Hedgehog Engine - Textures

Hedgehog Engine 1 games limit themselves to a few texture types (with exceptions), which can make configuring materials difficult, as many shaders use certain types differently than what their name suggests.

Here is a list of all texture types and how they are most commonly used:

Type	Primarily used with	Occasionally used with
diffuse	Diffuse	Emission
opacity	Opacity	Diffuse
reflection	Environment Map	/
specular	Specular	Diffuse, Gloss
gloss	Gloss	Diffuse, Specular
normal	Normal map	/
displacement	General use texture type	Falloff, Emission

File formats and encodings

Textures are always stored in DDS files, of which the vast majority use some form of block-compression encoding. Only a handful are not compressed.

Since HE1 is programmed with Direct3D 9, the number of available block compression encodings is limited to BC1, BC2 and BC3.

More info on DDS block compression can be found here.

Note

The Direct3D 11 mod for Sonic Generations (PC) by Skyth makes the game run on Direct3D 11, which can read newer DDS encodings like BC4, BC5, BC6, BC7 and more.

Kinds of textures

The majority of textures used by materials are one of the following kind of textures.

Diffuse

Texture overview
File Suffix	_dif
Composition	RGBA
Recommended encoding	BC1_UNORM when opaque, BC3_UNORM when transparent

chr_sonic_body01_dif_HD.dds from Sonic Generations

Diffuse textures are color-transparency textures that are sampled directly for the base color of a material.

Opacity

Texture overview
File Suffix	_alp, _a, often none at all
Composition	Grayscale
Recommended encoding	BC1_UNORM

csc_etc_ty1_wind01_alp.dds from Sonic Generations

Opacity textures determine the transparency of a material.

Usually transparency is relayed to Diffuse textures, and actual opacity textures are only used when special alpha compositing happens.

Falloff

Texture overview
File Suffix	_fal
Composition	Color
Recommended encoding	BC1_UNORM

chr_sonic_body01_fal_HD.dds from Sonic Generations

A camera rotating around Suzanne with a raw falloff factor. The diffuse texture is black, and the falloff texture is white

Falloff textures change the color of the diffuse texture based on the viewing angle: The greater the angle between the camera and the surface of the model, the greater the influence.

Depending on the shader, the falloff color either gets mixed with the diffuse color or added to it.

Additionally, shaders with falloff colors or textures basically always come with a parameter that controls how the falloff factor gets calculated.

Environment map

Texture overview
File Suffix	_ref, _env, _cube
Composition	RGBA
Recommended encoding	BC1_UNORM when opaque, BC3_UNORM when transparent

Environment textures are used to project a fake reflection of the surroundings onto a model based on the viewing angle.

Some get layered on top of e.g. a diffuse texture, and have an alpha channel for their layer-transparency.

Depending on the shader, these have 3 different layouts:

Cubemap

chr_sonic_white_ref.dds from Sonic Unleashed

The most detailed, and probably best known type of reflection map. Uses 6 square areas, one for each side of a cube, to represent reflections from each axis.

Spherical environment map

ghz_obj_kk1_giant_batabata_body_ref.dds from Sonic Generations

A camera rotating around Suzanne with a spherical environment map

The cheapest type of reflection, which always directly faces the camera.

Also known as MatCap textures.

Dual paraboloid environment map

ghz_metal_yy1_sky_ref.dds from Sonic Generations

Effectively a full skybox composed of 2 spherical environment maps that cover the front and back of an environment.

Covers the same area as a cubemap but with less detail.

Emission

Texture overview
File Suffix	_ems, _lum
Composition	Color
Recommended encoding	BC1_UNORM

boss_timeeater_light_ems_HD.dds from Sonic Generations

Emission textures make parts of a model emit light.

Specular

Texture overview
File Suffix	_spc
Composition	RGBA
Recommended encoding	BC3_UNORM

Specular textures contain 2 different maps:

• The blinn phong lighting specular color in the RGB channels
• The environment map (reflection) influence in the alpha channel

The color component of chr_sonic_body01_spc_HD.dds from Sonic Generations

The alpha component of chr_sonic_body01_spc_HD.dds from Sonic Generations

Gloss

Texture overview
File Suffix	_pow
Composition	Grayscale
Recommended encoding	BC1_UNORM

ghz_rock_sk1_wall01_pow.dds from Sonic Generations

Gloss textures determine the blinn phong lighting specular power.

Note

Almost every Hedgehog Engine 1 game calculates the gloss factor differently, which may cause the same gloss texture to look different in each game.

Normal Map

Texture overview
File Suffix	_nrm (rarely _norm, _nor, _nml)
Composition	Color
Recommended encoding	BC1_UNORM

ghz_rock_sk1_wall01_nrm.dds from Sonic Generations

Normal map textures are used for faking bumps and dents on a model to affect lighting, falloff, environment maps and similar.

See normal mapping for reference.

Note

Compared to blender, the green channel is inverted. (HEIO corrects this on import/export)