9b55f1c12b
We're in 2022 now, and HTTPS is available in a lot more places in the past. Let's upgrade some links, to protect the privacy of our readers. The links that are left either don't support HTTPS, or are simply dead and needs to be updated anyway. That's besides the scope of this merge-request, so I'm leaving that for someone else. Reviewed-by: David Heidelberg <david.heidelberg@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19492>
67 lines
2.7 KiB
ReStructuredText
67 lines
2.7 KiB
ReStructuredText
Formats in gallium
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==================
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Gallium format names mostly follow D3D10 conventions, with some extensions.
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Format names like XnYnZnWn have the X component in the lowest-address n bits
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and the W component in the highest-address n bits; for B8G8R8A8, byte 0 is
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blue and byte 3 is alpha. Note that platform endianness is not considered
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in this definition. In C::
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struct x8y8z8w8 { uint8_t x, y, z, w; };
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Format aliases like XYZWstrq are (s+t+r+q)-bit integers in host endianness,
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with the X component in the s least-significant bits of the integer. In C::
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uint32_t xyzw8888 = (x << 0) | (y << 8) | (z << 16) | (w << 24);
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Format suffixes affect the interpretation of the channel:
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- ``SINT``: N bit signed integer [-2^(N-1) ... 2^(N-1) - 1]
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- ``SNORM``: N bit signed integer normalized to [-1 ... 1]
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- ``SSCALED``: N bit signed integer [-2^(N-1) ... 2^(N-1) - 1]
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- ``FIXED``: Signed fixed point integer, (N/2 - 1) bits of mantissa
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- ``FLOAT``: N bit IEEE754 float
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- ``NORM``: Normalized integers, signed or unsigned per channel
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- ``UINT``: N bit unsigned integer [0 ... 2^N - 1]
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- ``UNORM``: N bit unsigned integer normalized to [0 ... 1]
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- ``USCALED``: N bit unsigned integer [0 ... 2^N - 1]
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The difference between ``SINT`` and ``SSCALED`` is that the former are pure
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integers in shaders, while the latter are floats; likewise for ``UINT`` versus
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``USCALED``.
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There are two exceptions for ``FLOAT``. ``R9G9B9E5_FLOAT`` is nine bits
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each of red green and blue mantissa, with a shared five bit exponent.
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``R11G11B10_FLOAT`` is five bits of exponent and five or six bits of mantissa
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for each color channel.
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For the ``NORM`` suffix, the signedness of each channel is indicated with an
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S or U after the number of channel bits, as in ``R5SG5SB6U_NORM``.
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The ``SRGB`` suffix is like ``UNORM`` in range, but in the sRGB colorspace.
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Compressed formats are named first by the compression format string (``DXT1``,
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``ETC1``, etc), followed by a format-specific subtype. Refer to the
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appropriate compression spec for details.
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Formats used in video playback are named by their FOURCC code.
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Format names with an embedded underscore are subsampled. ``R8G8_B8G8`` is a
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single 32-bit block of two pixels, where the R and B values are repeated in
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both pixels.
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Index buffers do not have a natural format in Gallium structures. For purposes
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of ``is_format_supported`` queries, the formats ``R8_UINT``, ``R16_UINT``, and
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``R32_UINT`` are used with ``PIPE_BIND_INDEX_BUFFER`` for 8-bit, 16-bit, and
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32-bit index buffers respectively.
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References
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----------
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DirectX Graphics Infrastructure documentation on DXGI_FORMAT enum:
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https://msdn.microsoft.com/en-us/library/windows/desktop/bb173059%28v=vs.85%29.aspx
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FOURCC codes for YUV formats:
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http://www.fourcc.org/yuv.php
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