output file does not properly detect file extension

[milesmj]

I just got this to compile on my apple M1 (arm) laptop, but I had to fix this bug first. I was compressing with bc7 to a ktx or dds texture, and it would always end up stored as uncompressed. I dug into the source and found a bug when detecting if the destination file is compressed or not:

cmp_fileio.cpp

std::string CMP_GetJustFileExt(const std::string& sourceFile)
{
    std::string fileExt = "";

#if defined _CMP_CPP17_ || defined _CMP_CPP14_
    sfs::path fp(sourceFile);
    fileExt = fp.extension().string();
#else
    // Alternate Code
    fileExt = sourceFile.substr(sourceFile.find_last_of('.') + 1); // ***** ERROR HERE ***** should not add one. period should be included in result
#endif

    return fileExt;
}

The return from this function expects the '.' to be included, but the alternate code here will strip the '.'. You can see where this function expects the '.' here:

textureio.cpp

bool IsDestinationUnCompressed(const char* fname)
{
    bool        isuncompressed = true;
    std::string file_extension = CMP_GetJustFileExt(fname);

    // tolower
    for (char& c : file_extension)
        c = tolower(c);

    if (file_extension.compare(".dds") == 0)
    {
        isuncompressed = false;
    }
    else if (file_extension.compare(".astc") == 0)
    {
        isuncompressed = false;
    }
<more code>
}

[denislevesqueAMD]

@milesmj Good catch!

That function is used in a few places in less than ideal ways. I think the best solution would be to replace all uses of that function with CMP_GetFileExtension since it allows for more customization of the result, would reduce a lot duplicated code (like always converting the result of CMP_GetJustFileExt to upper or lower case), and fix the bug.