dunai-examples: Convert examples from SDL1 to SDL2

[ivanperez-keera]

SDL 1 is deprecated. It seems to no longer compile well with modern versions of GHC.

Porting the examples to SDL 2 would make them more relevant to current developers, and keep our CI infrastructure working well.

[ivanperez-keera]

Help is sought for this. There are four modules that use SDL:

dunai-examples/bouncingball/BouncingBall.hs
dunai-examples/classicfrp/GTest.hs
dunai-examples/classicfrp/Test.hs
dunai-examples/list/BouncingBall.hs

If someone is able to work on this, please do the following:

• Send a PR that references this issue.
• Add one commit to upgrade each of the examples. Make sure each of those commits updates both the Haskell code and the corresponding cabal file.
• For each commit, add the following commit message, adjusting <NAME_OF_EXAMPLE> to the example you are modifying:

dunai-examples: Upgrade example to use SDL2. Refs #446.

SDL 1 is deprecated, and no longer maintained. To keep the example
working with more modern versions of packages in the Haskell ecosystem,
this commit ports <NAME_OF_EXAMPLE> to use SDL2.

• Add another commit that upgrades the .travis.yml file in the top-level directory to install the SDL2 development libraries in the CI server (see line https://github.com/ivanperez-keera/dunai/blob/develop/.travis.yml#L27). Use the following commit message:

dunai: Upgrade CI script to use SDL2. Refs #446.

SDL 1 is deprecated, and no longer maintained. All examples have consequently
been upgraded to use SDL2. This commit updates the CI installation script to
install the SDL2 development libraries instead of the SDL 1.2 version, to keep
the job working.

• Add one final entry in dunai's CHANGELOG (https://github.com/ivanperez-keera/dunai/blob/develop/dunai/CHANGELOG), under the last line of the currently open block (

  dunai/dunai/CHANGELOG

  Line 2 in 04c1dc3

  * Increase upper bounds on filepath, tasty, time, hlint (#448).

  ), with the text:
  Upgrade CI script to use SDL2 (#446).
• Commit that change to the changelog in a separate commit, with the following message:
  `dunai: Document changes in CHANGELOG. Refs dunai-examples: Convert examples from SDL1 to SDL2 #446."

EDIT: Two more steps added to upgrade the travis file too.

[mchav]

Thanks for the clear instructions. I'll start working on the bouncing ball example to start.

[ivanperez-keera]

Great! Feel free to send a PR when you have something you want me to take a look at, or just ask any questions you have.

[mchav]

The example dunai-examples/list/BouncingBall.hs doesn't seem to work.

1. You can't cabal run in the directory because it's not part of cabal.project.
2. It doesn't compile unless you remove the type signatures

BouncingBall.hs:31:15: error:
    • Couldn't match type ‘Identity’ with ‘IO’
      Expected: bearriver-0.14.11:FRP.BearRiver.InternalCore.SF
                  IO (Float, Float, Bool, Bool) [(Float, Float)]
        Actual: MSF
                  (ClockInfo Identity) (Float, Float, Bool, Bool) [(Float, Float)]

3. Even after all this the example freezes on mouse press.

Will fix this example as I port it.

[ivanperez-keera]

2. is related to bearriver: the function reactimate is API-incompatible #454.

[ivanperez-keera]

I think sometimes the CI build job is not completing for this reason:

haskell-game/sdl2#310

[mchav]

Thanks for addressing that.

Figured out the cause of 3. We have to use notYet here to delay the switching event. Is this the right intuition or am I missing something here?

[ivanperez-keera]

Hmm. Does that happen also with SDL1?

[mchav]

Yes. The example as is doesn't work. Both in SDL1 and when ported to SDL2. There seems to be an infinite loop when switching.

[ivanperez-keera]

Ok. Let me try and reproduce that.

In the meantime, I've sent a patch to the sdl2 project to get sdl2 compiling with older versions of GHC: haskell-game/sdl2#311. That should partly address the issue compiling in the CI server.

[ivanperez-keera]

The sdl2 patch has now been merged.

I don't know when the sdl2 project plans to make a new release, but we can for now use the github repo to test that everything works.

[mchav]

Did you manage to reproduce 3?

[ivanperez-keera]

Just to document things here too: I was able to reproduce (3) and we created a separate issue to track that error (#457 ), which @mchav just fixed (#458) .