Timer module

[zacharycarter]

Continuing discussion from : https://github.com/zacharycarter/zengine/issues/13

[define-private-public]

My opinion is that maybe we should have some sort of global object that anything can read from. e.g:

type
  ZApp* = object
    totalTicks*: int          # Total amount of elapsed ticks for the app
    updateDeltaTicks*: int    # Ticks since the last logical update
    drawDeltaTicks*: int      # Ticks since the last draw

# (somewhere else in the code...)
zengine.app = ZApp()

# (In the main update/draw loops...)
zengine.init(...)
while running:
  zengine.app.nextUpdateFrame()
  # ... game logic here

I'd also like to throw my stopwatch module in the running to facilitate this. AFAIK, it should run on mobile platforms since it tries to use Nim code, but I'm not 100% if it does as I haven't tested it.

[zacharycarter]

I'm trying to refrain from having globals the user has to manage, thus keeping everything very module based and just exposing functions to the user - if that makes sense. How about another module called timer which holds these globals and exposes a function called nextUpdateFrame() or whatever? Is there a reason you'd prefer to have a global object?

It's just a bit different from the current implementation is all I'm trying to get at.

[define-private-public]

eh, I just like objects.

[define-private-public]

I'd like to bump this ticket and give it the highest priority to work on right now. As I'm starting to work on sprite rendering I'll need this for when it comes time to animate, which is going to be pretty soon.

[define-private-public]

I'd also like to say I'd like to deal with deltas as floating point numbers. E.g. at 60 FPS, we'd give them a value of 0.016666666667 each frame. I like this because If someone says, "I want my player to move five units per second." It's easier to do this: player.x += speed * delta instead of player.x += speed * (delta / 1000.0) (assuming we use milliseconds if we go with hard ints).

[zacharycarter]

I'll work on this after work today.

[zacharycarter]

What do you think about something like -

import sdl2

var 
  startTime, currentTime, previousTime, updateTime: float64
  ticks: uint

proc getTicks*(): uint =
  ticks

proc getDeltaTime*(): float64 =
  updateTime

proc getTimeSinceLastTick*(): float64 =
  currentTime - previousTime

proc getTimeElapsed*(): float64 =
  currentTime - startTime

proc getTime*(): float64 =
  currentTime

proc tick*() =
  currentTime = float64(sdl2.getPerformanceCounter()*1000) / float64 sdl2.getPerformanceFrequency()
  updateTime = currentTime - previousTime
  previousTime = currentTime
  inc(ticks)

proc init*() =
  startTime = getTime()
  currentTime = startTime

Anything you'd like to see added? I don't understand this whole logic tick component you referred to in your example. I figured that'd be left up to the user to implement?

[define-private-public]

Yeah, this looks pretty good right now. A few tiny things:

1. I'd mark each of the procs with a {.inline.} pragma so we get a tiny performance boost, since these will probably be called a lot.
2. Does sdl2.getPerformanceFrequency() return the same value each time it's called? If so, we should cache it in another variable at the init() step
3. Isn't getTimeSinceLastTick() a little redundant?
4. I don't think getTime() is needed. Unless someone wants the time since application start and not tick time start. I'll leave decision up to you.
5. Maybe some renamings:

• getTicks() -> totalTicks(): Drop the get and better define what the proc does by the name.
• getDeltaTime() -> deltaTime(): Drop the get.
• init() -> start()/startTicking().: start() is a really ambiguous name.

We also need some documentation to explain what is the different between a tick and a delta and how to use what functions in the game loop.

[define-private-public]

I saw your commit and left some notes inline. Please take a look at them:

https://github.com/zacharycarter/zengine/commit/20751d70870a372cb234633b7b8a3cdc01076771

[define-private-public]

As a side note, next time can you make a separate branch then make a PR for it instead? I'd rather do review there than do it inline with a commit in master.

[define-private-public]

Hey, I tried out what you have put in the timer module right now and it's kind of incorrect.

E.g. I though we were going to have the deltaTime() function return time in seconds. But instead, each tick it's giving me 16.6667 per tick. It should be 0.01666667. I'll post a PR tomorrow that uses this behavior and better defines the documentation. I'd also like to adjust the names to fit what I have above, but I'll keep what you've got.

You might need to go back and adjust your examples, though it shouldn't be too hard.