Proposal: Add hextiling nodes

[msuzuki-nvidia]

MaterialX Hextiling Node Proposal

Summary

Hextiling provides tiling a texture image without an obvious repeating pattern. This document proposes two new MaterialX hextiling nodes based on the article "Practical Real-Time Hex-Tiling" (Morten S. et al, 2022) [1].

• <hextiledimage>
• <hextilednormalmap>

The abstract of the article is as follows:

To provide a convenient, easy-to-adopt approach to randomly tiled textures in the context of real-time graphics, we propose an adaptation of the by-example noise algorithm of Heitz and Neyret. The original method preserves contrast using a histogram-preserving method that requires a precomputation step to convert the source texture into a transform and inverse transform texture, which must both be sampled in the shader rather than the original source texture. Thus deep integration into the application is required for this to appear opaque to the author of the shader and material. In our adaptation we omit histogram preservation and replace it with a novel blending method that allows us to sample the original source texture. This omission is particularly sensible for a normal map as it represents the partial derivatives of a height map. In order to diffuse the transition between hex tiles, we introduce a simple metric to adjust the blending weights. For a texture of color, we reduce loss of contrast by applying a contrast function directly to the blending weights. Though our method works for color, we emphasize the use case of normal maps in our work because non-repetitive noise is ideal for mimicking surface detail by perturbing normals.

Unlike standard image tiling, hextiling involves image blending. As described in the abstract above, simple image blending is not suitable for normal maps; therefore, separate nodes for color images and normal maps are necessary.

Parameters

<hextiledimage>

Parameter	Type	Range	Default	Description
file	filename			Image file path
default	color3		(0.0, 0.0, 0.0)	Default color
texcoord	vector2		UV0	Texture coordinate
tiling	vector2		(1.0, 1.0)	Tile repeat
rotation	float	[0, 1]	1.0	Rotation randomness
rotation_range	vector2		(0.0, 360.0)	Range of values used for randomizing rotation
scale	float	[0, 1]	1.0	Scale randomness
scale_range	vector2		(0.5, 2.0)	Range of values used for randomizing scale
offset	float	[0, 1]	1.0	Offset randomness
offset_range	vector2		(0.0, 1.0)	Range of values used for randomizing offset
falloff	float	[0, 1]	0.5	Falloff width for blending tiles
falloff_contrast	float	[0, 1]	0.5	Falloff contrast for blending tiles

<hextilednormalmap>

Parameter	Type	Range	Default	Description
file	filename			Image file path
default	vector3		Nworld	Default normal
texcoord	vector2		UV0	Texture coordinate
tangent	vector3		Tworld	Tangent vector
bitangent	vector3		Bworld	Bitangent vector
tiling	vector2		(1.0, 1.0)	Tile repeat
rotation	float	[0, 1]	1.0	Rotation randomness
rotation_range	vector2		(0.0, 360.0)	Range of values used for randomizing rotation
scale	float	[0, 1]	1.0	Scale randomness
scale_range	vector2		(0.5, 2.0)	Range of values used for randomizing scale
offset	float	[0, 1]	1.0	Offset randomness
offset_range	vector2		(0.0, 1.0)	Range of values used for randomizing offset
falloff	float	[0, 1]	0.5	Falloff width for blending tiles
strength	float	[0, 1]	1.0	Normal map strength

Examples

<hextiledimage>

Rotation (0 - 360)	Scale (0.5 - 2.0)	Offset (0 - 1)
Rotation + Scale + Offset	Tiling (100)

<hextilednormalmap>

Rotation (0 - 360)	Scale (0.5 - 2.0)	Offset (0 - 1)
Rotation + Scale + Offset	Tiling (1 - 100)

References

[1] Morten S. Mikkelsen, Practical Real-Time Hex-Tiling, Journal of Computer Graphics Techniques (JCGT), vol. 11, no. 2, 77-94, 2022, http://jcgt.org/published/0011/03/05/

[msklywenn]

It would be nice to have the stepped offset too:
https://mastodon.gamedev.place/@haukethiessen/110909028684261887