glslViewer keeps the last successfully-compiled shader on screen when a save fails to compile

When glslViewer detects a save, it recompiles the .frag file. If compilation fails, the error with a line number is printed to the terminal but glslViewer does not swap in the broken shader — the previous frame continues rendering on screen. This means a bad save never blanks the window. Recovery is: read the line number in the error message, fix the problem, save again.

Examples

Saving a shader with a missing semicolon prints ERROR: 0:12: ... but the screen keeps showing the last good frame.

Assessment

Explain what happens on screen in glslViewer when you save a shader with a compile error, and state what information the error message gives you.