paul rosen voicu popescu - pdfs.semanticscholar.org · voicu popescu. 2 class of algorithm •...
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Forward Rasterization
Paul Rosen
Voicu Popescu
2
Class of Algorithm
• Samples are generated by interpolation between the vertices of the primitive.
• Sufficient samples are generated to guarantee that each pixel covered by the primitive receives at least one sample.
• The position on the desired image plane of each sample is recorded with subpixel accuracy using a pair of offsets.
• After all primitives are rasterized and z-buffered, the final image is reconstructed/resampled using the offsets stored with each sample.
3
Frame Buffer Magnification
4
Quadrilateral Rasterization
5
Degenerate Quadrilaterals
6
Triangle Rasterization
• Test interpolation
factors in all 3
sampling directions
• 3rd Edge is a special
case
Interpolation factors for same quadrant edges
Interpolation factors
for edges in different
quadrants
7
Early Discarding
• ED - Discard samples
that land in the same
pixel as the previous
sample
• EDL – Store previous
line of samples
8
Temporal Aliasing
Jittered supersampling Forward Rasterization
9
Temporal Aliasing
10
Depth Buffer Correction
• 2 surfaces close
together
• Move depth sample to
new location
11
Depth Buffer Correction
z = 1m, a = 30o, r = 0.03mm, x16 corr.z = 1m, a = 30o, r = 0.5mm, no corr.
z = 1m, a = 30o, r = 0.125mm, x4 corr.z = 1m, a = 30o, r = 0.125mm, no corr.
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Results – Quad Rasterization
Conventional Rasterization Forward Rasterization
13
Results – Quad Rasterization
1.872.60532.24Median
Overdraw
1.872.60661.72Median
1.902.64651.83Average
2.112.97884.12Max
1.762.44471.35Min
Overdraw
ED
OverdrawInner loop
FWR/CR (%)
Quad
size (pix)
14
Results - Bunny (69Ktris)
Conventional Rasterization Forward Rasterization
15
Results – Dragon (201Ktris)
Conventional Rasterization Forward Rasterization
16
Results – Buddha (292Ktris)
Conventional Rasterization Forward Rasterization
17
Results – Armadillo (346Ktris)
Conventional Rasterization Forward Rasterization
18
Sample Comparison
1.861.2462862.0
2.81.22751121.2Armad.
1.881.3652892.2
2.921.32681191.2Buddha
1.441.3539723.5
2.011.3455902.0Dragon
1.321.2631646.0
1.571.2751753.0Bunny
Overdraw
overall
Overdraw
inside tris.
ED
(%)
Inner loop
FWR/CR (%)
Tri. Size
(pix)
19
Per Pixel Difference
(IFWR – ICR) *127 (ICR - IFWR) *127
Questions?
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