Sentence Structure

The following is a part of a paragraph from the novel "Night and Day" by Woolf. I cannot figure out the role of "what".

"Sudden stabs of unmitigated truth assailed him now and then, for he was not inclined by nature to take a rosy view of his conduct, but what with the beat of his foot upon the pavement and the glimpse of half-drawn curtains offered him of kitchens, dining-rooms and drawing-rooms, illustrating with mute power different scenes from different lives, his own experience lost its sharpness."

I'd greatly appreciate if you could mark the different fragments of the piece.

Are "what" and "glimpse" the subjects of the verb "illustrate"?

Thanks in advance
Nikoo