Hello3DMCP Server

Instructions

Implementation Reference

• server.js:1710-1757 (registration)

  Registration of the 'get_camera_distance' tool with the MCP server, including title, description, input schema, and handler function

  mcpServer.registerTool(
    'get_camera_distance',
    {
      title: 'Get Camera Distance',
      description: 'Get the current camera distance from origin (dolly position). ' +
        'Query this before relative distance changes to ensure accuracy. ' +
        'For absolute changes, you may use recently queried state from context if no manual interactions occurred.',
      inputSchema: {}
    },
    async () => {
      const sessionId = getCurrentSessionId();
      if (!sessionId) {
        return {
          content: [
            {
              type: 'text',
              text: 'Error: No active session found.'
            }
          ],
          isError: true
        };
      }
  
      try {
        const { state, metadata } = await getState(sessionId);
        const distance = state.camera?.distance ?? 0;
        
        return {
          content: [
            {
              type: 'text',
              text: formatStateResponse(distance.toString(), 'Camera distance', sessionId, metadata)
            }
          ]
        };
      } catch (error) {
        return {
          content: [
            {
              type: 'text',
              text: `Error retrieving camera distance: ${error.message}`
            }
          ],
          isError: true
        };
      }
    }
  );

• server.js:1719-1756 (handler)

  Handler function for get_camera_distance tool - retrieves current camera distance from browser state via WebSocket communication and returns formatted response with metadata

  async () => {
    const sessionId = getCurrentSessionId();
    if (!sessionId) {
      return {
        content: [
          {
            type: 'text',
            text: 'Error: No active session found.'
          }
        ],
        isError: true
      };
    }
  
    try {
      const { state, metadata } = await getState(sessionId);
      const distance = state.camera?.distance ?? 0;
      
      return {
        content: [
          {
            type: 'text',
            text: formatStateResponse(distance.toString(), 'Camera distance', sessionId, metadata)
          }
        ]
      };
    } catch (error) {
      return {
        content: [
          {
            type: 'text',
            text: `Error retrieving camera distance: ${error.message}`
          }
        ],
        isError: true
      };
    }
  }

• server.js:284-316 (helper)

  Helper function getState() - queries state from browser via WebSocket with timeout handling, returns state with metadata (source, timestamp, cache status)

  async function getState(sessionId) {
    let state;
    let source;
    let wasCached = false;
    
    // Always query browser for current state
    try {
      state = await queryStateFromBrowser(sessionId);
      source = 'fresh';
    } catch (error) {
      // If query fails, fall back to cache if available (browser may be disconnected)
      const cached = sessionStateCache.get(sessionId);
      if (cached) {
        console.warn(`Browser query failed for session ${sessionId}, returning cached state: ${error.message}`);
        state = cached.state;
        source = 'cache';
        wasCached = true;
      } else {
        // No cache available, throw error
        throw new Error(`Unable to retrieve state: ${error.message}. Browser may be disconnected.`);
      }
    }
    
    // Return state with metadata
    return {
      state,
      metadata: {
        source,
        wasCached,
        timestamp: new Date().toISOString()
      }
    };
  }

• server.js:319-327 (helper)

  Helper function formatStateResponse() - formats state query responses with property name, session ID, and metadata including staleness warnings

  function formatStateResponse(value, propertyName, sessionId, metadata) {
    const timestamp = metadata.timestamp;
    const source = metadata.source;
    const stalenessWarning = metadata.wasCached 
      ? ' (using cached state - browser may be disconnected)' 
      : '';
    
    return `${propertyName}: ${value} (queried at ${timestamp}, source: ${source}${stalenessWarning})`;
  }

• server.js:2882-2888 (helper)

  Helper function getCurrentSessionId() - retrieves the current session ID from either STDIO mode or HTTP mode context

  function getCurrentSessionId() {
    if (isStdioMode) {
      return STDIO_SESSION_ID;
    } else {
      return sessionContext.getStore();
    }
  }