[Vocabulary] drifted up/rectangle of light

[sherishine]

The rectangle of light that had drifted up Caravaggio’s chair was framing his chest and head so that to the English patient the face seemed a portrait. In muted light his hair appeared dark, but now the wild hair lit up, bright, the bags under his eyes washed out in the pink late daylight.

He had turned the chair around so he could lean forward on its back, facing Almasy. Words did not emerge easily from Caravaggio. He would rub his jaw, his face creasing up, the eyes closed, to think in darkness, and only then would he blurt out something, tearing himself away from his own thoughts. It was this darkness that showed in him as he sat in the rhomboid frame of light, hunched over a chair beside Almasy’s bed. One of the two older men in this story.
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The above is from the English Patient.

:?:
I just can't see the clear picture of it. What does the"drifted up" mean? Does that"rectangle of light "actually means "rectangle of shadow"?

 

[Tdol]

No, I don't think so; it means the light, coming through a door or something to give it the shape, moved up and changed the way the person looked.

 

[BobK]

:up: It didn't just drift aimlessly and randomly. It moved because the source moved - maybe the sun was going down. Caravaggio's face, previously in shadow, came to be bathed in light, as if it were a portrait (with the edge of the rectangle being, in effect, a picture-frame).

b

 

[sherishine]

Many thanks for your explaination, now I can understand it ;-)