# Creating a bouncing ball with a set velocity

I’ve seen many examples about how to make an object bounce around on a screen, but i still can’t figure out how to have the user “flick” the screen and have the ball bounce at a certain speed. Im used an object to create the ball so I think it has something to do with linearVelocity but i’m not sure. It always goes in one direction that way.

the touch object has a lot of information in in (check the online help).

This includes touch.deltaX and touch.deltaY, which tell you how much the finger moved in the x and y direction since last redraw. If you change your x, y velocity to these values, your ball will react to finger flicks

. @evanlws12 Here is something I wrote a while back. I flick an object at another object. Maybe this will help you.

``````
supportedOrientations(PORTRAIT)
displayMode(FULLSCREEN)
lineCapMode(SQUARE)

function setup()
tab={}
rcount=0
scount=0
screated=false
rcreated=false
createEdges()
end

function draw()
background(40, 40, 50)
showLines()
showText()
drawEdge()
drawRandom()
drawShots()
end

function showLines()
stroke(0,255,0)
strokeWidth(4)
line(0,300,WIDTH,300)
stroke(255,0,0)
strokeWidth(20)
line(300,HEIGHT,450,HEIGHT)
end

function showText()
fontSize(40)
fill(255,0,0)
if not rcreated then
text("Double tap screen for red ball.",WIDTH/2,HEIGHT/2+300)
end
str=string.format("Goals %4d            Shots %4d",rcount,scount)
fontSize(20)
fill(255)
text(str,WIDTH/2,HEIGHT/2-50)
str=string.format("Score %6.4f         (Goals / shot)",rcount/scount)
text(str,WIDTH/2,HEIGHT/2-100)
text("Flick shots from below this line to push",WIDTH/2,320)
text("the red ball through the red line at the top.",WIDTH/2,280)
end

function createEdges()
e1=physics.body(EDGE,vec2(0,0),vec2(0,1200))
e1.type=STATIC
e2=physics.body(EDGE,vec2(WIDTH,0),vec2(WIDTH,1200))
e2.type=STATIC
e3=physics.body(EDGE,vec2(0,HEIGHT),vec2(300,HEIGHT))
e3.type=STATIC
e4=physics.body(EDGE,vec2(450,HEIGHT),vec2(WIDTH,HEIGHT))
e4.type=STATIC
end

function drawEdge()
stroke(255)
strokeWidth(10)
line(0,0,0,HEIGHT)
line(WIDTH,0,WIDTH,HEIGHT)
line(0,HEIGHT,300,HEIGHT)
line(450,HEIGHT,WIDTH,HEIGHT)
end

function createRandom()
r1=physics.body(CIRCLE,30)
r1.gravityScale=.5
r1.x=math.random(WIDTH)
r1.y=HEIGHT-200
rcreated=true
end

function drawRandom()
if rcreated then
strokeWidth(0)
fill(255,0,0)
ellipse(r1.x,r1.y,60,60)
destroyRandom()
end
end

function destroyRandom()
if r1.y < 0 or r1.y>HEIGHT then
rcreated=false
tab={}
if r1.y>HEIGHT then
rcount = rcount + 1
end
r1:destroy()
end
end

function createShots()
scount = scount + 1
z=#tab+1
tab[z]=physics.body(CIRCLE,15)
tab[z].gravityScale=-.1
end

function drawShots()
fill(255)
for z=1,#tab do
ellipse(tab[z].x,tab[z].y,30,30)
end
destroyShots()
end

function destroyShots()
for z=1,#tab do
if tab[z].y > 1000 or tab[z].y < 0 then
tab[z]:destroy()
table.remove(tab,z)
return
end
end
end

function touched(t)
if not rcreated then
if t.tapCount==2 then
createRandom()
end
return
end
if t.state==BEGAN and t.y< 300 and rcreated then
createShots()
screated=true
z=#tab
tab[z].x=t.x
tab[z].y=t.y
x1=t.x
y1=t.y
end
if t.state==MOVING and screated then
if #tab>0 then
z=#tab
tab[z].x=t.x
tab[z].y=t.y
end
end
if t.state==ENDED and screated then
screated=false
if #tab>0 then
z=#tab
x2=t.x
y2=t.y
xd=x2-x1
yd=y2-y1
tab[z].linearVelocity=vec2(xd*5,yd*5)
end
end
end

``````

There’s a tutorial out here
https://bitbucket.org/TwoLivesLeft/core/wiki/TouchTutorial but it doesn’t include physics objects

That tutorial is worth reading for the last bit about flicks where it explains why not to just use the last touch information.

@dave1707 I do like the game! I do see you made the linear velocity (x2-x1)*5 however so when the user flicks very slowly, the ball also moves slowly. I’m still trying to figure out if there is a way that no matter how slowly the flick is, the ball moves at the same speed?

.@evanlws12 Replace the code “if t.state==ENDED” with the code below. Change the number 500 in the code below to get the speed that you want. The larger the number the faster it will go, but it should go at the same speed no matter how fast or slow you flick.

``````
if t.state==ENDED and screated then
screated=false
if #tab>0 then
z=#tab
x2=t.x
y2=t.y
xd=x2-x1
yd=y2-y1
s=500/math.sqrt(xd^2+yd^2)
tab[z].linearVelocity=vec2(xd*s,yd*s)
end
end

``````

It works! Thank you!