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\subsection{Basis textures} |
\subsection{Basis textures} |
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We call the textures assigned to each OpenGL texture unit {\em basis textures}. |
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In order to avoid shapes or features from the basis textures becoming |
In order to avoid shapes or features from the basis textures becoming |
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identifiable, the basis textures should be relatively uniform. |
identifiable, the basis textures should be relatively uniform. |
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We have obtained good results with a mix of |
We have obtained good results with a mix of |
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small textures with uniformly random texels, |
small textures with uniformly random texels, |
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larger textures with noise or turbulence\cite{perlin-noise-intro}, |
larger textures with noise or turbulence\cite{perlin-noise-intro}, |
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and simple geometric images (checkerboard, cone). |
and simple geometric images (e.g. checkerboard). |
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As for selection of basis textures for each paper, the principle of ``saving bits'' applies: |
As for selection of basis textures for each paper, the principle of ``saving bits'' applies: |
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using hyperparameters for each paper to control the probabilities of |
using hyperparameters for each paper to control the probabilities of |
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\subsection{Texture coordinates} |
\subsection{Texture coordinates} |
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Basic choice: finite repeating unit or not? |
Texture coordinates define the mapping of the basis textures to the paper. |
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Each basis texture is repeating, but by choosing the texture coordinates |
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Absolute scale --- sharp/blur |
appropriately we can make the final paper repeating or not. |
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If the paper will be used only at relatively few magnifications, it is |
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Repeating unit |
useful to use a repeating paper because of saving bits. |
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On the other hand, for user interfaces where zooming at widely different |
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{\bf tjl} |
scales is desirable, a non-repeating paper can be better. |
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In order to create more interesting textures, it can also be useful |
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to use repeating units for non-repeating papers --- but use more than one, |
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which are not rationally related. |
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The choice of the repeating unit fixes an absolute scale to the paper. |
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The repeating unit should be relatively isotropic to avoid |
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the degeneration of textures to diagonal lines. |
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After a repeating unit is fixed, there is still |
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freedom in choosing |
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textures coordinates for each texture |
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unit: any mapping of the texture is fine, as long as it repeats |
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with the selected repeating unit. |
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\subsection{Register combiners} |
\subsection{Register combiners} |
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