Model centering can be off on Unified mode (#193)

Fixes #182

src/components/diff/BaseModel.tsx

@@ -1,17 +1,17 @@
 import { useThree } from '@react-three/fiber'
 import type { MutableRefObject, PropsWithChildren } from 'react'
 import { Suspense, useEffect, useRef } from 'react'
-import { BufferGeometry } from 'three'
+import { Sphere } from 'three'
 import { Vector3 } from 'three'
 import { calculateFovFactor } from './Camera'
 
 type BaseModelProps = {
     cameraRef: MutableRefObject<any>
-    geometry: BufferGeometry
+    boundingSphere: Sphere | null | undefined
 }
 
 export function BaseModel({
-    geometry,
+    boundingSphere,
     cameraRef,
     children,
 }: PropsWithChildren<BaseModelProps>) {
@@ -21,14 +21,9 @@ export function BaseModel({
 
     // Camera view, adapted from KittyCAD/website
     useEffect(() => {
-        if (geometry && cameraRef.current) {
-            geometry.computeBoundingSphere()
-            // TODO: understand the implications of this,
-            // it's been disabled as it was causing before and after to be misaligned
-            // geometry.center()
-
+        if (boundingSphere && cameraRef.current) {
             // move the camera away so the object fits in the view
-            const { radius } = geometry.boundingSphere || { radius: 1 }
+            const { radius } = boundingSphere || { radius: 1 }
             if (!camera.position.length()) {
                 const arbitraryNonZeroStartPosition = new Vector3(0.5, 0.5, 1)
                 camera.position.copy(arbitraryNonZeroStartPosition)
@@ -42,7 +37,7 @@ export function BaseModel({
             camera.zoom = fovFactor / camera.position.length()
             camera.updateProjectionMatrix()
         }
-    }, [geometry, camera, cameraRef, canvasHeight])
+    }, [boundingSphere, camera, cameraRef, canvasHeight])
 
     return (
         <Suspense fallback={null}>

src/components/diff/CadDiff.tsx

@@ -26,6 +26,7 @@ function loadGeometry(file: string, checkUV = false): BufferGeometry {
             new BufferAttribute(new Float32Array([]), 1)
         )
     }
+    geometry.computeBoundingSphere() // will be used for auto-centering
     return geometry
 }
 

src/components/diff/UnifiedModel.tsx

@@ -1,6 +1,14 @@
 import type { MutableRefObject } from 'react'
 import { useTheme } from '@primer/react'
-import { BufferGeometry } from 'three'
+import {
+    Box3,
+    BufferGeometry,
+    Group,
+    Mesh,
+    MeshBasicMaterial,
+    Sphere,
+    Vector3,
+} from 'three'
 import { Geometry, Base, Subtraction, Intersection } from '@react-three/csg'
 import { BaseModel } from './BaseModel'
 
@@ -13,6 +21,20 @@ type UnifiedModelProps = {
     showDeletions: boolean
 }
 
+function getCommonSphere(
+    beforeGeometry: BufferGeometry,
+    afterGeometry: BufferGeometry
+) {
+    const group = new Group()
+    const dummyMaterial = new MeshBasicMaterial()
+    group.add(new Mesh(beforeGeometry, dummyMaterial))
+    group.add(new Mesh(afterGeometry, dummyMaterial))
+    const boundingBox = new Box3().setFromObject(group)
+    const center = new Vector3()
+    boundingBox.getCenter(center)
+    return boundingBox.getBoundingSphere(new Sphere(center))
+}
+
 export function UnifiedModel({
     beforeGeometry,
     afterGeometry,
@@ -27,9 +49,10 @@ export function UnifiedModel({
     const deletionsColor = theme?.colors.danger.muted
 
     return (
-        // TODO: here we give beforeGeometry for auto camera centering,
-        // for the lack of something better. Need to check the implications
-        <BaseModel geometry={beforeGeometry} cameraRef={cameraRef}>
+        <BaseModel
+            boundingSphere={getCommonSphere(beforeGeometry, afterGeometry)}
+            cameraRef={cameraRef}
+        >
             {/* Unchanged */}
             <mesh>
                 <meshPhongMaterial

src/components/diff/WireframeModel.tsx

@@ -25,7 +25,7 @@ export function WireframeModel({ geometry, cameraRef, colors }: Props) {
     )
 
     return (
-        <BaseModel geometry={geometry} cameraRef={cameraRef}>
+        <BaseModel boundingSphere={geometry.boundingSphere} cameraRef={cameraRef}>
             <group ref={groupRef}>
                 <mesh
                     castShadow={true}