OpenGL SuperBible's example moving very rough

I have compile OpenGL SuperBible 5e’s example of Chapter08\fbo_drawbuffers. The source code is come fomr SVN.

When I move the camera with keyboard, I find that the moving is very rough and I cannot moving the camera with hold 2 key (KEY_UP/KEY_DOWN)+(KEY_LEFT/KEY_RIGHT)

However, I run the original fbo_drawbuffers.exe in which the moving is very smooth.

I also run other chapter’s original exe example. The moving is also very rough.

Anyone know that where is the problem?

Probably the way key presses are handled.
Consider using glutSpecialDownFunc and glutSpecialUpFunc instead of glutSpecialFunc which generate an event for each key repetition done by the OS, this will result in very jerky movement.