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oot/docs/assets/images.md

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Images

Images in the rom are in N64 image formats. On extraction, they are converted to png and written to extracted/VERSION/. On build, they are converted back to N64 formats and written as C arrays to .inc.c files in build/VERSION/.

The build system will also pick up images in assets/, allowing modders to add or even replace images.

PNG files have suffixes indicating how they are to be converted. For example, a gDekuStickTex.i8.png file will be converted to i8.

The valid formats are rgba32, rgba16, i4, i8, ia4, ia8, ia16, ci4 and ci8.

An optional suffix can be used to indicate the element type of the C array written out, for example .u32 in gHylianMan1ShirtTex.i8.u32.png. The valid array element types are u64 and u32. If omitted, the element type defaults to u64. u32 is only used for unaligned textures.

The tool implementing png->n64 conversion is build_from_png, using n64texconv as its backbone.

Replacing images

The contents of extracted/ are meant to hold the baserom assets and should not be modified. Instead, replacing an image can be done by creating a png file at the same relative path under assets/ as the image to replace.

For example, replacing gLinkHairTex (extracted/VERSION/assets/objects/gameplay_keep/gLinkHairTex.rgba16.png) with the texture for gHylianMan1BeardedEyeOpenTex (extracted/VERSION/assets/objects/object_ahg/gHylianMan1BeardedEyeOpenTex.ci8.tlut_gHylianMan1TLUT_u32.u32.png):

# for VERSION=gc-eu-mq-dbg

mkdir -p assets/objects/gameplay_keep/
cp \
    extracted/gc-eu-mq-dbg/assets/objects/object_ahg/gHylianMan1BeardedEyeOpenTex.ci8.tlut_gHylianMan1TLUT_u32.u32.png \
    assets/objects/gameplay_keep/gLinkHairTex.rgba16.png

# Cause make to rebuild gameplay_keep, where gLinkHairTex is
touch extracted/gc-eu-mq-dbg/assets/objects/gameplay_keep/gameplay_keep.c

make VERSION=gc-eu-mq-dbg

CI images

CI (Color Indexed) images also have a palette or TLUT (Texture Look-Up Table).

PNG images to be converted to CI formats may have a .tlut_gNameTLUT[_<u32|u64>] suffix indicating the name and element type (optional, defaults to u64) of the TLUT gNameTLUT.tlut.rgba16[.<u32|u64>].inc.c file to write the palette to.

If this suffix is omitted, the TLUT will be written to a gNameTex.tlut.rgba16.inc.c file named after the CI image.

For example without the .tlut_ suffix, gGanonHairFringeTex.ci8.png:

  • extracted to extracted/VERSION/assets/objects/object_ganon2/gGanonHairFringeTex.ci8.png
  • texture written to build/VERSION/assets/objects/object_ganon2/gGanonHairFringeTex.ci8.inc.c
  • palette written to build/VERSION/assets/objects/object_ganon2/gGanonHairFringeTex.tlut.rgba16.inc.c

For example with the .tlut_ suffix, gCowNoseTex.ci8.tlut_gCowTLUT.png:

  • extracted to extracted/gc-eu-mq-dbg/assets/objects/object_cow/gCowNoseTex.ci8.tlut_gCowTLUT.png
  • texture written to build/gc-eu-mq-dbg/assets/objects/object_cow/gCowNoseTex.ci8.tlut_gCowTLUT.inc.c
  • palette written to build/gc-eu-mq-dbg/assets/objects/object_cow/gCowTLUT.tlut.rgba16.bin

CI images with a .tlut_ suffix have a shared palette: there are several CI images using the same palette. The build system (build_from_png) will find images sharing the same palette by looking at the .tlut_ suffixes of png files in the same folder and in the corresponding assets/ folder.

In the matching case of shared palettes, all png files have the same palette, which is written out. Otherwise the images are automatically co-quantized and the resulting images and palette are written out.

Note the N64 supports CI images with IA16 palettes instead of RGBA16 palettes, but OoT doesn't have such textures. For simplicity, CI images with IA16 palettes are not supported in the build system, and all CI images are assumed to use RGBA16 palettes.

Skybox textures

Skybox textures, located in (extracted/VERSION/)assets/textures/skyboxes, are ci8 images with the additional specificity of being limited to a palette of 128 colors that can be loaded as either the first or last 128 colors of a 256-colors palette, depending on the skybox.

The build system identifies such textures with the additional "sub-format" suffix .split_lo or .split_hi right after the .ci8 suffix. split_lo corresponds to textures where the half palette is mapped to the lower half, and split_hi to the higher half.

Like for regular ci images, images are automatically converted, quantized and written within those restrictions by the build system.