如何为Autodesk Viewer实现PDF按标准纸型缩放的扩展功能

要实现PDF缩放到指定纸型的逻辑，核心是获取当前PDF图纸的原始尺寸、计算适配目标纸型的缩放因子，并调整Viewer相机让图纸匹配目标尺寸显示。以下是完整实现方案：

关键说明 #

• Autodesk Viewer中PDF图纸的尺寸单位为英寸，需先将毫米单位的纸型尺寸转换为英寸（1英寸 = 25.4毫米）
• 需确保PDF图纸已完全加载，避免获取尺寸时出现空值
• 保持PDF宽高比，避免拉伸变形

修改后的完整扩展代码 #

替换原扩展中的scalePdfToSize、load、unload方法，补充必要逻辑：

// *******************************************
// PDF Scaling Extension
// *******************************************
class PdfScalingExtension extends Autodesk.Viewing.Extension {
  constructor(viewer, options) {
    super(viewer, options);
    this.paperSizes = {
      A0: { width: 841, height: 1189, text: "A0 - 841mm x 1189mm" },
      A1: { width: 594, height: 841, text: "A1 - 594mm x 841mm" },
      A2: { width: 420, height: 594, text: "A2 - 420mm x 594mm" },
      A3: { width: 297, height: 420, text: "A3 - 297mm x 420mm" },
      A4: { width: 210, height: 297, text: "A4 - 210mm x 297mm" },
      A5: { width: 148, height: 210, text: "A5 - 148mm x 210mm" },
      A6: { width: 105, height: 148, text: "A6 - 105mm x 148mm" },
      A7: { width: 74, height: 105, text: "A7 - 74mm x 105mm" },
      A8: { width: 52, height: 74, text: "A8 - 52mm x 74mm" },
      A9: { width: 37, height: 52, text: "A9 - 37mm x 52mm" },
      A10: { width: 26, height: 37, text: "A10 - 26mm x 37mm" },
    };
    // 存储事件监听句柄，用于卸载时清理
    this.onGeometryLoaded = () => {
      if (this.viewer.model.is2D()) {
        console.log("PDF图纸已加载完成，可进行缩放操作");
      }
    };
  }

  async load() {
    // 监听模型加载完成事件，确保能获取到图纸信息
    this.viewer.addEventListener(Autodesk.Viewing.GEOMETRY_LOADED_EVENT, this.onGeometryLoaded);
    return true;
  }

  unload() {
    // 移除事件监听和工具栏控件，避免内存泄漏
    this.viewer.removeEventListener(Autodesk.Viewing.GEOMETRY_LOADED_EVENT, this.onGeometryLoaded);
    if (this._group) {
      this.viewer.toolbar.removeControl(this._group);
      this._group = null;
    }
    return true;
  }

  onToolbarCreated() {
    // Create a new toolbar group
    this._group = this.viewer.toolbar.getControl("PdfScalingExtensionsToolbar");
    if (!this._group) {
      this._group = new Autodesk.Viewing.UI.ControlGroup("PdfScalingExtensionsToolbar");
      this.viewer.toolbar.addControl(this._group);
    }

    // Paper Size Dropdown
    let paperSizeDropdown = new Autodesk.Viewing.UI.ComboButton("PaperSizeDropdown");
    paperSizeDropdown.setToolTip("Select Paper Size");
    paperSizeDropdown.icon.classList.add("fas", "fa-file-alt");
    paperSizeDropdown.container.style.color = "white"; // Set the color of dropdown text to white
    this._group.addControl(paperSizeDropdown);

    // Add paper size options to dropdown
    for (let size in this.paperSizes) {
      let option = new Autodesk.Viewing.UI.Button(size);
      option.setToolTip(this.paperSizes[size].text);
      option.text = this.paperSizes[size].text; // Set the text of the button to the paper size name
      option.onClick = (ev) => {
        this.scalePdfToSize(this.paperSizes[size]);
      };
      paperSizeDropdown.addControl(option);
    }
  }

  scalePdfToSize(size) {
    // 校验当前是否为2D PDF图纸
    if (!this.viewer.model || !this.viewer.model.is2D()) {
      console.warn("当前不是2D PDF图纸，无法执行缩放操作");
      return;
    }

    // 1. 将目标纸型尺寸从毫米转换为Viewer内部使用的英寸单位
    const targetWidthIn = size.width / 25.4;
    const targetHeightIn = size.height / 25.4;

    // 2. 获取当前PDF图纸的原始尺寸（单位：英寸）
    const sheet = this.viewer.model.getSheet();
    if (!sheet) {
      console.warn("无法获取当前图纸信息，请确保图纸已加载完成");
      return;
    }
    const originalWidth = sheet.width;
    const originalHeight = sheet.height;

    // 3. 计算适配缩放因子（取宽高比例的最小值，避免图纸超出目标纸型范围）
    const scaleX = targetWidthIn / originalWidth;
    const scaleY = targetHeightIn / originalHeight;
    const scaleFactor = Math.min(scaleX, scaleY);

    // 4. 计算目标视图范围，基于原始尺寸和缩放因子
    const targetBounds = new THREE.Box3(
      new THREE.Vector3(0, 0, 0),
      new THREE.Vector3(originalWidth * scaleFactor, originalHeight * scaleFactor, 0)
    );

    // 5. 调整相机适配目标范围，保持图纸居中显示
    this.viewer.navigation.fitBounds(true, targetBounds);

    console.log(`已缩放PDF至目标纸型: ${size.width}mm x ${size.height}mm，缩放因子: ${scaleFactor.toFixed(4)}`);
  }
}

Autodesk.Viewing.theExtensionManager.registerExtension("PdfScalingExtension", PdfScalingExtension);

逻辑说明 #

1. 单位转换：将纸型的毫米尺寸转为Viewer内部使用的英寸单位，确保计算精度
2. 图纸尺寸获取：通过model.getSheet()获取当前PDF的原始尺寸
3. 缩放因子计算：取宽、高方向缩放比例的最小值，保证图纸完整适配目标纸型且不变形
4. 相机适配：调用navigation.fitBounds()让Viewer自动调整相机，将图纸缩放到目标范围并居中显示

内容的提问来源于stack exchange，提问作者Vibhav Joshi