Perspective Views

Learn about perspective views.

one point view

image plane is parallel to one face

two point view

image plane is parallel to one axis, usually y

three point view

most general case

what shape is the view volume

frustum

in what 3 cases will primitives need to be clipped?

outside field of view, too close to camera, too far from camera

role of N matrix from NSH

performs perspective normalisation. for parallel projections, set to identity matrix

role of S matrix from NSH

performs scaling to normalised device coords. if normalised, set to identity matrix

role of H matrix from NSH

transforms the frustum to a symmetric form (shears). if projection is not oblique, set to identity matrix

which primitives are rendered and which are culled?

those facing the camera are rendered, those facing the other way are culled

z buffer

selectively renders based on partial information

why is the z buffer the only suitable approach for modern pipelined hardware?

vertices arrive in random order so we need to sort them at the end of the process

depth buffer (in z buffer algorithm)

records the distance from the closest fragment to the projection plane

z buffer algorithm step 1 (before updating colour buffer)

check depth of current fragment

z buffer algorithm step 2 (before updating colour buffer)

compare to recorded closest depth

z buffer algorithm step 3 (before updating colour buffer)

if larger, discard the colour. if smaller, update the colour and depth

how is a shadow like a projection?

a 3d object casts polygonal shadows, where the polygon is a projection of the 3d object onto a flat surface