Lesson 13
Parallax Occlusion Mapping
PV227 – GPU Rendering
Jiˇrí Chmelík, Jan ˇCejka
Fakulta informatiky Masarykovy univerzity
12. 12. 2016
PV227 – GPU Rendering (FI MUNI) Lesson 13 – POM 12. 12. 2016 1 / 15
Parallax Occlusion Mapping
Nothing Normal mapping Parallax Occlusion
Mapping
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Basic principle
Basic principle
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Parallax direction
We work in the tangent space (ts) (on the surface of the object)
parallax dir (ts) = ray dir.xy (ts)
PV227 – GPU Rendering (FI MUNI) Lesson 13 – POM 12. 12. 2016 4 / 15
Maximal parallax
ray (ts)
depth scale
=
ray dir (ts)
−ray dir.z (ts)
ray (ws)
depth scale
=
ray dir (ws)
−ray dir.z (ts)
parallax (ts) = ray.xy (ts)
PV227 – GPU Rendering (FI MUNI) Lesson 13 – POM 12. 12. 2016 5 / 15
Texture space
Our space with texture coordinates is a little different from the
tangent space
Directions of tangents and bitangents are the same as directions
of s and t coordinates
The sizes are different
parallax (texs) = ts_to_texs · parallax (ts)
PV227 – GPU Rendering (FI MUNI) Lesson 13 – POM 12. 12. 2016 6 / 15
Sampling
Sample the height texture to find the first intersectoion
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Algorithm
for sample i do
percentage ← i/#samples
sample_tex_coord ← tex_coord0 + parallax_texs · percentage
tex_depth ← one_minus_sample(height_tex, sample_tex_coord)
ray_depth ← percentage
if ray_depth > tex_depth then
break
end
end
Use last percentage to compute the final texture coordinate and
position.
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Task: Implement POM
Task 1: Implement this algorithm
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Task: Improve POM
Task 2: Compute the intersection more precisely
Result: Better result with less samples
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Interaction with other objects
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Task: Improve interaction with other objects
Task 3: Adjust fragment’s depth
Transform offseted position into clip space (transform in with view
and projection matrices)
Transform it into normalized device coordinates (divide it with its w)
Transform it from [−1, 1] to [0, 1]
Store its z into gl_FragDepth
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Task: Improve interaction with other objects
Without depth adjustment With depth adjustment
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Task: Self-shadowing
Task 4: Implement self-shadowing
Cast another ray from the offseted position to the light
Check whether there is an obstacle in the height map
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Task: Self-shadowing
Without self-shadows With self-shadows
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