ScreenSpaceEventHandler support for multiple KeyboardEventModifier keys at once

[Bob-vdV]

Feature

Currently the ScreenSpaceEventHandler can only listen for mouse events with either Alt, Shift or Ctrl modifier keys.

It would be nice to be able to add a listener for when multiple modifier keys are held at the same time, like this:

const listener = () => {console.log("SHIFT and ALT are held")}

screenSpaceEventHandler.setInputAction(
  listener, 
  ScreenSpaceEventType.LEFT_DOWN, 
  [KeyboardEventModifier.ALT, KeyboardEventModifier.SHIFT]
)

[jjspace]

Thanks for the issue @Bob-vdV, I definitely agree this could be a useful thing to have.

The current handler basically just keeps a map of key+[modifier] and their handlers. It probably wouldn't be too hard to extend this to combinations of modifiers.

cesium/packages/engine/Source/Core/ScreenSpaceEventHandler.js

Lines 25 to 43 in 85fb125

	function getInputEventKey(type, modifier) {
	let key = type;
	if (defined(modifier)) {
	key += `+${modifier}`;
	}
	return key;
	}
	function getModifier(event) {
	if (event.shiftKey) {
	return KeyboardEventModifier.SHIFT;
	} else if (event.ctrlKey) {
	return KeyboardEventModifier.CTRL;
	} else if (event.altKey) {
	return KeyboardEventModifier.ALT;
	}
	return undefined;
	}

We'd be happy to review a PR if you're willing to contribute! Please check out our contributing guide if you're interested

[Bob-vdV]

Alright, I will give it a go

[Bob-vdV]

@jjspace I opened a pull request with a simple implementation based on your suggestion