Having an issue with dragging

I'm trying to make a basketball that can bounce off the ground but can also be dragged. However, after adding a bunch of code from the DragPlatforms source code and making it applicable to the basketball, the screen on my simulator just shows black. Why is this? Here's all the drag code I am using:

local function startDrag( event )
        local t = event.target
 
        local phase = event.phase
        if "began" == phase then
                display.getCurrentStage():setFocus( t )
                t.isFocus = true
 
                t.x0 = event.x - t.x
                t.y0 = event.y - t.y
                
                event.target.bodyType = "kinematic"
                
                event.target:setLinearVelocity( 0, 0 )
                event.target.angularVelocity = 0
 
        elseif t.isFocus then
                if "moved" == phase then
                        t.x = event.x - t.x0
                        t.y = event.y - t.y0
 
                elseif "ended" == phase or "cancelled" == phase then
                        display.getCurrentStage():setFocus( nil )
                        t.isFocus = false
 
                                event.target.bodyType = "dynamic"
                        end
 
                end
        end
 
        return true
end
 
basketball:addEventListener( "touch", startDrag )

just check your terminal window for error messages...

I've figured out how to use terminal finally. I tried using terminal on the program that was having issues, and got this message: Syntax error: ... 'eof' expected near 'end'

I don't entirely understand. I know that something is expected to be closer to the 'end' function, but what does the 'eof' mean?

P.S. 'eof' is in the < > brackets.

I just replaced all my code with the drag code from "TimeAnimation". It now works, but the ball is behaving erratically. I try dragging it and it begins to fall with gravity or fly upwards as though gravity was negative (though it somewhat stays with my touch while I'm moving the mouse). Perhaps it's not entirely kinematic while I'm dragging? Here's my drag code (it's really long, just so you know):

function onMoveCircle(event) 
        local timePassed = event.time - lastTime
        lastTime = lastTime + timePassed
 
        speedY = speedY + gravity
 
        basketball.x = basketball.x + speedX*timePassed
        basketball.y = basketball.y + speedY*timePassed
 
        if basketball.x >= screenW - basketball.width*.5 then
                basketball.x = screenW - basketball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        elseif basketball.x <= basketball.width*.5 then
            basketball.x = basketball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        elseif basketball.y >= screenH - basketball.height*.5 then
                basketball.y = screenH - basketball.height*.5 
                speedY = speedY*friction
                speedX = speedX*friction
                speedY = speedY*-1  --change direction  
        elseif basketball.y <= basketball.height*.5 then
                basketball.y = basketball.height*.5
                speedY = speedY*friction
                speedY = speedY*-1 --change direction     
        end
end
        
-- A general function for dragging objects
local function startDrag( event )
        local t = event.target
        local phase = event.phase
 
        if "began" == phase then
                display.getCurrentStage():setFocus( t )
                t.isFocus = true
 
                -- Store initial position
                t.x0 = event.x - t.x
                t.y0 = event.y - t.y
                                                
                -- Stop current motion, if any
                Runtime:removeEventListener("enterFrame", onMoveCircle)
                -- Start tracking velocity
                Runtime:addEventListener("enterFrame", trackVelocity)
 
        elseif t.isFocus then
                if "moved" == phase then
                                        
                        t.x = event.x - t.x0
                        t.y = event.y - t.y0
 
                elseif "ended" == phase or "cancelled" == phase then
                        lastTime = event.time           
 
                        Runtime:removeEventListener("enterFrame", trackVelocity)
                        Runtime:addEventListener("enterFrame", onMoveCircle)
 
                        display.getCurrentStage():setFocus( nil )
                        t.isFocus = false
                end
        end
 
        -- Stop further propagation of touch event!
        return true
end
 
function trackVelocity(event) 
        local timePassed = event.time - prevTime
        prevTime = prevTime + timePassed
        
        speedX = (basketball.x - prevX)/timePassed
        speedY = (basketball.y - prevY)/timePassed
 
        prevX = basketball.x
        prevY = basketball.y
end
 
basketball:addEventListener( "touch", startDrag )
Runtime:addEventListener( "enterFrame", onMoveCircle )

cannot see the physics part of ur game.. can I see the addbody code for the basketball ?

Sure. I'll give you everything before the drag code:

local physics = require("physics")
physics.start()
system.activate( "multitouch" )
 
basketball = display.newImage( "Basketball.png" )
basketball.x = display.contentWidth / 2; basketball.y = display.contentHeight / 2
basketball.width = 100; basketball.height = 100
 
physics.addBody( basketball, { density = 1, bounce = 0.5, radius = 45 } )
 
print( "basketball" )
 
ground = display.newImage( "sludge.tif" )
ground.x = display.contentWidth / 2; ground.y = 550
 
physics.addBody( ground, "static", { density = 1, bounce = 0.1 } )
 
physics.setDrawMode( "hybrid" )

try putting
t.bodyType ="static" in began phase and t.bodyType ="static" in ended phase

I have seen the code that you have posted... and it should work without using physics... just copy the below code and try running it

local screenW, screenH = display.stageWidth, display.stageHeight
local friction = 0.8
local gravity = .9
local speedX, speedY = 0, 0
local prevX, prevY = 0, 0
 
local ball = display.newCircle( 0, 0, 25)
ball:setFillColor(255, 255, 0)
ball.x = screenW*.5
ball.y = 20
 
function onMoveCircle(event) 
        speedY = speedY + gravity
 
        ball.x = ball.x + speedX
        ball.y = ball.y + speedY        
 
        if( ball.x >= screenW - ball.width*.5 ) then
                ball.x = screenW - ball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        elseif( ball.x <= ball.width*.5) then
            ball.x = ball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        end
        if( ball.y >= screenH - ball.height*.5 ) then
                ball.y = screenH - ball.height*.5 
                speedY = speedY*friction
                speedX = speedX*friction
                speedY = speedY*-1  --change direction  
        elseif( ball.y <= ball.height*.5 ) then
                ball.y = ball.height*.5
                speedY = speedY*friction
                speedY = speedY*-1 --change direction     
        end
end
 
-- A general function for dragging objects
local function startDrag( event )
        local t = event.target
 
        local phase = event.phase
        if "began" == phase then
                display.getCurrentStage():setFocus( t )
                t.isFocus = true
 
                -- Store initial position
                t.x0 = event.x - t.x
                t.y0 = event.y - t.y
                                
                -- Stop current motion, if any
                Runtime:removeEventListener("enterFrame", onMoveCircle)
                -- Start tracking velocity
                Runtime:addEventListener("enterFrame", trackVelocity)
 
        elseif t.isFocus then
                if "moved" == phase then
                        t.x = event.x - t.x0
                        t.y = event.y - t.y0
 
                elseif "ended" == phase or "cancelled" == phase then
                        display.getCurrentStage():setFocus( nil )
                        t.isFocus = false
                        
                        Runtime:removeEventListener("enterFrame", trackVelocity)
                        Runtime:addEventListener("enterFrame", onMoveCircle)
 
                end
        end
 
        -- Stop further propagation of touch event!
        return true
end
 
function trackVelocity()        
        speedX = ball.x - prevX
        speedY = ball.y - prevY
 
        prevX = ball.x
        prevY = ball.y
end                     
 
ball:addEventListener("touch", startDrag)
Runtime:addEventListener("enterFrame", onMoveCircle)

I figured it out. Using the t.bodyType things you gave me above, I was able to get it to work so that it would be static while I was dragging and dynamic when I let go. Thanks for your kind help! ;) Hope a lot of people have someone like you to help them out when they need it.

views:1989 update：2011/10/4 17:12:07


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