C++开源库dxflib解析DXF文件实战
好的，我们来详细探讨一下 dxflib 这个专门用于处理 DXF (Drawing Exchange Format) 文件的 C++ 开源库。
一、dxflib 简介
dxflib 是一个轻量级、纯 C++ 编写的开源库，其主要功能是 解析和生成 AutoCAD DXF 文件。DXF 文件是 AutoCAD 软件用于在不同 CAD 系统之间交换图形数据的标准格式。
核心特点
- 轻量级： 代码量相对较小，易于集成到项目中。
- 纯 C++： 不依赖外部库（如 Qt），便于跨平台使用。
- 面向对象： 采用继承和虚函数机制，用户通过继承特定的接口类并实现虚函数来处理解析到的 DXF 实体和表记录。
- 支持版本： 主要支持较新版本的 DXF 格式（如 AutoCAD 2000 及以后版本使用的格式），对 R12/R13 等旧版本的支持可能有限或不完整。
- 功能聚焦： 专注于 DXF 文件的读（解析）和写（生成），不提供图形显示功能。
二、核心概念与工作机制
1. 解析 (Reading)
解析 DXF 文件的核心类是 dl_dxf。其工作流程如下：
- 创建解析器：
dl_dxf dxf; - 设置回调接口： 用户需要创建一个类，继承自
dl_creationadapter（或实现其定义的接口），并重写感兴趣的虚函数。这些函数在解析器遇到对应的 DXF 结构时会被调用。class MyDXFReader : public DL_CreationAdapter { public: void addLine(const DL_LineData& data) override { // 处理解析到的直线实体 std::cout << "Line: (" << data.x1 << ", " << data.y1 << ") to (" << data.x2 << ", " << data.y2 << ") "; } void addCircle(const DL_CircleData& data) override { // 处理解析到的圆实体 } void addLayer(const DL_LayerData& data) override { // 处理解析到的图层记录 } // ... 实现其他感兴趣的函数： addArc, addPoint, addText, addBlock, etc. };http://my.tv.sohu.com/us/442300932/699357699.shtml
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- 关联适配器： 将自定义的适配器对象设置给解析器。
MyDXFReader myAdapter; dxf.setCallback(&myAdapter); - 执行解析： 调用
dl_dxf::in(...)方法，传入文件名和编码（如果需要）。dxf.in("example.dxf", "CP1252"); // 假设文件使用 Windows-1252 编码
解析器会逐行读取 DXF 文件，当遇到 SECTION, ENDSEC, TABLE, ENDTAB, BLOCK, ENDBLK, ENTITY 等关键标记，以及具体的实体数据（如 LINE, CIRCLE, LAYER）时，会调用适配器类中对应的虚函数，并传递相关的数据结构（如 DL_LineData, DL_CircleData, DL_LayerData）。用户在这些函数中实现对解析数据的处理逻辑。
2. 生成 (Writing)
生成 DXF 文件的核心类也是 dl_dxf。其工作流程如下：
- 创建生成器：
dl_dxf dxf; - 打开文件输出流： 通常使用
std::ofstream。std::ofstream outfile("output.dxf"); if (!outfile.is_open()) { // 处理错误 return; } - 写入文件头：
dxf.writeHeader(outfile); // 可以在这里设置一些全局变量（如果库支持且需要） - 写入表区域： 定义图层、线型、文本样式、视图等。
dxf.writeTables(outfile); // 写入图层表 dxf.tableLayers(outfile, 1); // 1 表示图层表的记录数 DL_LayerData myLayer("MyLayer", DL_Flags::Flag0); // 创建图层数据 dxf.writeLayer(outfile, myLayer); // 写入一个图层记录 // ... 写入其他表记录（线型、文本样式等）http://my.tv.sohu.com/us/442300932/699357699.shtml
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https://tv.sohu.com/v/dXMvNDQyMzAwOTMyLzY5OTM1ODgzMy5zaHRtbA==.html
http://my.tv.sohu.com/us/442300932/699359137.shtml
https://tv.sohu.com/v/dXMvNDQyMzAwOTMyLzY5OTM1OTEzNy5zaHRtbA==.html
- 写入块区域： (可选) 如果需要定义块。
dxf.writeBlocks(outfile); // ... 写入块定义 - 写入实体区域： 绘制实际的图形对象。
dxf.writeEntities(outfile); // 设置当前属性（图层、颜色、线型等），通常通过写组码实现 dxf.writeAttribute(outfile); // 可能需要根据库的具体 API 调整 // 写入一个直线实体 DL_LineData lineData(0.0, 0.0, 0.0, // start point (x, y, z) 100.0, 100.0, 0.0); // end point (x, y, z) dxf.writeLine(outfile, lineData); // 写入一个圆实体 DL_CircleData circleData(50.0, 50.0, 0.0, // center (x, y, z) 25.0); // radius dxf.writeCircle(outfile, circleData); // ... 写入其他实体（圆弧、多段线、文本、点等） - 写入文件尾：
dxf.writeObjects(outfile); // 通常用于存储非图形对象（可选） dxf.writeEOF(outfile); // 写入文件结束标记 - 关闭文件：
outfile.close();
生成过程本质上是按照 DXF 文件的结构规范（HEADER, TABLES, BLOCKS, ENTITIES, OBJECTS, EOF），使用 dl_dxf 提供的 writeHeader, writeTables, writeLayer, writeLine, writeCircle 等方法向输出流写入相应的组码和数据。
三、实战示例：读取并打印简单 DXF 文件中的直线
#include
#include
#include
#include
// 自定义适配器类，继承 dl_creationadapter
class SimpleDXFReader : public DL_CreationAdapter {
public:
// 当解析到直线时调用
void addLine(const DL_LineData& data) override {
std::cout << "Found Line:" << std::endl;
std::cout << " Start: (" << data.x1 << ", " << data.y1 << ", " << data.z1 << ")" << std::endl;
std::cout << " End: (" << data.x2 << ", " << data.y2 << ", " << data.z2 << ")" << std::endl;
}
// 可以省略其他不关心的虚函数实现（如 addCircle, addLayer 等）
// 但必须实现所有纯虚函数，如果基类有的话。通常 dl_creationadapter 提供了默认实现（空函数）。
};
int main() {
// 1. 创建 DXF 解析器
DL_Dxf dxf;
// 2. 创建自定义适配器实例
SimpleDXFReader adapter;
// 3. 将适配器设置给解析器
dxf.setCallback(&adapter);
// 4. 尝试解析文件
const char* filename = "sample.dxf"; // 替换为你的 DXF 文件路径
bool success = dxf.in(filename, "CP1252"); // 使用 Windows-1252 编码（常见于英文版AutoCAD生成的DXF）
if (!success) {
std::cerr << "Failed to parse DXF file: " << filename << std::endl;
return 1;
}
std::cout << "DXF file parsed successfully." << std::endl;
return 0;
}
四、实战示例：生成一个包含直线和圆的简单 DXF 文件
#include
#include
#include // 通常 dxflib 使用这个来写 ASCII DXF
int main() {
// 1. 创建 DXF 生成器
DL_Dxf dxf;
// 2. 打开输出文件流
std::ofstream outfile("output.dxf");
if (!outfile.is_open()) {
std::cerr << "Failed to create output file." << std::endl;
return 1;
}
// 3. 创建 DXF 写入器 (通常使用 ASCII 格式)
DL_WriterA writer(outfile); // 将输出流关联到写入器
dxf.writeHeader(writer); // 写入文件头
writer.writeString(9, "$ACADVER"); // 设置版本为 AC1018 (AutoCAD 2004-2006)
writer.writeString(1, "AC1018");
writer.writeString(9, "$INSBASE"); // 设置插入基点 (0,0,0)
writer.writeReal(10, 0.0);
writer.writeReal(20, 0.0);
writer.writeReal(30, 0.0);
// ... 可以设置更多头变量
// 4. 写入表区域
dxf.writeTables(writer);
// 4.1 写入图层表 (1 个图层)
dxf.tableLayers(writer, 1);
// 创建一个名为 "0" 的图层 (默认层)
DL_LayerData layerData("0", DL_Flags::Flag0); // DL_Flags::Flag0 通常表示默认状态
dxf.writeLayer(writer, layerData);
// 5. 写入实体区域
dxf.writeEntities(writer);
// 5.1 设置当前属性为图层 "0"
writer.writeString(0, "LAYER"); // 实体属性设置通常直接写组码
writer.writeString(8, "0"); // 组码 8 表示图层名
// 5.2 写入一条直线 (从 (0,0,0) 到 (100,100,0))
DL_LineData lineData(0.0, 0.0, 0.0, 100.0, 100.0, 0.0);
dxf.writeLine(writer, lineData);
// 5.3 写入一个圆 (圆心 (50,50,0), 半径 25)
DL_CircleData circleData(50.0, 50.0, 0.0, 25.0);
dxf.writeCircle(writer, circleData);
// 6. 写入文件尾
dxf.writeObjects(writer); // 非图形对象 (可选)
dxf.writeEOF(writer); // 文件结束标记
// 7. 关闭文件
outfile.close();
std::cout << "DXF file 'output.dxf' generated successfully." << std::endl;
return 0;
}
五、注意事项
- 文档： dxflib 的官方文档可能相对简单，深入使用时需要参考其源代码（特别是
dl_creationadapter.h和dl_dxf.h）和 DXF 格式规范。 - 版本兼容性： 明确你的 DXF 文件版本，并确认 dxflib 是否支持其所有特性。生成时注意设置正确的
$ACADVER头变量。 - 错误处理： 在
dl_dxf::in(...)中检查返回值。解析复杂的 DXF 文件时，自定义适配器需要考虑错误处理和意外数据。 - 内存管理： 解析器在调用回调函数传递数据后，通常不会保留数据。用户需要在适配器中妥善存储或处理接收到的数据。
- 坐标系： DXF 通常使用右手坐标系。注意数据的单位（如毫米、英寸）。
- 组码： 对于生成操作，有时需要直接写入特定的组码来设置属性（如颜色、线型、图层）。熟悉 DXF 组码含义很有帮助。
通过继承 dl_creationadapter 并实现其虚函数，你可以灵活地处理 DXF 文件中的各种实体和表记录。使用 dl_dxf 的 write* 系列函数，你可以按照结构要求生成有效的 DXF 文件。
