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Rasterization Parameter
Interpolation

Overview

Screen-space
interpolation

Screen-space
interpolation

Screen-space
interpolation

Persp. corr.
interpolation

Perspectively correct
interpolation of parameter “r”

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Rasterization Parameter
Interpolation

Overview

screen-space interpolation

perspectively-correct
interpolation

Screen-space
interpolation

Given

image plane coordinates of 3
vertices

(u0, v0),
(u1, v1), (u2, v2)

rasterization parameter value
at the 3 vertices

(r0, r1,
r2)

Find

coefficients of linear
expression

au + bv +c = r

Screen-space
interpolation

Screen-space
interpolation

using barycentric interpolation

r is any rasterization
parameter (red, green, blue, 1/z, z, s, t, nx, ny, nz)

1/z is the only parameter
linear in screen space, for others it is an approximation

Persp. corr.
interpolation

Linear interpolation in
triangle plane rather than in image plane

pick convenient 2D coordinate
system

choose axes V2V1
and V3V1

P has coordinates (k, l)

P=V1+(V2-V1)k+(V3-V1)l

r = r1+(r2-r1)k+(r3-r1)l

Perspectively correct
interpolation of parameter “r”

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Second level

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Overview

•

screen-space interpolation

•

perspectively-correct interpolation

Screen-space interpolation

•

Given

–

image plane coordinates of 3 vertices

(u0, v0), (u1, v1),
(u2, v2)

–

rasterization parameter value at the 3 vertices

(r0, r1, r2)

•

Find

–

coefficients of linear expression

au + bv +c = r