mirror of https://github.com/20kdc/OC-KittenOS.git
53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
# KTC1 Specification
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KittenOS Texture Compression 1 is an image compression format that, while not
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size-optimized or performance-optimized for OC screens, is optimized for
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streaming from disk, and always produces precise results.
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KTC1's concepts are "inspired by" ETC1, and it was conceived after evaluating
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ETC1 for use in KittenOS NEO. ETC1, however, is not optimally fit for
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OpenComputers rendering, and thus KTC1 was created to provide an equal-size
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solution that better fit these requirements.
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A 256-colour palette is assumed, and it is assumed that the palette is provided
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outside of KTC1's context.
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A KTC1 block is one OpenComputers character (2x4 pixels), and is 4 bytes long.
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The format amounts to a foreground palette index, a background palette index,
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and a Unicode character index in the Basic Multilingual Plane.
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The unicode character is displayed with the given colours at the position of the
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block.
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The renderer does not get more complicated when more blocks are involved.
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Simply put, blocks that are overlapped by a previous wide character are to be
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totally ignored.
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The size of this format is equivalent to 4-bit indexed data and to ETC1.
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For standardization's sake, the container format for KTC1 has an 8-byte header:
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"OC" followed by two 16-bit big-endian unsigned integers, for width
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and height in blocks, the bytes-per-block count for this format (4) as
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an unsigned byte, and the amount of "comment" bytes that go after the image,
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as another unsigned byte.
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Example image, showing a 4x4 white "A" on black, with a standard text
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black "A" on white underneath:
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4F 43 00 02 00 02 04 00
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FF 00 28 6E FF 00 28 B5
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00 FF 00 41 00 FF 00 00
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## Additional Notes
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A KTC1 file is theoretically a "lossless" screenshot under the limits of the
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OpenComputers system assuming the palette is correct.
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The Basic Multilingual Plane access allows mixing images and text inside a
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KTC1 file, and covers all characters that OpenComputers supports.
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This makes KTC1 an interesting option for use as a mixed text/image interchange
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format between applications.
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