取景距离抬到不会让轨道缩放范围颠倒的下限

- packages/model3d-viewer/src/framing.ts：computeModel3dViewerFitDistance 对调用方传入的距离加下限（radius × 0.2 / 8），避免 distance 过小时 maxDistance 小于 minDistance，取景与轨道钳制同时失效
- packages/model3d-viewer/src/framing.test.ts：补极小距离的下限用例

packages/model3d-viewer/src/framing.test.ts

@@ -143,6 +143,20 @@ describe('computeModel3dViewerFitDistance', () => {
 
     expect(distance).toBe(7);
   });
+
+  it('传入的距离小到会让缩放范围颠倒时，抬到能站住的下限', () => {
+    const framing = computeModel3dViewerFraming({
+      box: CUBE,
+      aspect: 1,
+      distance: computeModel3dViewerFitDistance({
+        box: CUBE,
+        aspect: 1,
+        distance: 0.001,
+      }),
+    });
+
+    expect(framing.maxDistance).toBeGreaterThanOrEqual(framing.minDistance);
+  });
 });
 
 describe('createModel3dViewerFitSolver', () => {

packages/model3d-viewer/src/framing.ts

@@ -218,7 +218,13 @@ export function computeModel3dViewerFitDistance(
   // 会让 maxDistance 小于 minDistance，取景与轨道钳制一起失效，故按无效处理。
   const distance = input.distance;
   if (distance !== undefined && Number.isFinite(distance) && distance > 0) {
-    return distance;
+    // `computeModel3dViewerFraming` 由这个距离推出 maxDistance = distance × 8、minDistance
+    // = radius × 0.2；距离小到 0.025 × radius 以下时两者会颠倒，取景与轨道钳制一起失效。
+    return Math.max(
+      distance,
+      (computeModel3dViewerBoxRadius(input.box) * MIN_DISTANCE_RATIO) /
+        MAX_DISTANCE_RATIO,
+    );
   }
   const solver = createModel3dViewerFitSolver({
     center: computeModel3dViewerBoxCenter(input.box),