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88 lines
2.3 KiB
Markdown
88 lines
2.3 KiB
Markdown
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# tga_encoder
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A TGA Encoder written in Lua without the use of external Libraries.
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Created by fleckenstein for MineClone2, then improved by erlehmann.
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May be used as a Minetest mod.
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See `examples.lua` for example code and usage hints.
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## Use Cases for `tga_encoder`
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### Encoding Textures for Editing
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TGA images of types 1/2/3 consist of header data followed by a pixel array.
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This makes it trivial to parse TGA files – and even edit pixels in-place.
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No checksums need to be updated on any kind of in-place texture editing.
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**Tip**: When storing an editable image in item meta, use zlib compression.
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### Legacy Minetest Texture Encoding
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Minetest 5.4 did not include `minetest.encode_png()` (or any equvivalent).
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Since `tga_encoder` is written in pure Lua, it does not need engine support.
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**Tip:** Look at `examples.lua` and the Minetest mod `mcl_maps` for guidance.
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### Advanced Texture Format Control
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The function `minetest.encode_png()` always encodes images as 32bpp RGBA.
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`tga_encoder` allows saving images as grayscale, 16bpp RGBA and 24bpp RGB.
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For generating maps from terrain, color-mapped formats can be more useful.
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### Encoding Very Small Textures
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Images of size 8×8 or below are often smaller than an equivalent PNG file.
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Note that on many filesystems files use at least 4096 bytes (i.e. 64×64).
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Therefore, saving bytes on files up to a few 100 bytes is often useless.
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### Encoding Reference Textures
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TGA is a simple format, which makes it easy to create reference textures.
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Using a hex editor, one can trivially see how all the pixels are stored.
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## Supported Image Types
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For all types, images are encoded in a fast single pass (i.e. append-only).
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### Color-Mapped Images (Type 1)
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These images contain a palette, followed by pixel data.
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* `A1R5G5B5` (8bpp RGB)
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* `B8G8R8` (8bpp RGB)
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* `B8G8R8A8` (8bpp RGBA)
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### True-Color Images (Type 2)
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These images contain uncompressed RGB(A) pixel data.
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* `A1R5G5B5` (16bpp RGBA)
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* `B8G8R8` (24bpp RGB)
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* `B8G8R8A8` (32bpp RGBA)
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### Grayscale Images (Type 3)
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* `Y8` (8bpp grayscale)
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### Run-Length Encoded (RLE), True-Color Images (Type 10)
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These images contain compressed RGB(A) pixel data.
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* `A1R5G5B5` (16bpp RGBA)
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* `B8G8R8` (24bpp RGB)
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* `B8G8R8A8` (32bpp RGBA)
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## TODO
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* Actually support `R8G8B8A8` input for `A1R5G5B5` output
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* Add both zoomable and explorable maps to `mcl_maps`.
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