DWG文件预览图提取

cad/dwgthumbnail.cpp

@@ -0,0 +1,109 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <windows.h>
+
+bool thumbnail(const char *filePath, const char *savePath) {
+  FILE *fd = fopen(filePath, "rb");
+  if (fd == NULL) {
+    fprintf(stderr, "无法打开文件\n");
+    return false;
+  }
+
+  fseek(fd, 13, SEEK_SET);
+  unsigned int sentinel_pos;
+  fread(&sentinel_pos, sizeof(unsigned int), 1, fd);
+  printf("Hex: %X\n", sentinel_pos);
+
+  const int SIZE_SN = 39;
+
+  char buf[SIZE_SN] = {0};
+  unsigned char SN[] = {0x1F, 0x25, 0x6D, 0x07, 0xD4, 0x36, 0x28, 0x28,
+                        0x9D, 0x57, 0xCA, 0x3F, 0x9D, 0x44, 0x10, 0x2B};
+  fseek(fd, sentinel_pos, SEEK_SET);
+  fread(buf, SIZE_SN, 1, fd);
+
+  bool isdwg = true;
+  for (int i = 0; i != 16; i++) {
+    isdwg &= ((unsigned char)buf[i] == SN[i]);
+  }
+
+  if (isdwg && buf[20] == 2) {
+    for (int i = 0; i != sizeof(buf); i++)
+      printf("%0.2X ", buf[i] & 0xFF);
+  } else {
+    return false;
+  }
+
+  int data_size;
+  memcpy(&data_size, &buf[35], sizeof(int));
+
+  int pos;
+  memcpy(&pos, &buf[31], sizeof(int));
+
+  printf("\ndata_size: 0x%0.4X", data_size);
+  printf("\npos: 0x%0.4X\n", pos);
+
+  char *bmp_buf = new char[data_size];
+  memset(bmp_buf, 0, data_size);
+
+  fseek(fd, pos, SEEK_SET);
+  if (fread(bmp_buf, 1, data_size, fd) != data_size) {
+    fprintf(stderr, "读取失败\n");
+    delete[] bmp_buf;
+    fclose(fd);
+    return false;
+  }
+
+  FILE *bmp_file = fopen(savePath, "wb");
+  if (bmp_file == NULL) {
+    fprintf(stderr, "无法创建文件\n");
+    delete[] bmp_buf;
+    fclose(fd);
+    return false;
+  }
+  struct _BITMAP_HEADER {
+    char magic[2];
+    int file_size;
+    int reserved;
+    int offset;
+  } bmp_h;
+
+  /* Write bmp file header */
+  bmp_h.magic[0] = 'B';
+  bmp_h.magic[1] = 'M';
+  bmp_h.file_size = 14 + data_size; // file header + DIB data
+  bmp_h.reserved = 0;
+  bmp_h.offset = 14 + 40 + 4 * 256; // file header + DIB header + color table
+
+  // 写 BMP 文件头
+  fwrite(&bmp_h.magic[0], sizeof(char), 2, bmp_file);
+  fwrite(&bmp_h.file_size, 4, 3, bmp_file);
+
+  // 写bmp 图片数据
+  fwrite(bmp_buf, 1, data_size, bmp_file);
+
+  printf("\n --------->  thumbnail.bmp");
+
+  delete[] bmp_buf;
+  fclose(fd);
+  fclose(bmp_file);
+  return true;
+}
+
+int main(int argc, char *argv[]) {
+  const char *filePath = "example.dwg";
+  const char *savePath = "thumbnail.bmp";
+  if (2 == argc)
+    filePath = argv[1];
+
+  thumbnail(filePath, savePath);
+  return 0;
+}
+
+/*
+# 参考代码
+# https://github.com/LibreDWG/libredwg/blob/master/programs/dwgbmp.c
+# DWG文件的预览图像数据结构
+# https://blog.csdn.net/lzljy/article/details/103110823
+*/