Automatically change the position of objects when using different devices - lua

Question

I am still new to lua and corona (3 days to be exact) and I'm trying to my objects on the screen using multiple devices. From what I understand, to make the objects automatically reposition themselves, I need to get the screen size and do some calculation to it to make the necessary adjustment. Here's a sample of what I'm trying to do:
obj1 = display.contentWidth*0.50
This will then put my object to the middle of the screen but there are instances wherein this doesn't seem effective so my question is, what is a better approach to automatically reposition my objects? Especially objects that are no longer in the center of the screen.

Answer 1

I'm doing it in a different way. I think this may help you. As my opinion, just create multiplier values for width and height(according to which simulator you are coding in), and multiply your each width or height parameter with this(as below):
--------------------------------------------------------------------------
-- choosing xMultiplier and yMultiplier values --
--------------------------------------------------------------------------
local xMultiplier = display.contentWidth/320
local yMultiplier = display.contentHeight/480
--[[ I used 320 here because i'm using iPhone Simulator
(320 is the width of the simulator you are coding in)
I used 480 here because i'm using iPhone Simulator
(480 is the height of the simulator you are coding in)--]]
--------------------------------------------------------------------------
-- creating background and positioning it --
--------------------------------------------------------------------------
local bg = display.newImageRect("bg.png",320*xMultiplier,480*yMultiplier)
bg.x = 160*xMultiplier ; bg.y = 240*yMultiplier
--------------------------------------------------------------------------
-- creating object and positioning it --
--------------------------------------------------------------------------
local rect = display.newImageRect(0,0,50*xMultiplier,50*yMultiplier)
rect.x = 160*xMultiplier ; rect.y = 100*yMultiplier
--------------------------------------------------------------------------
Note: If you are using config.lua file in your project, this may not work.
Pros: This needs only one image.
Cons: It may affect the clarity of images in devices with high resolution. So choose an image with suitable resolution.
keep coding... :)

Answer 2

The way I do this is based off of the principle that things are going to positioned based on a side of the device or from the center. I'm going to use a horizontal app for this, btw.
Somethings need to be anchored to the left or right edges. Somethings need anchored to the top of the screen and other things need to be some distance away from center.
Consider this image:
The Home Icon and settings icon need to be a few pixels away from the left edge. They also need to be a few pixels down from the top. I would position these using a fixed number:
homeIcon.x = 32
homeIcon.y = 32
gearIcon.x = 32
gearIcon.y = 64 -- or whatever numbers they really are.
The score on the right needs to be a fixed distance away from the right edge and top:
scoreText.x = display.contentWidth - 64
scoreText.y = 32
The Turkey on the bottom's position shouldn't change based on the shape of the device's width, but could move based on the height of the device.
turkey.x = display.contentCenterX
turkey.y = display.contentHeight - 64
On an iPad which is less wide than an iPhone in this example, the home, gear and score buttons will end up closer to center. On an iPhone 5 or a wide screen Android, they spread out.
The example above doesn't really help on some of the centering ideas. I don't have a screen shot for this, but lets say you were laying out a login form for a game where you are collecting the Username and password and you had a submit button. You could position them like:
usernameField.y = display.contentCenterY - 64
passwordField.y = display.contentCenterY
submitButton.y = display.contentCenterY + 64
Then regardless of the height of the device, those UI elements would stay the same distance from the center making your form look good. If you used a fixed distance from the top, the form would move based on the size of the device. Here their positions stay the same.