JSON data file performance

Solar2D Lua Language
#1

I’m using Twine 2 to create a ‘choose your own adventure’ type story, and I’m outputting the text and structure as a JSON file. I’m reading/decoding the JSON file and then reading from the Lua table (I think, I might be mistaken) with each page render to get the text.

The issue I find is that the pause before rendering is noticeable (in the simulator) and the scrollview is sluggish compared to getting text from a Lua table. Can anyone advise how I can improve this? How would I go about copying out relevant data from the JSON file to a Lua table (if that would lead to better performance)? Any tips would be greatly appreciated.

I’m not sure if ‘t’ below is a Lua table, or why using that would lead to slower performance.

Here’s an excerpt of what i have:

[lua]

local json = require “json”

–Read/decode the json file

local jsonFile = function( filename, base )

if not base then base = system.ResourceDirectory; end

local path = system.pathForFile( filename, base )

local contents

local file = io.open( path, “r” )

if file then

  contents = file:read( “*a” )

  io.close( file )

end

return contents

end

– Create Lua table from JSON file?

local t = json.decode( jsonFile( “data2.json” ) )

– An example of accessing a data value from t

print (t[“passages”][2][‘text’])

[/lua]

Once I have access to the JSON text values I’m rendering them inside a scrollview:

[lua]

local group = display.newGroup()

local scrollView = widget.newScrollView

{

   top = display.screenOriginY,

   left = 0,

   width = display.actualContentWidth,

   height = display.actualContentHeight,

   scrollWidth = display.actualContentWidth,

   scrollHeight = 8000,

   backgroundColor = { 0.05, 0.05, 0.05 },

   --hideBackground = true,

   horizontalScrollDisabled = true,

   friction = 0.95,

   hideScrollBar = true,

   bottomPadding = 30

}

local options = 

{

   text = (t[“passages”][#num][“text”]),

   width = display.actualContentWidth-30,

   font = native.newFont( “Paciencia-Regular”, 32 ),

   fontSize = 15,

   align = “left”,

   parent = group

}

local paragraph = display.newText( options )

paragraph.anchorX = 0.5

paragraph.anchorY = 0

paragraph.x = display.actualContentWidth/2

paragraph.y = 380

paragraph:setFillColor( 0.95, 0.95, 0.95 )

scrollView:insert( paragraph )

[/lua]

#2

So are you using json.decode every time you draw a new scrollView, or just once at the beginning?

‘t’ is a lua table, but if you’re re-populating it each time that might cause a delay. Might be better to import all your text into lua tables right at the beginning.

#3

Hi Nick, thank you very much for your advice. I moved the json.decode to the beginning and that helped. I might have another issue because I notice the Corona simulator seems to slow down if I keep reloading rather than closing down and restarting - but you put me on the right track.

#4

There is no hit in loading hundreds of JSON entries into a local table and referencing that throughout your project.  Avoid file I/O if possible and only do it once.

If your JSON data file is massive (i.e. thousands of rows of text) then lazy load it on demand for better performance.

#5

Hi Adrian, thanks. Maybe a silly question but what do you mean by ‘lazy load’?

Once the JSON data is in a Lua table, I’m getting values, for example, by:

[lua]

local rawText = _G.t[“passages”][number][“text”]

[/lua]

Where ‘number’ is a variable, e.g. ‘2’.

(yes, I’m using _G - I could’t get it to work otherwise.)

And at the risk of straying from my original question, any idea how I can check if a value exists in the table?

I’m trying:

[lua]

if ( _G.t[“passages”][number][“links”][3][“link”] ~= nil )

   then optionThreeExists = true

end

[/lua]

but this gives the following error:

Attempt to index field ‘?’ (a nil value)

#6

So are you using json.decode every time you draw a new scrollView, or just once at the beginning?

‘t’ is a lua table, but if you’re re-populating it each time that might cause a delay. Might be better to import all your text into lua tables right at the beginning.

#7

Hi Nick, thank you very much for your advice. I moved the json.decode to the beginning and that helped. I might have another issue because I notice the Corona simulator seems to slow down if I keep reloading rather than closing down and restarting - but you put me on the right track.

#8

There is no hit in loading hundreds of JSON entries into a local table and referencing that throughout your project.  Avoid file I/O if possible and only do it once.

If your JSON data file is massive (i.e. thousands of rows of text) then lazy load it on demand for better performance.

#9

Hi Adrian, thanks. Maybe a silly question but what do you mean by ‘lazy load’?

Once the JSON data is in a Lua table, I’m getting values, for example, by:

[lua]

local rawText = _G.t[“passages”][number][“text”]

[/lua]

Where ‘number’ is a variable, e.g. ‘2’.

(yes, I’m using _G - I could’t get it to work otherwise.)

And at the risk of straying from my original question, any idea how I can check if a value exists in the table?

I’m trying:

[lua]

if ( _G.t[“passages”][number][“links”][3][“link”] ~= nil )

   then optionThreeExists = true

end

[/lua]

but this gives the following error:

Attempt to index field ‘?’ (a nil value)