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Class7

# Class7 - Class 7 Screen-Space Interpolation with...

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Class 7. Screen-Space Interpolation with Perspective Correction Ulrich Neumann CS580 (Computer Graphics Rendering)

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Problem Can we interpolate image space parameters over triangles in screen space? NO : accurate surface parameter interpolation has to take perspective into account. Line on screen in perspective shrinks most of the range into the last few pixels.
Checkerboard Example Checkerboard defined as integer grid red over odd/odd (o, o) and even/even (e, e) intervals black over odd/even intervals (e, o), (o, e) Image midpoint is not actual midpoint of checkerboard Straight line along diagonal stays straight under perspective Linear Interpolation Perspective Interpolation Mid-image checkerboard interpolation point is not mid-object Correct mid-checkerboard interpolation to mid-object 0,0 2,2 2,0 0,2 0,1 2,1 1,0 1,2

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Parameter Interpolation Similarly, linear interpolation of affine (image space) parameters like Z give wrong result Interpolation of perspective Z is correct (all HW so far) we can recover image space result if we Xform perspective Z back to image (affine) space after interpolation Effect is modest for scene like teapot where Z range is small, or with narrow FOV Roads to horizon, grazing angles on slightly curved surface like a car hood, and wide FOV cameras produce a more dramatic impact Need correct interpolation of u,v texture coords in HW5 Z=1 Z = 11 Z = 21 a b c Z= -d Z= 0
Color and Normal interpolation

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Class7 - Class 7 Screen-Space Interpolation with...

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