Libgdx Hud with two stages

Question

I have an app that's currently working with a single stage but i need to add a side display/section as a HUD, with scores/lives etc on it, so that the HUD is on the left, and the main hand screen on the right. The main game screen will be fixed and will not move around.

From researching I've found a couple of solutions.

1 - two stages 2 - a group with two groups to it, possibly using a horizontalgroup 3 - two cameras one stage 4 - one stage, one camera, but changing the position of the camera for each set of actors.

I think, option 1 is my preference, but i have some questions.

• Do stages always fill the whole screen, or can i start then where i want? This would make it easier for the right hand screen to calculate positions based on 0,0 of that screen rather than always having to add the width of the HUD on to any calculations.
• Do i need to work about viewports? Currently I'm not using one (which i think means my stage is set to scaling by default) but nothing looks stretched as a result of this. I don't know much about viewports, but there always seems to be a compromise to be made with them, i.e. black bars top or sides.
• If I have two stages, do they each have their own camera? Do I need to with about this? Can I possibly aim the right hand camera at an offset so i can still draw things from 0,0 with that being the bottom left corner of the right stage, not the whole screen?

Finally, off topic, I am a little confused about spritebatch. I'm not currently using one, because I use a stage. Is that OK, or should i still be using one in conjunction with a stage somehow? And add all my actors to that?

Answer 1

It I understand correctly, you're using scene2d for your game world and also for your HUD. And the HUD doesn't overlay the game world, but rather uses its own portion of the screen exclusively.

Stages do not always fill the whole screen. They have no concept of filling or not filling anything, because they can have objects that are being drawn off screen. However, they are clipped to a rectangle defined by their Viewport.

In your case, it seems you need two Viewports, and therefore, two stages. You say you aren't using a Viewport, but you are...Stage automatically creates its own ScalingViewport that's set up like a StretchViewport. (ScalingViewport is not mentioned in the documentation, which is out of date.) StretchViewport is usually bad because your game will be distorted to fit whatever the aspect ratio of the device is.

ExtendViewports do not cause black bars as long as you don't set a max width/height on them and I think are usually the best choice for any game world view.

You can set your two Viewports to cover specific parts of the screen that you calculate yourself. Since this is a specialized case, I think you will have to directly subclass the Viewport class (not one of its subclasses) and manipulate each of them using viewport.setScreenBounds(...).

Regarding your last question: yes, each of the two stages has its own Viewport, and each Viewport has its own camera. Once you set up your two Viewports to each have their own portion of the screen, you can also set them to treat their respective bottom left corners as 0,0.