Displacement Mapping

```4.10. DISPLACEMENT MAPPING
Exploration of bump, parallax, relief and displacement mapping
Overview of Tangent Space
Tangent Space
In order to understand bump mapping it is
firstly necessary to understand tangent space.
Common coordinate spaces (and transforms)
are as shown opposite.
The view matrix converts from world space to
view space, with the projection matrix
converting view eye space into clip space.
After clip space, coordinates undergo
perspective divide and a viewport
transformation, ultimately resulting in
“window coordinates”.
TBN Matrix
Model Matrix
View Matrix
Projection Matrix
Tangent Space
Tangent space is
the coordinate
space local to the
surface of the
model.
For a single quad,
tangent space is
the coordinate
space formed by
the two tangent
vectors along the
S and T axis, and
the surface
normal.
Tangent Space
A TBN matrix converts from object space
to tangent space. It is build as:
(where S and T are the tangents and N the
normal).
Different forms of
Displacement Mapping
Video not available in on-line slides
Introduction to Bump Mapping
Bump mapping is a technique which adds surface ‘roughness’, improving
the visual fidelity of minute surface detail which would otherwise require a
large number of polygons to model.
A bump map is a form of texture that
holds bump information. Commonly ,
a bump map stores a height field (e.g.
A greyscale image where the
brightness of each pixel holds the
intended surface height)
Bump mapping techniques operate
by changing how a particular pixel is
lit or textured based on the view
angle and the stored height
information.
Introduction to Bump Mapping
Within standard rendering,
the object’s geometric
surface normal is calculated
for each pixel to be rendered.
This normal controls how
light interacts with the object
(e.g. within Phong shading).
A bump map can be used to
calculate the surface normal
of the height map, modifying
the calculated normal and
effecting how the pixel is lit.
The height map may also be
used to control which part of
a diffuse texture is used to
texture the pixel.
Introduction to Bump Mapping
A range of different types of bump mapping algorithm exist.
•
Normal mapping offers the most simple form of bump mapping
technique.
•
Parallax mapping offers a slightly more complex approach.
•
Relief mapping (or parallax occlusion mapping) is a more complex form
of parallax mapping using simple ray tracing.
•
Displacement mapping is a more true form of bump mapping that
modifies the position of vertices.
Simple forms of bump mapping only perturb
the surface normals. The more complex forms
of bump mapping provide bumpy silhouettes
Normal Mapping
A normal map holds (in the
RGB channels) the X, Y and Z
coordinate tangent space
normals.
The normal map is used to
provide a more accurate perpixel normal when
calculating the intensity of
the light on that surface.
This provides the illusion of
considerably more fine
surface detail.
Parallax Mapping
Parallax mapping (also called offset mapping) extends basic normal
mapping and provides more apparent depth. There are several different
types of parallax mapping, including:
•
•
•
•
•
•
Offset and Offset with Limiting
Iterative parallax
Parallax occlusion
Relief
Cone step
Steep parallax
Basic parallax mapping (offset and iterative) is a single step process which
does not take into account occlusion. Later extensions incorporate iterative
approaches which permit occlusion and accurate silhouette rendering.
However, it is only now that such approaches are becoming feasible on
current hardware.
Parallax Mapping
Parallax mapping changes the texture lookup coordinates by introducing a
displacement based on the tangent space viewing angle and the height
space value.
At steeper view-angles, the texture coordinates are displaced more, giving
the illusion of depth due to parallax effects as the view changes.
Basic parallax mapping looks
good on any relatively large
surface viewed from nonoblique angles (e.g. walls
and floors). It's not good for
steep edges, because of the
distortion
Relief Mapping / Parallax Occlusion Mapping
Relief mapping is one name (also
including steep parallax mapping
and parallax occlusion mapping) for a
class of algorithms that trace rays
against a height field.
The basic approach is to walk along a
ray which has entered the height
field's volume and find the first point
of intersection with the height field.
Relief Mapping / Parallax Occlusion Mapping
Various techniques have
been proposed to speed up
the ray trace by taking
variable step sizes.
Relief mapping is capable
of providing surface selfocclusion, self-shadowing,
view-motion parallax and
silhouettes.
Video not available in on-line slides
Video not available in on-line slides
Parallax Occlusion Mapping
Explore the DirectX SDK Parallax Occlusion Mapping sample
Displacement Mapping
Displacement mapping modifies the actual geometric position of points over
a textured surface (typically along the surface normal).
It provides self-occlusion, selfshadowing and silhouettes.
However, it is also a costly mapping
process as additional geometry must
be introduced as part of an adaptive
tessellation (increasing the number
of rendered polygons) to produce a
more highly detailed mesh.
Directed reading regarding bump mapping
Directed reading: Bump Mapping
• Read Displacement Mapping on the GPU —
State of the Art – for an excellent overview of
different displacement mapping techniques
(bump, parallax, displacement, etc.).
• Read Detailed Shape Representation with
Parallax Mapping – for the initial formulation of
parallax mapping
• Read ShaderX3 - Parallax Occlusion Mapping –
for the initial formulation of parallax occlusion
mapping
• Read Displacement Mapping – for coverage of
true displacement mapping
Directed reading: Bump Mapping
For a selection of interesting papers on advanced
approaches for parallax mapping read:
• Prism Parallax Occlusion Mapping with Accurate
Silhouette Generation
• Real-Time Relief Mapping on Arbitrary Polygonal
Surfaces
• Relief Mapping of Non-Height-Field Surface Details
• Dynamic Parallax Occlusion Mapping with Approximate
• GPU Gems 2 - Per-Pixel Displacement Mapping with
Distance Functions
• GPU Gems 3 - Relaxed Cone Stepping for Relief
Mapping
Summary
Today we
explored:
 Different
types of
bump/
displacement
mapping.
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