Analysis of the principle of creating the shadow of the box

Make the shadow of this box, the light from the left 45 degrees angle incidence:

Using the previous projective theorem to determine the angle and position of the projection with the auxiliary line:

The completion of the location of the determination, in fact, I now want to determine the relationship between the light distribution of an object, usually directly with the help of 3D software, in the 3D software ...

L1,L2 two lines from point A, one parallel to the light source and one to normal:

Continue to make diagram guides:

Continue to connect the points, to get the green three points in the figure, in contrast to the above effect chart, these three points are above the box on both sides of the cast:

Continue to make DC projections on planes and boxes, at which point two blue dots are obtained:

Connect the green and blue dots, and get the projection of the face acdb:

Create a selection and fill it, a surface projection is done, the other side of the principle is the same, may be 3D of people is superfluous, but still hope ...