Displacement mapping
Encyclopedia
Displacement mapping is an alternative computer graphics technique in contrast to bump mapping
, normal mapping
, and parallax mapping
, using a (procedural
-) texture-
or height map
to cause an effect where the actual geometric position of points over the textured surface are displaced, often along the local surface normal
, according to the value the texture function evaluates to at each point on the surface. It gives surfaces a great sense of depth and detail, permitting in particular self-occlusion, self-shadowing
and silhouettes; on the other hand, it is the most costly of this class of techniques owing to the large amount of additional geometry.
For years, displacement mapping was a peculiarity of high-end rendering systems like PhotoRealistic RenderMan
, while realtime APIs
, like OpenGL
and DirectX
, were only starting to use this feature. One of the reasons for this is that the original implementation of displacement mapping required an adaptive tessellation of the surface in order to obtain enough micropolygon
s whose size matched the size of a pixel on the screen.
being used to modulate
the displacement strength. The displacement direction is usually the local surface normal. Today, many renderers allow programmable shading
which can create high quality (multidimensional) procedural texture
s and patterns
at arbitrary high frequencies. The use of the term mapping becomes arguable then, as no texture map is involved anymore. Therefore, the broader term displacement is often used today to refer to a super concept that also includes displacement based on a texture map.
Renderers using the REYES
algorithm
, or similar approaches based on micropolygon
s, have allowed displacement mapping at arbitrary high frequencies since they became available almost 20 years ago.
The first commercially available renderer to implement a micropolygon displacement mapping approach through REYES was Pixar
's PhotoRealistic RenderMan
. Micropolygon renderers commonly tessellate geometry themselves at a granularity suitable for the image being rendered. That is: the modeling application delivers high-level primitives to the renderer. Examples include true NURBS- or subdivision surfaces. The renderer then tessellates this geometry into micropolygons at render time using view-based constraints derived from the image being rendered.
Other renderers that require the modeling application to deliver objects pre-tessellated into arbitrary polygons or even triangles have defined the term displacement mapping as moving the vertices of these polygons. Often the displacement direction is also limited to the surface normal at the vertex. While conceptually similar, those polygons are usually a lot larger than micropolygons. The quality achieved from this approach is thus limited by the geometry's tessellation density a long time before the renderer gets access to it.
This difference between displacement mapping in micropolygon renderers vs. displacement mapping in a non-tessellating (macro)polygon renderers can often lead to confusion in conversations between people whose exposure to each technology or implementation is limited. Even more so, as in recent years, many non-micropolygon renderers have added the ability to do displacement mapping of a quality similar to what a micropolygon renderer is able to deliver, naturally. To distinguish between the crude pre-tessellation-based displacement these renderers did before, the term sub-pixel displacement was introduced to describe this feature.
Sub-pixel displacement commonly refers to finer re-tessellation of geometry that was already tessellated into polygons. This re-tessellation results in micropolygons or often microtriangles. The vertices of these then get moved along their normals to achieve the displacement mapping.
True micropolygon renderers have always been able to do what sub-pixel-displacement achieved only recently, but at a higher quality and in arbitrary displacement directions.
Recent developments seem to indicate that some of the renderers that use sub-pixel displacement move towards supporting higher level geometry too. As the vendors of these renderers are likely to keep using the term sub-pixel displacement, this will probably lead to more obfuscation of what displacement mapping really stands for, in 3D computer graphics
.
In reference to Microsoft's proprietary High Level Shader Language
, displacement mapping can be interpreted as a kind of "vertex-texture mapping" where the values of the texture map do not alter pixel colors (as is much more common), but instead change the position of vertices. Unlike bump, normal and parallax mapping, all of which can be said to "fake" the behavior of displacement mapping, in this way a genuinely rough surface can be produced from a texture. It has to be used in conjunction with adaptive tessellation
techniques (that increases the number of rendered polygons according to current viewing settings) to produce highly detailed meshes.
Bump mapping
Bump mapping is a technique in computer graphics for simulating bumps and wrinkles on the surface of an object. This is achieved by perturbing the surface normals of the object and using the perturbed normal during lighting calculations. The result is an apparently bumpy surface rather than a...
, normal mapping
Normal mapping
In 3D computer graphics, normal mapping, or "Dot3 bump mapping", is a technique used for faking the lighting of bumps and dents. It is used to add details without using more polygons. A common use of this technique is to greatly enhance the appearance and details of a low polygon model by...
, and parallax mapping
Parallax mapping
Parallax mapping is an enhancement of the bump mapping or normal mapping techniques applied to textures in 3D rendering applications such as video games...
, using a (procedural
Procedural texture
A procedural texture is a computer generated image created using an algorithm intended to create a realistic representation of natural elements such as wood, marble, granite, metal, stone, and others....
-) texture-
Texture mapping
Texture mapping is a method for adding detail, surface texture , or color to a computer-generated graphic or 3D model. Its application to 3D graphics was pioneered by Dr Edwin Catmull in his Ph.D. thesis of 1974.-Texture mapping:...
or height map
Heightmap
In computer graphics, a heightmap or heightfield is a raster image used to store values, such as surface elevation data, for display in 3D computer graphics...
to cause an effect where the actual geometric position of points over the textured surface are displaced, often along the local surface normal
Surface normal
A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...
, according to the value the texture function evaluates to at each point on the surface. It gives surfaces a great sense of depth and detail, permitting in particular self-occlusion, self-shadowing
Self-shadowing
Self-Shadowing is a computer graphics lighting effect, used in 3D rendering applications such as computer animation and video games. Self-shadowing allows non-static objects in the environment, such as game characters and interactive objects , to cast shadows on themselves and each other...
and silhouettes; on the other hand, it is the most costly of this class of techniques owing to the large amount of additional geometry.
For years, displacement mapping was a peculiarity of high-end rendering systems like PhotoRealistic RenderMan
PhotoRealistic RenderMan
PhotoRealistic RenderMan, or PRMan for short, is a proprietary photorealistic RenderMan-compliant renderer.It primarily uses the Reyes algorithm but is also fully capable of doing ray tracing and global illumination....
, while realtime APIs
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
, like OpenGL
OpenGL
OpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...
and DirectX
DirectX
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay,...
, were only starting to use this feature. One of the reasons for this is that the original implementation of displacement mapping required an adaptive tessellation of the surface in order to obtain enough micropolygon
Micropolygon
In 3D computer graphics, a micropolygon is a polygon that is very small relative to the image being rendered.Commonly, the size of a micropolygon is close to or even less than the area of a pixel...
s whose size matched the size of a pixel on the screen.
Meaning of the term in different contexts
Displacement mapping includes the term mapping which refers to a texture mapTexture mapping
Texture mapping is a method for adding detail, surface texture , or color to a computer-generated graphic or 3D model. Its application to 3D graphics was pioneered by Dr Edwin Catmull in his Ph.D. thesis of 1974.-Texture mapping:...
being used to modulate
Modulate
Modulate is Bob Mould's fifth solo album, released in 2002. Although a few tracks on his previous release, The Last Dog and Pony Show, had featured tape loops and samples, Mould shocked his fans with such a dramatic embrace of electronica...
the displacement strength. The displacement direction is usually the local surface normal. Today, many renderers allow programmable shading
Shader
In the field of computer graphics, a shader is a computer program that is used primarily to calculate rendering effects on graphics hardware with a high degree of flexibility...
which can create high quality (multidimensional) procedural texture
Procedural texture
A procedural texture is a computer generated image created using an algorithm intended to create a realistic representation of natural elements such as wood, marble, granite, metal, stone, and others....
s and patterns
Texture synthesis
Texture synthesis is the process of algorithmically constructing a large digital image from a small digital sample image by taking advantage of its structural content...
at arbitrary high frequencies. The use of the term mapping becomes arguable then, as no texture map is involved anymore. Therefore, the broader term displacement is often used today to refer to a super concept that also includes displacement based on a texture map.
Renderers using the REYES
Reyes rendering
Reyes rendering is a computer software architecture used in 3D computer graphics to render photo-realistic images. It was developed in the mid-1980s by Loren Carpenter and Robert L. Cook at Lucasfilm's Computer Graphics Research Group, which is now Pixar. It was first used in 1982 to render images...
algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
, or similar approaches based on micropolygon
Micropolygon
In 3D computer graphics, a micropolygon is a polygon that is very small relative to the image being rendered.Commonly, the size of a micropolygon is close to or even less than the area of a pixel...
s, have allowed displacement mapping at arbitrary high frequencies since they became available almost 20 years ago.
The first commercially available renderer to implement a micropolygon displacement mapping approach through REYES was Pixar
Pixar
Pixar Animation Studios, pronounced , is an American computer animation film studio based in Emeryville, California. The studio has earned 26 Academy Awards, seven Golden Globes, and three Grammy Awards, among many other awards and acknowledgments. Its films have made over $6.3 billion worldwide...
's PhotoRealistic RenderMan
PhotoRealistic RenderMan
PhotoRealistic RenderMan, or PRMan for short, is a proprietary photorealistic RenderMan-compliant renderer.It primarily uses the Reyes algorithm but is also fully capable of doing ray tracing and global illumination....
. Micropolygon renderers commonly tessellate geometry themselves at a granularity suitable for the image being rendered. That is: the modeling application delivers high-level primitives to the renderer. Examples include true NURBS- or subdivision surfaces. The renderer then tessellates this geometry into micropolygons at render time using view-based constraints derived from the image being rendered.
Other renderers that require the modeling application to deliver objects pre-tessellated into arbitrary polygons or even triangles have defined the term displacement mapping as moving the vertices of these polygons. Often the displacement direction is also limited to the surface normal at the vertex. While conceptually similar, those polygons are usually a lot larger than micropolygons. The quality achieved from this approach is thus limited by the geometry's tessellation density a long time before the renderer gets access to it.
This difference between displacement mapping in micropolygon renderers vs. displacement mapping in a non-tessellating (macro)polygon renderers can often lead to confusion in conversations between people whose exposure to each technology or implementation is limited. Even more so, as in recent years, many non-micropolygon renderers have added the ability to do displacement mapping of a quality similar to what a micropolygon renderer is able to deliver, naturally. To distinguish between the crude pre-tessellation-based displacement these renderers did before, the term sub-pixel displacement was introduced to describe this feature.
Sub-pixel displacement commonly refers to finer re-tessellation of geometry that was already tessellated into polygons. This re-tessellation results in micropolygons or often microtriangles. The vertices of these then get moved along their normals to achieve the displacement mapping.
True micropolygon renderers have always been able to do what sub-pixel-displacement achieved only recently, but at a higher quality and in arbitrary displacement directions.
Recent developments seem to indicate that some of the renderers that use sub-pixel displacement move towards supporting higher level geometry too. As the vendors of these renderers are likely to keep using the term sub-pixel displacement, this will probably lead to more obfuscation of what displacement mapping really stands for, in 3D computer graphics
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
.
In reference to Microsoft's proprietary High Level Shader Language
High Level Shader Language
The High Level Shader Language or High Level Shading Language is a proprietary shading language developed by Microsoft for use with the Microsoft Direct3D API. It is analogous to the GLSL shading language used with the OpenGL standard...
, displacement mapping can be interpreted as a kind of "vertex-texture mapping" where the values of the texture map do not alter pixel colors (as is much more common), but instead change the position of vertices. Unlike bump, normal and parallax mapping, all of which can be said to "fake" the behavior of displacement mapping, in this way a genuinely rough surface can be produced from a texture. It has to be used in conjunction with adaptive tessellation
Tessellation
A tessellation or tiling of the plane is a pattern of plane figures that fills the plane with no overlaps and no gaps. One may also speak of tessellations of parts of the plane or of other surfaces. Generalizations to higher dimensions are also possible. Tessellations frequently appeared in the art...
techniques (that increases the number of rendered polygons according to current viewing settings) to produce highly detailed meshes.
Further reading
- Blender Displacement Mapping
- Relief Texture Mapping website
- Real-Time Relief Mapping on Arbitrary Polygonal Surfaces paper
- Relief Mapping of Non-Height-Field Surface Details paper
- Steep Parallax Mapping website
- State of the art of displacement mapping on the gpu paper
See also
- Texture mappingTexture mappingTexture mapping is a method for adding detail, surface texture , or color to a computer-generated graphic or 3D model. Its application to 3D graphics was pioneered by Dr Edwin Catmull in his Ph.D. thesis of 1974.-Texture mapping:...
- Bump mappingBump mappingBump mapping is a technique in computer graphics for simulating bumps and wrinkles on the surface of an object. This is achieved by perturbing the surface normals of the object and using the perturbed normal during lighting calculations. The result is an apparently bumpy surface rather than a...
- Normal mappingNormal mappingIn 3D computer graphics, normal mapping, or "Dot3 bump mapping", is a technique used for faking the lighting of bumps and dents. It is used to add details without using more polygons. A common use of this technique is to greatly enhance the appearance and details of a low polygon model by...
- Parallax mappingParallax mappingParallax mapping is an enhancement of the bump mapping or normal mapping techniques applied to textures in 3D rendering applications such as video games...
- Relief mapping (computer graphics)
- HeightmapHeightmapIn computer graphics, a heightmap or heightfield is a raster image used to store values, such as surface elevation data, for display in 3D computer graphics...
- Sculpted primSculpted primA sculpted prim is a Second Life 3D parametric object whose 3D shape is determined by a texture. These textures are UV maps that form the rendered 3D sculpted prim...