VoxeLibre/mods/CORE/tga_encoder/README.md

tga_encoder

A TGA Encoder written in Lua without the use of external Libraries.

Created by fleckenstein for MineClone2, then improved by erlehmann.

May be used as a Minetest mod.

See examples.lua for example code and usage hints.

Use Cases for tga_encoder

Encoding Textures for Editing

TGA images of types 1/2/3 consist of header data followed by a pixel array.

This makes it trivial to parse TGA files – and even edit pixels in-place.

No checksums need to be updated on any kind of in-place texture editing.

Tip: When storing an editable image in item meta, use zlib compression.

Legacy Minetest Texture Encoding

Minetest 5.4 did not include minetest.encode_png() (or any equvivalent).

Since tga_encoder is written in pure Lua, it does not need engine support.

Tip: Look at examples.lua and the Minetest mod mcl_maps for guidance.

Advanced Texture Format Control

The function minetest.encode_png() always encodes images as 32bpp RGBA.

tga_encoder allows saving images as grayscale, 16bpp RGBA and 24bpp RGB.

For generating maps from terrain, color-mapped formats can be more useful.

Encoding Very Small Textures

Images of size 8×8 or below are often smaller than an equivalent PNG file.

Note that on many filesystems files use at least 4096 bytes (i.e. 64×64).

Therefore, saving bytes on files up to a few 100 bytes is often useless.

Encoding Reference Textures

TGA is a simple format, which makes it easy to create reference textures.

Using a hex editor, one can trivially see how all the pixels are stored.

Supported Image Types

For all types, images are encoded in a fast single pass (i.e. append-only).

Color-Mapped Images (Type 1)

These images contain a palette, followed by pixel data.

• A1R5G5B5 (8bpp RGB)
• B8G8R8 (8bpp RGB)
• B8G8R8A8 (8bpp RGBA)

True-Color Images (Type 2)

These images contain uncompressed RGB(A) pixel data.

• A1R5G5B5 (16bpp RGBA)
• B8G8R8 (24bpp RGB)
• B8G8R8A8 (32bpp RGBA)

Grayscale Images (Type 3)

• Y8 (8bpp grayscale)

Run-Length Encoded (RLE), True-Color Images (Type 10)

These images contain compressed RGB(A) pixel data.

• A1R5G5B5 (16bpp RGBA)
• B8G8R8 (24bpp RGB)
• B8G8R8A8 (32bpp RGBA)

TODO

• Actually support R8G8B8A8 input for A1R5G5B5 output
• Add both zoomable and explorable maps to mcl_maps.