View source for GPU/Procedural Texture Generation

[[Category:GPU]]
The 3DS GPU supports procedural generation of texture data using [[GPU/Internal_Registers#GPUREG_TEXUNIT3_PROCTEX0|texture unit 3]]. Little is known about this feature, albeit a few public hints have been dropped. The contents of this page are solely based on reports on a [http://www.4gamer.net/games/017/G001762/20120822007/ presentation] given by DMP.

The related GPU registers can be found starting [[GPU/Internal_Registers#GPUREG_TEXUNIT3_PROCTEX0|here]].

== Overview ==
Procedural texture generation has four stages:
* Noise Module (outputs u&prime;,v&prime;)
* Repeat Module (outputs u&prime;&prime;,v&prime;&prime;)
* Base Shape (also notated as G(u&prime;&prime;,v&prime;&prime;), output g)
* F(g) and Lookup Table

== Noise Module ==
This stage applies noise on the input coordinates. Little is known about this other than that there are three noise parameters:
* Amplitude
* Frequency
* Phase

These parameters are configured starting [[GPU/Internal_Registers#GPUREG_TEXUNIT3_PROCTEX1|here]].

== Repeat Module ==
This stage performs basic texture coordinate wrapping on the noised coordinates. It supports symmetric and mirrored wrapping. They don't seem to be configurable beyond that.

== Base Shape ==

The U&rsquo;&rsquo; and V&rsquo;&rsquo; coordinates are used to generate a scalar value in the range [0;1] from the wrapped coordinates using one of six functions documented [[GPU/Internal_Registers#GPUREG_TEXUNIT3_PROCTEX0|here]].

The output of this function is named "g".

== F(g) and Lookup Table ==

F is a selectable function which transforms g to another scalar value. There are two known options for F:
* the identity function
* a triangle function

The final texel color is determined by using the value of F(g) as an index into a configurable [[GPU/Internal_Registers#GPUREG_PROCTEX_LUT|lookup table]].