We worked rigorously to make these apps. As mentioned in above posts, we used Corona SDK for our apps.
Yes, its not easy but with careful planning it should be possible. For example, while there are other online tools to resize the icons (Usually we make one 1024*1024 icon and then resize it to various smaller sizes) , we just donot want to waste time there.
A quick math - If I spend 10-15 minutes to resize my icons to various sizes, its takes around 4000 minutes for my 300+ apps. We definitely do not want to spend so much effort of 4000 minutes on just resizing our icons. So, we wrote a small Imagemagick script in 10 minutes that will resize the icons in less than 5 seconds and I can rerun it as many time as I want.
Another example is we want to capture the screenshots of the app for some other purpose.We wanted to capture 7-9 screenshots per app. So, played the app on the emulator and written a quick screenshot taker code that takes screenshots for every click on my mouse and then it process the jpeg image and just gives me the screenshot of my emulator. So, to get 7-9 screenshots of 300 apps each, it would be close to 3000 screenshots but all done with just 1 mouse click per screenshot.
Like this, we have automated every piece of work that has a repetition.
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