Allow speed providers to disable Drag Ruler on a per-token basis (resolves #24)

src/api.js

@@ -12,6 +12,7 @@ function register(module, type, speedProvider) {
 	}
 	else {
 		speedProvider.id = id
+		speedProvider.usesRuler = () => true
 		providerInstance = speedProvider
 	}
 	setupProvider(providerInstance)

src/main.js

@@ -1,6 +1,6 @@
 "use strict"
 
-import {getRangesFromSpeedProvider, getUnreachableColorFromSpeedProvider, initApi, registerModule, registerSystem} from "./api.js"
+import {currentSpeedProvider, getRangesFromSpeedProvider, getUnreachableColorFromSpeedProvider, initApi, registerModule, registerSystem} from "./api.js"
 import {getHexSizeSupportTokenGridCenter} from "./compatibility.js"
 import {measure, moveTokens, onMouseMove} from "./foundry_imports.js"
 import {performMigrations} from "./migration.js"
@@ -142,6 +142,8 @@ function onKeyShift(up) {
 }
 
 function onTokenLeftDragStart(event) {
+	if (!currentSpeedProvider.usesRuler(this))
+		return
 	const ruler = canvas.controls.ruler
 	ruler.draggedToken = this
 	let tokenCenter

src/speed_provider.js

@@ -73,6 +73,16 @@ export class SpeedProvider {
 		}
 	}
 
+	/**
+	 * Returns a boolean indicating whether this token will use a Ruler or not.
+	 * If this is returns `false` for a token Drag Ruler will be disabled for that token. Dragging a token for which this function
+	 * returns false will behave as if Drag Ruler wasn't installed.
+	 * If usesRuler returns `false` it's guranteed that the `getRanges` function won't be called for that token.
+	 */
+	usesRuler(token) {
+		return true
+	}
+
 	/**
 	 * Constructs a new instance of he speed provider
 	 *