Log

As mentioned in the previous section all following sections (including this one) are optional and were not covered in the original LibGDX tutorial. However, I recommend to read them as well because they are basic things that you will need in every game.
Without further ado let's jump into logging. Please refer to the official LibGDX documentation to learn more about logging. I will only focus on the LibKTX extensions.

---

So, what is the first thing we need to do? Correct! Update our project's build.gradle file and re-sync the project :)

        // ...
        api "io.github.libktx:ktx-app:$ktxVersion"
        api "io.github.libktx:ktx-collections:$ktxVersion"
        api "io.github.libktx:ktx-graphics:$ktxVersion"
+       api "io.github.libktx:ktx-log:$ktxVersion"
    }
}

After that we can already use the LibKTX log extensions. Please refer to the Why? section of this documentation as it already explains the benefits of using LibKTX for logging. In short, it addresses the unnecesarry string building, creation and vararg calls by introducing inlined lambdas which means that instead of Java's

if (Gdx.app.logLevel >= Application.LOG_DEBUG) Gdx.app.debug("someTag", "My message: " + someObject);

we get

debug("someTag"){ "My message: $someObject }

---

To demonstrate it in a real example we will update our GameScreen and log a debug message whenever we miss a raindrop and when the dispose method is called.
First we create a private toplevel log which is the fastest and best way to create a static log instance. The alternative would be a companion object which is not as performant as the private toplevel (refer to Christophe Beyls Kotlin's hidden costs talk).

+import ktx.log.logger

+private val log = logger<GameScreen>()

class GameScreen(val game: Game) : KtxScreen {
// ...

After that we can log anything related to our GameScreen file. We will add following two debug lines.

// ...
raindrops.iterate { raindrop, iterator ->
    raindrop.y -= 200 * delta
    if (raindrop.y + 64 < 0) {
        iterator.remove()
+       log.debug { "Missed a raindrop!" }
    }
    if (raindrop.overlaps(bucket)) {
        dropsGathered++
        dropSound.play()
        iterator.remove()
    }
}
// ...
override fun dispose() {
+   log.debug { "Disposing ${this.javaClass.simpleName}" }
    dropImage.dispose()
    bucketImage.dispose()
    dropSound.dispose()
    rainMusic.dispose()
}
// ...

To see our new debug lines we also need to adjust our DesktopLauncher to set the correct loglevel. This can be done anywhere but we will do it in the DesktopLauncher for now. The default loglevel is Info. We will set it to Debug.

object DesktopLauncher {
    @JvmStatic
    fun main(arg: Array<String>) {
        val config = LwjglApplicationConfiguration().apply {
            title = "Drop"
            width = 800
            height = 480
        }
        LwjglApplication(Game(), config).logLevel = Application.LOG_DEBUG
    }
}

And with that we are done with logging basics! I told you it will be short ;) The final code can be checked out with the 03-log branch.
Next we will introduce a better way of handling our assets like textures, music and sounds. Also, we will improve render performance by using a TextureAtlas to avoid texture swapping.