@Lance:
I don't quite follow what you're saying, could you provide a paint over?
Sarkut wrote:This latest image is a great improvement over the first.
It is interesting to see the lower right vanishing point being used to define
the internal structure of the sunbeam, as it relates to architecture of the room.
I believe that the outer boundaries of the beam should be determined
by the single vanishing point (the sun) as limited by the window opening.
(The green lines.)
The red lines here show how the light isn't conforming to that idea.
http://img230.imageshack.us/img230/7/hjgfjjffjjff.png
Ah, I also initially reached this conclusion. It's wrong, but not in a way that is immediately obvious. I found there were two issues with this way of drawing the sunbeam, and finding a solution that resolved them both kept me up quite late.
1) Consider what would happen to your green edges if the window was say, shaped like a triangle? The way you have the edges set up, the shape of the sunbeam would not change.
2) Perhaps more importantly, the edge of the sunbeam on the floor is shown by the red lines here:
But, how do you know that the edge should not really be the blue line? Or the green line?
The issue is resolved when you consider what is really happening:
The individual rays are going past the points on the top edge of the window (The blue dots) and hitting (And stopping at!) the orange dots. It should be obvious that the orange dots trace a line, and it is the vanishing point of that line that we want to find.
The line traced by the orange dots lies both on the plane of the wall, and the plane traced by the red dotted lines. We want to find the vanishing point of the line which is the intersection of these planes. The green line is the set of all vanishing points which lie on the plane of the wall. It is parallel to vertical edges of the wall and goes through the primary vanishing point. The red line is parallel to the line traced by the blue points, in this case the horizontal edge of the window, and it passes through the vanishing point of the sun's rays. The vanishing point for the line of orange dots will be the only vanishing point found on both planes: the point where the green and yellow lines intersect!
From here, consult my previous post as to how I drew the sunbeams.
On last thing, what if the window were some odd shape? You would set up the vanishing points like this (you have a few more now you notice, and they are all used to determine the edges on the various planes of the walls):
I leave it as an exercise to the reader to figure out how to use those three additional vanishing points.
Ben_R_R
