Writing pen, drawing 3d with 2-color pen is like a 3d screen that projects 2 red and blue and we wear a color filter with 1 color to produce a 3d image.
Writing pen, drawing 3d with 2-color pen is like a 3d screen that projects 2 red and blue and we wear a color filter with 1 color to produce a 3d image. move the two nibs far apart and close together, so to create the difference between the two colors being close together or apart.because if the object is close, the deviation of the two eyes is more or less. pair of 2 rays intersect.the object near the 2 cut close rays should create a lot of deviation, so we fake the deviation to see near and far, then wear a color filter to see the 3d image like a 3d screen