OpenGl

occlusion

depth-buffering (glEnable(GL_DEPTH_TEST))

linear perspective

relative size

relative height

perspective projection (gluPerspective)

texture gradient

perspective, texture mapping (glTexImage2D, etc)

shading, shadows

lighting (glLight, glMaterial, glNormal)

aerial perspective

fog (glFog)

accomodation

accumulation buffer

stereo parallax

quad-buffering, color-masking

motion parallax

transformations