First pass of load files through an interface (to allow loading from memory, zip file etc). So instead of posix fopen/fread, using CommonFileIOInterface.

A fileIO plugin can override custom file IO operations. As a small test, load files from a zipfile in memory.
Default fileIO implementation is in examples/Utils/b3BulletDefaultFileIO.h
Affects URDF, SDF, MJCF, Wavefront OBJ, STL, DAE, images.

examples/Utils/b3BulletDefaultFileIO.h

@@ -0,0 +1,175 @@
+
+#ifndef B3_BULLET_DEFAULT_FILE_IO_H
+#define B3_BULLET_DEFAULT_FILE_IO_H
+
+#include "../CommonInterfaces/CommonFileIOInterface.h"
+#include "b3ResourcePath.h"
+
+#include <stdio.h>
+#define B3_FILEIO_MAX_FILES 1024
+
+struct b3BulletDefaultFileIO : public CommonFileIOInterface
+{
+	static bool FileIOPluginFindFile(void* userPtr, const char* orgFileName, char* relativeFileName, int maxRelativeFileNameMaxLen)
+	{
+		b3BulletDefaultFileIO* fileIo = (b3BulletDefaultFileIO*) userPtr;
+		return fileIo->findFile(orgFileName, relativeFileName, maxRelativeFileNameMaxLen);
+	}
+
+	FILE* m_fileHandles[B3_FILEIO_MAX_FILES];
+	int m_numFileHandles;
+
+	b3BulletDefaultFileIO()
+		:m_numFileHandles(0)
+	{
+		for (int i=0;i<B3_FILEIO_MAX_FILES;i++)
+		{
+			m_fileHandles[i]=0;
+		}
+	}
+
+	virtual ~b3BulletDefaultFileIO()
+	{
+	}
+	virtual int fileOpen(const char* fileName, const char* mode)
+	{
+		//search a free slot
+		int slot = -1;
+		for (int i=0;i<B3_FILEIO_MAX_FILES;i++)
+		{
+			if (m_fileHandles[i]==0)
+			{
+				slot=i;
+				break;
+			}
+		}
+		if (slot>=0)
+		{
+			FILE*f = ::fopen(fileName, mode);
+			if (f)
+			{
+				m_fileHandles[slot]=f;
+			} else
+			{
+				slot=-1;
+			}
+		}
+		return slot;
+	}
+	virtual int fileRead(int fileHandle, char* destBuffer, int numBytes)
+	{
+		if (fileHandle>=0 && fileHandle < B3_FILEIO_MAX_FILES)
+		{
+			FILE* f = m_fileHandles[fileHandle];
+			if (f)
+			{
+				int readBytes = ::fread(destBuffer, 1, numBytes, f);
+				return readBytes;
+			}
+		}
+		return -1;
+			
+	}
+	virtual int fileWrite(int fileHandle,const char* sourceBuffer, int numBytes)
+	{
+		if (fileHandle>=0 && fileHandle < B3_FILEIO_MAX_FILES)
+		{
+			FILE* f = m_fileHandles[fileHandle];
+			if (f)
+			{
+				return ::fwrite(sourceBuffer, 1, numBytes,m_fileHandles[fileHandle]);
+			}
+		}
+		return -1;
+	}
+	virtual void fileClose(int fileHandle)
+	{
+		if (fileHandle>=0 && fileHandle < B3_FILEIO_MAX_FILES)
+		{
+			FILE* f = m_fileHandles[fileHandle];
+			if (f)
+			{
+				::fclose(f);
+				m_fileHandles[fileHandle]=0;
+			}
+		}
+	}
+
+	virtual bool findResourcePath(const char* fileName, char* relativeFileName, int relativeFileNameSizeInBytes)
+	{
+		return b3ResourcePath::findResourcePath(fileName, relativeFileName, relativeFileNameSizeInBytes, b3BulletDefaultFileIO::FileIOPluginFindFile, this);
+	}
+
+
+	virtual bool findFile(const char* orgFileName, char* relativeFileName, int maxRelativeFileNameMaxLen)
+	{
+		FILE* f = 0;
+		f = fopen(orgFileName, "rb");
+		if (f)
+		{
+			//printf("original file found: [%s]\n", orgFileName);
+			sprintf(relativeFileName, "%s", orgFileName);
+			fclose(f);
+			return true;
+		}
+
+		//printf("Trying various directories, relative to current working directory\n");
+		const char* prefix[] = {"./", "./data/", "../data/", "../../data/", "../../../data/", "../../../../data/"};
+		int numPrefixes = sizeof(prefix) / sizeof(const char*);
+
+		f = 0;
+		bool fileFound = false;
+
+		for (int i = 0; !f && i < numPrefixes; i++)
+		{
+#ifdef _MSC_VER
+			sprintf_s(relativeFileName, maxRelativeFileNameMaxLen, "%s%s", prefix[i], orgFileName);
+#else
+			sprintf(relativeFileName, "%s%s", prefix[i], orgFileName);
+#endif
+			f = fopen(relativeFileName, "rb");
+			if (f)
+			{
+				fileFound = true;
+				break;
+			}
+		}
+		if (f)
+		{
+			fclose(f);
+		}
+
+		return fileFound;
+	}
+	virtual char* readLine(int fileHandle, char* destBuffer, int numBytes)
+	{
+		if (fileHandle>=0 && fileHandle < B3_FILEIO_MAX_FILES)
+		{
+			FILE* f = m_fileHandles[fileHandle];
+			if (f)
+			{
+				return ::fgets(destBuffer, numBytes, m_fileHandles[fileHandle]);
+			}
+		}
+		return 0;
+	}
+	virtual int getFileSize(int fileHandle)
+	{
+		int size = 0;
+		if (fileHandle>=0 && fileHandle < B3_FILEIO_MAX_FILES)
+		{
+			FILE* f = m_fileHandles[fileHandle];
+			if (f)
+			{
+				
+				if (fseek(f, 0, SEEK_END) || (size = ftell(f)) == EOF || fseek(f, 0, SEEK_SET))
+				{
+					printf("Error: Cannot access file to determine size\n");
+				}
+			}
+		}
+		return size;
+	}
+};
+
+#endif //B3_BULLET_DEFAULT_FILE_IO_H