use the phase “moved” as well to get events from when the touch is moved [import]uid: 5354 topic_id: 15607 reply_id: 57642[/import]

#3

it looks like you have it set to shoot the ball when the touch ends now [import]uid: 5354 topic_id: 15607 reply_id: 57649[/import]

#4

I changed the code again:

[code]
local function turnAndFire (event)
local deg = math.atan2( event.y - cannonGroup.y, event.x - cannonGroup.x )
cannonGroup.rotation = math.deg(deg) + 90
– The +90 is because the rotation was originally built for an image with the cannon pointing
– right, not an image pointing upwards
if ( event.phase == “ended” ) then
cannonBall:setLinearVelocity(math.sin(math.rad(cannon.rotation))*200, math.cos(cannon.rotation))*-200)
end
end [import]uid: 82408 topic_id: 15607 reply_id: 57647[/import]

#5

email me the code, images etc… so I can see it run support@coronaremote.com [import]uid: 5354 topic_id: 15607 reply_id: 57658[/import]

#6

Oh by the way, I finished it, and am adding improvements to it. The cannon fires and rotates perfectly, and the cannon ball can interact with the other objects. Glad I figured this out. Cya :wink: [import]uid: 82408 topic_id: 15607 reply_id: 57791[/import]

#7

Hello,

I’m new to Corona SDK and LUA and I could use some help, I can’t solve this problem for a couple of days. I want to code this:

  1. one stick to be rotating permanently at certain speed - I figured that out

  2. and to fire some bullet on tap event - I figured that out to

This is the code:

[lua]centerX = display.contentWidth * .5
centerY = display.contentHeight * .5

– Physics
local physics = require(“physics”)
physics.start()
physics.setGravity( 0, 0 )

local rotationSpeed = 5
local stick
local bullet
local halfStick

local bg = display.newImageRect(“images/bg.png”, 570, 360)
bg.x = centerX
bg.y = centerY

stick = display.newImageRect ( “images/stick.png”, 25, 150 )
stick.x = centerX
stick.y = centerY
stick:setReferencePoint(display.CenterReferencePoint);

local stickkRotation = function ()
stick.rotation = stick.rotation + rotationSpeed
end

local function shootBullets(event)
bullet = display.newImageRect (“images/bullet.png”, 25, 27)
bullet.x = stick.x
bullet.y = stick.y
bullet.rotation = stick.rotation
physics.addBody(listic, “dynamic”, {density=1.0, friction=0.5, bounce=0.1})
local speed = 300
local velocity = {}
velocity.x = math.cos( math.rad( bullet.rotation - 90)) * speed
velocity.y = math.sin( math.rad( bullet.rotation - 90)) * speed
bullet:applyForce(velocity.x, velocity.y, stick.x, stick.y)

end

–Listeners
Runtime:addEventListener(“enterFrame”, stickRotation)
Runtime:addEventListener(“tap”, shootBullets);

[/lua]

The problem is that I don’t know how to set bullet to start from top of the stick (now it starts moving from center of the stick). I really don’t know how to solve that and I can’t lose any more time on that. So, I need a formula which calculates position of top of the stick and shoots bullet from there in the direction in which is the stick.

Could someone please help me with this?

#8

Hello,

I’m new to Corona SDK and LUA and I could use some help, I can’t solve this problem for a couple of days. I want to code this:

  1. one stick to be rotating permanently at certain speed - I figured that out

  2. and to fire some bullet on tap event - I figured that out to

This is the code:

[lua]centerX = display.contentWidth * .5
centerY = display.contentHeight * .5

– Physics
local physics = require(“physics”)
physics.start()
physics.setGravity( 0, 0 )

local rotationSpeed = 5
local stick
local bullet
local halfStick

local bg = display.newImageRect(“images/bg.png”, 570, 360)
bg.x = centerX
bg.y = centerY

stick = display.newImageRect ( “images/stick.png”, 25, 150 )
stick.x = centerX
stick.y = centerY
stick:setReferencePoint(display.CenterReferencePoint);

local stickkRotation = function ()
stick.rotation = stick.rotation + rotationSpeed
end

local function shootBullets(event)
bullet = display.newImageRect (“images/bullet.png”, 25, 27)
bullet.x = stick.x
bullet.y = stick.y
bullet.rotation = stick.rotation
physics.addBody(listic, “dynamic”, {density=1.0, friction=0.5, bounce=0.1})
local speed = 300
local velocity = {}
velocity.x = math.cos( math.rad( bullet.rotation - 90)) * speed
velocity.y = math.sin( math.rad( bullet.rotation - 90)) * speed
bullet:applyForce(velocity.x, velocity.y, stick.x, stick.y)

end

–Listeners
Runtime:addEventListener(“enterFrame”, stickRotation)
Runtime:addEventListener(“tap”, shootBullets);

[/lua]

The problem is that I don’t know how to set bullet to start from top of the stick (now it starts moving from center of the stick). I really don’t know how to solve that and I can’t lose any more time on that. So, I need a formula which calculates position of top of the stick and shoots bullet from there in the direction in which is the stick.

Could someone please help me with this?