Monday, August 28, 2017

Summary of GSoC 2017

During the last three months I have worked on porting the game Mission Supernova to ScummVM, a project aiming to reimplement engines of point and click adventures for cross-platform support.

For the latest changes, see the commits to my fork.
Besides porting I also worked on the ScummVM launcher and fixed theme related bugs

The following lists features that are implemented:
  • Image and Text rendering
  • Audio playback of sounds and music
  • Animation system
  • GUI
  • Saving and restoring game state
  • Game logic converted to engine reimplementation

Most crucial engine components work but there is still work left to be done:
  • Translate the remaining strings to English
  • Implement dialog system
  • Fixing pesky bugs
  • Make it all work together in harmony

While this may be the end of GSoC 2017, my journey has just begun.
Thanks to everyone involved sharing their knowledge and providing help whenever needed. Also thanks to Google for giving the incentive and exposure to all those incredible projects. The experience of staring at hexdumps, deciphering disassembly and the communal effort has been invaluable to me.
I will keep contributing to the ScummVM project in the future beyond finishing my project (just you wait, Chewy!) and hope that some of you out there will find entertainment in my work.

Summary -- Week 11

SPOILERS IN VIDEO! (0:22 - 0:31)

As announced last week, the timer bugs are no more!
The original game used ticks of 18.2Hz instead of milliseconds for example, so while this little helper converted ticks to milliseconds it was not always easy to recognize what number actually represented a time value.
For instance, I assumed that a variable named time would most likely be the perfect candidate. Oh, how wrong I was. It actually stored the remaining days until the ship arrives at its destination. Do not ask how long it took me to figure this out although comparing time with energy should have made me wary.. (1,2,3)

Adjusting the brightness of the palette was more an issue of rendering order. While the function worked fine it either did a buffer swap too early or the brightness was restored to its previous state by the following draw call.
By removing most special cases it not only simplified the function but also fixed most issues. I did a side by side comparison with the original game and couldn't find any difference. (1)

What was different though is that I couldn't interact with anything in the ship's hold anymore. Apparently it hasn't been working for a while.. Originally an uninitialized object was identified by checking if its name string points to NULL but I misread it as a check if the first char is 0 (empty string). Unfortunately, objects without a name can still be valid what messed up the traversal of objects in a room. (1)

After running in circles for a while a few important features like RTL and save/load support were implemented. Unfortunately, state serialization still shows puzzling behavior that I haven't figured out how to solve yet. (1,2,3)

Friday, August 25, 2017

Summary -- Week 10

  • The biggest change this week was fixing the terminal next to the sleeping pods and the clearing of previous input. (1,2)
  • Also, the game text was converted to it's original encoding (CP437) to correctly render special characters. (1
  • A long standing rendering bug that caused certain sprites not to be rendered was finally found and fixed. (1)

There were a few smaller commits that will help to finally fix timing issues and a few rendering problems with dimming the ship's light next week.

Sunday, August 13, 2017

Summary -- Week 9

The remaining game logic has been implemented with a few exceptions but still needs to be thoroughly tested. (1, 2)
Speaking of testing, there are still bugs in the first act that need to be ironed out before a pull request can be issued like rendering artifacts and problems with the terminal next to the sleeping pods.

For next week, it is planned to fix up act 1 and to finish implementing the dialog system as the second and third act are now available for testing. 

Monday, August 7, 2017

Summary -- Week 8

This week was about implementing the terminal in the sleeping cabin room, adding the death screen and clean up.

Unfortunately it's still quite buggy and needs more investigation. Currently, the game restarts on death to the beginning as there's no full implementation of save/load yet.

For next week I will keep implementing missing game code for the remaining two acts and make it just compile for now.
Most key functionality is already implemented but with the other acts in the engine the dialog functionality can finally be tested.

Tuesday, July 25, 2017

Summary -- Week 7

So most of the week was spent on rewritting the game loop to implement animations as shown above and fixing the bugs introduced by it..
The animation system is simply implemented by setting a timer that when it expires causes the room specific animation() function to be called. (1, 2, 3, 4)
Besides that,

An interesting discovery for me was that although the text rendering code is correct it shows artifacts when drawing umlauts. As the game strings were copied directly from the cp437 encoded source I expected the character value to be encoded in a single byte as characters in extended ASCII don't exceed 0xFF. What I didn't consider is that UTF8 is only backwards compatible to basic ASCII (0x00 - 0x7F) and anything above takes at least two bytes, what causes the corruption as seen above ("Triebwerke funktionsunfähig"). That's why umlauts in the German original will be substituted by their equivalent octal value as already done here.

For the coming days the first act should be made playable by implementing edit() so the sleeping cabin section works correctly and adjust the game loop for dying and implement the 'death screen'.
After that implementing the remaining game logic takes priority especially now that the animation system is working.

Tuesday, July 18, 2017

Summary -- Week 6

Sorry for the delayed report this week but I really wanted to add a video finally walking through the empty hallways of the starship Supernova. Moreover...

ūüéČ The GUI is finally working! ūüéČ

Probably the most noticeable improvement is that GUI is now actually rendered correctly and interaction with the environment is finally possible without everything glitching out. Although, there are still issues with Give and Use command that will be addressed next.
Besides the GUI there have been improvements on every front.
  • Wrapping GUI elements in a state class (1, 2, 3)
  • Fixing font rendering
  • Correctly handling and rendering object state (1, 2, 3, 4)
  • Improvingn mouse input handling (1, 2)

Coming up next will be implementing timers for handling events and animations. There have been talks about starting translating but depending on how things go it either has to be pushed back or will have a lower priority.
Of course fixing a bunch of bugs along the way would be nice too :)