Texture Mapping Intermediate

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Texture Mapping (Intermediate)

• Jyun-Ming Chen

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Texture Suite
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Texture Suite
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Outline

• Dynamic sub texture image
• 1D and 3D textures
• Render to texture

• Environment mapping
• Cubemap
• Spheremap
• Bump map
• Light map
• Projective texture
• Q coord

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Dynamic Texture
A better way of doing it Render-to-texture (RTT)
with framebuffer object (FBO)

• CopyTexSubImage2D
• Replace a rectangular portion of 2D texture with
  pixels from the current READ_BUFFER
• This involves a read-back from GPU to CPU.

Can you think of a way to move the dynamic
texture around?!
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glTexSubImage2D

• Replace part of the original image as new
  subimage
• Width and size of image need not be 2n
• E.g., dynamic texture

glTexSubImage2D (target, level, xoffset,
yoffset, width, height, format, type, pixels)
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Other Related Functions
Similar to glCopyPixels

• void glCopyTexImage2D(target, level,
  internalformat, x, y, width, height, border)
• defines a two-dimensional texture image with
  pixels from the current GL_READ_BUFFER.
• void glCopyTexSubImage2D(target, level, xoffset,
  yoffset, x, y, width, height) doc
• replaces a rectangular portion of a
  two-dimensional texture image with pixels from
  the current GL_READ_BUFFER (rather than from main
  memory, as is the case for glTexSubImage2D).

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3D Textures
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Render-to-Texture (RTT)

• Generate a snapshot every q degrees
• Total 360/q shots
• The shots are stored as a single texture
• Width and height must be 2n
• E.g., 128x128x8, q45

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RTT Implementation

• First determine a viewing range such that all
  views are rendered well.
• The snapshots are taken from slightly elevated
  positions.
• At each position, pre-render to some 2n
  resolution, copy the image to buffer
• When the panorama is done, set all pixels with
  background color to zero alpha values. Bind it to
  a texture object.

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RTT

• The image version of the model will be set on a
  (cylindrical) billboard
• The texture can be chosen as follows

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If you tank is symmetric, you can use even fewer
images
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RTT (symmetric tank)
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0

• 180?8 images (180/7?26) apart
• port side
• starboard side
• Reverse the port-side image

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f
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f
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Perlin Noise
3D Texture Noise as texture
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Light Map

• By Michael Gold (ref)
• NVIDIA

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Light Maps
Quake (????, id software) was the first computer
game to use light map
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(No Transcript)
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Lightmaps

• Cached Lighting Results
• Reuse lighting calculations
• Multiple local lights (same type)
• Static portion of scenes light field
• Sample region with texture instead of tessellating

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Lightmaps

• Getting the most from the Lightmap
• Maximize lightmap re-use, minimize lightmap size
• Texture size versus sampling level
• Full surface texture with built-in lighting
• Small surface texture, small low-resolution
  lightmap
• Adjust texture matrix to re-use lightmap
• Dynamic lighting track moving lights

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Lightmaps

• Segmenting Scene Lighting
• Static vs. dynamic light fields
• Global vs. local lighting
• Similar light shape

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Lightmaps

• Segmenting the lightfields

Dominant Lighting
Local lighting
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Lightmaps

• Moving Local Lights
• Recreate the texture simple but slow
• Manipulate the lightmap
• Translate to move relative to the surface
• Scale to change spot size
• Change base polygon color to adjust intensity
• Projective textures ideal for spotlights

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Lightmaps

• Moving Local Lights

Translate Texture
Scale Texture
Change Base Polygon Intensity
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Lightmaps

• Creating a lightmap
• Light white, tesselated surface with local light
• Render, capture image as texture
• Texture contains ambient and diffuse lighting
• Texture can also be computed analytically

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Lightmaps

• Creating a lightmap

Render surface lit by local light
Create a Texture Map from Image
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Lightmaps

• Lightmap building tips
• Minimize texture resolution to match required
  sampling
• Edges of texture should have uniform intensity
• Light intensity change should be negligible at
  edges
• Dont forget borders if you clamp the lightmap
• Fill in border to match edge and corner
• Or use border color

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Lightmaps

• Lightmap building tips

Boundary should have constant value
Intensity changes from light should be
minimal near edge of lightmap
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Lightmaps

• Lighting with a Lightmap
• Local light is affected by surface color and
  texture
• Two step process adds local light contribution
• Modulate textured, unlit surfaces with lightmap
• Add locally lit image to scene
• Can mix OpenGL, lightmap lighting in same scene

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Lightmaps
Lightmap

• Creating local contribution

Unlit Scene
Local Light Contribution
Lightmap Intensity
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Lightmaps

• Using Lightmaps
• Move lightmaps using texture matrix
• Distance from surface simulated by scaling
  texture and changing intensity
• Texgen maps lightmap to surfaces, overrides local
  texture coordinates
• Can avoid changing models texture coordinates

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Projective Texture Mapping
Also generate shadows
Light source as slide projector
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Projective Texture Mapping
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Implementation Tricks

• The projected texture need to be padded with
  black boundary pixels so that the clamped texture
  appears Ok
• Some natural faults (more than one layer of
  surface got textured) no way to resolve this!?

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Q coord

• See Sampcode/qcoord

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Sphere Map
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Sphere Map (cont)
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Generating Sphere Map (ref)
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Adding Silhouettes with Sphere Map
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Reflection Mapping (wikipedia)

• the most common ones are the Standard Environment
  Mapping in which a single texture contains the
  image of the surrounding as reflected on a mirror
  ball, or the Cubic Environment Mapping in which
  the envirornment is unfolded onto the six faces
  of a cube and stored therefore as six square
  textures.
• A typical drawback of this technique is the
  absence of self reflections you cannot see any
  part of the reflected object inside the
  reflection itself.

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Spheremap

• involves the use of a textured sphere infinitely
  far away from the object that reflects it. By
  creating a spherical texture using a fisheye lens
  or via prerendering or with a light probe, this
  texture is mapped to a hollow sphere, and the
  texel colors are determined by calculating the
  light vectors from the points on the object to
  the texels in the environment map. This technique
  may produce results which are superficially
  similar to those produced by raytracing, but
  incurs less of a performance hit because all of
  the colors of the points to be referenced are
  known beforehand, so all it has to do is to
  calculate the angles of incidence and reflection.
• There are a few glaring limitations to spherical
  mapping. For one thing, due to the nature of the
  texture used for the map, there is an abrupt
  point of singularity on the backside of objects
  using spherical mapping. Cube mapping (see below)
  was developed to address this issue. Since cube
  maps (if made and filtered correctly) have no
  visible seams, they are an obvious successor to
  the archaic sphere maps, and nowadays spherical
  environment maps are almost nonexistent in
  certain contemporary graphical applications, such
  as video game graphics.

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Cube Mapping

• Cube mapped reflection is a technique that uses
  cube mapping to make objects look like they
  reflect the environment around them. Generally,
  this is done with the same skybox that is used in
  outdoor renderings. Though this is not a true
  reflection since objects around the reflective
  one will not be seen in the reflection, the
  desired effect is usually achieved.
• Cube mapped reflection is done by determining the
  vector that the object is being viewed at. This
  camera ray is reflected about the surface normal
  of where the camera vector intersects the object.
  This results in the reflected ray which is then
  passed to the cube map to get the texel which the
  camera then sees as if it is on the surface of
  the object. This creates the effect that the
  object is reflective.

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Dynamic Cube Map
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Reference

• here

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Code Samples
lightmap

• Cutout texture
• Render-to-texture (RTT)
• Whirlpool

billboarding
cubemap