Add support for difficult terrain via Terrain Ruler module (resolves #1)

src/compatibility.js

@@ -1,3 +1,6 @@
+import {getPixelsFromGridPosition} from "./foundry_fixes.js"
+import {getColorForDistance} from "./main.js"
+
 export function getHexSizeSupportTokenGridCenter(token) {
 	const tokenCenterOffset = CONFIG.hexSizeSupport.getCenterOffset(token)
 	const tokenCenter = {x: token.x + tokenCenterOffset.x, y: token.y + tokenCenterOffset.y}
@@ -17,3 +20,11 @@ export function getHexSizeSupportTokenGridCenter(token) {
 	}
 	return tokenCenter
 }
+
+export function highlightMeasurementTerrainRuler(ray, startDistance) {
+	for (const space of ray.terrainRulerVisitedSpaces) {
+		const [x, y] = getPixelsFromGridPosition(space.x, space.y);
+		const color = getColorForDistance.call(this, startDistance, space.distance)
+		canvas.grid.highlightPosition(this.name, {x, y, color: color})
+	}
+}

src/foundry_fixes.js

@@ -0,0 +1,21 @@
+// Wrapper to fix a FoundryVTT bug that causes the return values of canvas.grid.grid.getPixelsFromGridPosition to be ordered inconsistently
+
+// https://gitlab.com/foundrynet/foundryvtt/-/issues/4705
+export function getPixelsFromGridPosition(xGrid, yGrid) {
+	if (canvas.grid.isHex) {
+		return canvas.grid.grid.getPixelsFromGridPosition(yGrid, xGrid)
+	}
+	const [x, y] = canvas.grid.grid.getPixelsFromGridPosition(xGrid, yGrid)
+	if (canvas.grid.type === CONST.GRID_TYPES.SQUARE)
+		return [y, x]
+	return [x, y]
+}
+
+// Wrapper to fix a FoundryVTT bug that causes the return values of canvas.grid.grid.getPixelsFromGridPosition to be ordered inconsistently
+// https://gitlab.com/foundrynet/foundryvtt/-/issues/4705
+export function getGridPositionFromPixels(xPixel, yPixel) {
+	const [x, y] = canvas.grid.grid.getGridPositionFromPixels(xPixel, yPixel)
+	if (canvas.grid.type !== CONST.GRID_TYPES.GRIDLESS)
+		return [y, x]
+	return [x, y]
+}

src/foundry_imports.js

@@ -1,4 +1,6 @@
+import {highlightMeasurementTerrainRuler} from "./compatibility.js";
 import {getColorForDistance} from "./main.js"
+import {zip} from "./util.js"
 
 // This is a modified version of Ruler.moveToken from foundry 0.7.9
 export async function moveTokens(draggedToken, selectedTokens) {
@@ -127,7 +129,13 @@ export function measure(destination, {gridSpaces=true, snap=false} = {}) {
 	}
 
 	// Compute measured distance
-	const distances = canvas.grid.measureDistances(centeredSegments, { gridSpaces });
+	const terrainRulerAvailable = game.modules.get("terrain-ruler")?.active && canvas.grid.type !== CONST.GRID_TYPES.GRIDLESS
+	let distances
+	if (terrainRulerAvailable)
+		distances = game.terrainRuler.measureDistances(centeredSegments)
+	else
+		distances = canvas.grid.measureDistances(centeredSegments, { gridSpaces });
+
 	let totalDistance = 0;
 	for (let [i, d] of distances.entries()) {
 		let s = segments[i];
@@ -149,7 +157,7 @@ export function measure(destination, {gridSpaces=true, snap=false} = {}) {
 		rulerColor = getColorForDistance.call(this, totalDistance)
 	else
 		rulerColor = this.color
-	for (let s of segments) {
+	for (const [s, cs] of zip(segments, centeredSegments)) {
 		const { ray, label, text, last } = s;
 
 		// Draw line segment
@@ -166,7 +174,10 @@ export function measure(destination, {gridSpaces=true, snap=false} = {}) {
 		}
 
 		// Highlight grid positions
-		highlightMeasurementNative.call(this, ray, s.startDistance);
+		if (terrainRulerAvailable)
+			highlightMeasurementTerrainRuler.call(this, cs.ray, s.startDistance)
+		else
+			highlightMeasurementNative.call(this, ray, s.startDistance);
 	}
 
 	// Draw endpoints

src/util.js

@@ -0,0 +1,5 @@
+export function* zip(it1, it2) {
+	for (let i = 0;i < Math.min(it1.length, it2.length);i++) {
+		yield [it1[i], it2[i]]
+	}
+}