HaxeFlixel Tutorial – Camera Zoom

@mikeevmm tweeted me early this month and noted that there are some problems with FlxCamera.

Here are some known issues I could identify:

  1. Camera doesn’t follow well when zoomed.
  2. Objects start disappearing when zoom is less than 1.

The problems above are apparent (as of writing) even in the FlxCamera demo.

There’s an article by Bullet Time Ninja that discusses and resolves the camera issue, but it’s from 2011 and uses Flixel (not HaxeFlixel), so the result may differ.

Today’s tutorial will attempt to resolve the first problem stated above. If there is a solution for the second problem, I’ll write a tutorial to address that next time. :)

Setup

As usual, let’s setup a new HaxeFlixel template project for testing:

Code

First, let’s set an arbitrary resolution of the game in the Main.hx file:

Now, let’s go into MenuState.hx (the default entry point for the game) and create a large-enough level with a movable character:

Now if you run the game with lime test neko , you’ll get a player that can move around a placeholder map, and the camera follows it, within the map’s bounds (btw, yes, there is no collision logic):

licecap-cam-1

Now let’s add some debug controls to recreate the problems mentioned at the beginning of the article above:

Now if you test the game — Zooming in and out will only zoom the camera’s viewport. The camera still “follows the player”, but not in a way you would expect:

licecap-cam-2

When we use  camera.zoom , it seems we’re actually resizing the camera’s viewport. So how can we fix this? With my limited knowledge, I’d assume the solution is to reposition and resize the camera every time its zoom is changed.

Before we do that, let’s add more debug input into the code so we can later understand what needs to be used to fix the problem:

Now if you play around with the debug keys above, you’ll notice the following points:

  • Changing the camera’s x  or y  value will move the viewport’s origin (top-left corner).
  • Changing the camera’s width  or height  value will increase/decrease the viewport’s size.
  • Changing the viewport size doesn’t seem to update the tilemap’s size, until we use level.updateBuffers() (by pressing P).
  • The camera’s deadzone (when following the player) isn’t updated, until we re-follow the player (by pressing O).

Resolving Camera Zoom issue

After some testing with the debug keys above, it seems we can combine the techniques and resolve the zoom issue, by writing the following code:

Now when you zoom in or out, the camera is centered and the player’s deadzone is updated:

licecap-cam-3

Notice that the player will get cropped when moving out of the map’s bounds. That’s because we used  FlxG.camera.setBounds() . If you modify the following lines:

The player can now freely move around in the camera without being cropped, at the expense of not having any map boundaries:

licecap-cam-4

To top things off, let’s use Bullet Time Ninja’s technique in lerping the camera’s zoom:

And the result:

licecap-cam-5

It’s not perfect, but I think this should be enough for most camera-zooming issues. This concludes the tutorial on zooming the camera.

2 thoughts on “HaxeFlixel Tutorial – Camera Zoom

    • WY Leong says:

      Hi sruloart, thanks for the pointer. I can’t believe I missed that! I’ll make another quick post to address this next time. 😀 I will study the API a little more too.

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