fix(Entities): Invalidate matrix cache when setting a world matrix (#874

)

src/core/Entity.js

@@ -456,6 +456,12 @@ export class Entity {
 		this.rot = rot;
 		this.scale = scale;
 		this._localMatrixDirty = false;
+
+		// Mat4.decompose() doesn't extract negative scales correctly right now.
+		// Because of this, it's possible for the world matrix of children not
+		// to get marked as dirty when the scale changes from -1,-1,-1 to 1,1,1 for example.
+		// To fix that, we manually mark them as dirty.
+		this._markWorldMatrixDirty();
 	}
 
 	get worldMatrix() {
@@ -469,10 +475,12 @@ export class Entity {
 
 	_onWorldMatrixChange() {
 		if (this._ignoreWorldMatrixChanges) return;
-		const {pos, rot, scale} = this._worldMatrix.decompose();
-		this._worldPos.set(pos);
-		this._worldRot.set(rot);
-		this._worldScale.set(scale);
+		if (!this.parent) {
+			this.localMatrix.set(this._worldMatrix);
+		} else {
+			const newLocalMatrix = this.parent.worldMatrix.clone().invert().multiplyMatrix(this._worldMatrix);
+			this.localMatrix.set(newLocalMatrix);
+		}
 	}
 
 	/**

test/unit/src/core/Entity/transformations.test.js

@@ -636,6 +636,72 @@ Deno.test({
 	},
 });
 
+Deno.test({
+	name: "setting world matrix affects children",
+	fn() {
+		const root = new Entity("root");
+		const childA = root.add(new Entity("A")); // The entity we will be moving up
+		const childB = childA.add(new Entity("B")); // The entity we will reset (i.e. move down again)
+		const childC = childB.add(new Entity("C")); // The entity that should have the identity matrix
+
+		childA.worldMatrix.set(Mat4.createTranslation(0, 1, 0));
+		assertMatAlmostEquals(childB.worldMatrix, Mat4.createTranslation(0, 1, 0));
+		assertMatAlmostEquals(childC.worldMatrix, Mat4.createTranslation(0, 1, 0));
+
+		childB.worldMatrix.set(new Mat4());
+		assertMatAlmostEquals(childC.worldMatrix, new Mat4());
+	},
+});
+
+Deno.test({
+	name: "setting world matrix affects children when scaling negatively",
+	fn() {
+		// At the time of writing, decomposing negatively scaled matrices means the sign is lost.
+		// So Mat4.createScale(-1, 1, 1) and Mat4.createScale(1, 1, 1) both return a scale of (1,1,1) when calling decompose()
+		// As a result changing the scale of a Entity.worldMatrix doesn't cause the worldmatrices
+		// of children to get marked as dirty.
+		const root = new Entity("root");
+		const childA = root.add(new Entity("A")); // The entity we will be moving up
+		const childB = childA.add(new Entity("B")); // The entity we will reset (i.e. move down again)
+
+		childA.worldMatrix.set(Mat4.createScale(-1, 1, 1));
+		assertMatAlmostEquals(childB.worldMatrix, Mat4.createScale(-1, 1, 1));
+
+		childA.worldMatrix.set(new Mat4());
+		assertMatAlmostEquals(childB.worldMatrix, new Mat4());
+	},
+});
+
+Deno.test({
+	name: "setting world matrix affects local position",
+	fn() {
+		const root = new Entity("root");
+		const childA = root.add(new Entity("A")); // The entity we will be moving up
+		const childB = childA.add(new Entity("B")); // The entity we will reset (i.e. move down again)
+
+		childA.worldMatrix.set(Mat4.createTranslation(0, 1, 0));
+		assertVecAlmostEquals(childB.pos, [0, 0, 0]);
+
+		childB.worldMatrix.set(new Mat4());
+		assertVecAlmostEquals(childB.pos, [0, -1, 0]);
+	},
+});
+
+Deno.test({
+	name: "setting world matrix affects world position",
+	fn() {
+		const root = new Entity("root");
+		const childA = root.add(new Entity("A")); // The entity we will be moving up
+		const childB = childA.add(new Entity("B")); // The entity we will reset (i.e. move down again)
+
+		childA.worldMatrix.set(Mat4.createTranslation(0, 1, 0));
+		assertVecAlmostEquals(childB.worldPos, [0, 1, 0]);
+
+		childB.worldMatrix.set(new Mat4());
+		assertVecAlmostEquals(childB.worldPos, [0, 0, 0]);
+	},
+});
+
 Deno.test({
 	name: "Issue #203: Changing parent transformation shouldn't adjust local transformation from children",
 	fn() {