Why Mega Drive games showed no picture

I fixed an issue where Mega Drive games showed an error instead of a picture on Android. The app had reserved too little space to hold the picture data.

While checking each system on an Android tablet, I found that the Mega Drive picture would not appear. I ran a test program I had made, but got an error message instead of the game screen.

Before displaying a game, the app sets aside space to temporarily hold its picture data. The Mega Drive picture size had been recorded as smaller than it really was, so the app reserved too little space. The complete picture would not fit, causing the error.

iOS handles picture data differently, so it did not have the same problem. The existing automated tests did not check whether Android had room for the whole picture. All the tests passed, yet the picture still failed to appear on the tablet.

I corrected the recorded picture size so the app would reserve enough space. To catch the same mistake, I also added a check for the other systems that run games using the same engine as Mega Drive: their actual pictures must not exceed the sizes recorded in the app.

After the fix, I ran the test program again on the same tablet and checked its picture output. This was only a simple test program, though. Long play sessions with actual games still need separate testing.