docs: add 'Texture Settings'

docs/level_editor/index.rst

@@ -15,3 +15,4 @@ Console.
 
 	level_editor
 	level_viewport
+	texture_settings

docs/level_editor/texture_settings.rst

@@ -0,0 +1,76 @@
+================
+Texture Settings
+================
+
+The Texture Settings dialog lets you customize how Crown processes a texture
+for each target platform. To open it, double-click a texture in the
+:ref:`Project Browser`; Crown will display a dialog similar to this:
+
+.. image:: images/texture_settings_dialog.png
+
+Overview
+--------
+
+On the left, the ``Target Platform`` list shows the platforms you can
+configure. Select one or more platforms to edit their settings
+simultaneously. Use ``Left Ctrl`` to select or deselect multiple entries.
+
+After selecting platforms, the settings on the right update to reflect the
+current values. If the selected platforms have different values for a given
+option, a dash symbol (—) appears to indicate the inconsistency:
+
+.. image:: images/texture_settings_inconsistent_format.svg
+
+Output
+------
+
+Output settings control how Crown processes the source image into GPU-ready
+assets. These settings are applied per platform so you can accommodate each
+platform's performance and form-factor constraints.
+
+Format
+~~~~~~
+
+Choose the output format appropriate for the texture type and platform:
+
+* ``BC1``: RGB color with 1-bit alpha; good for opaque color maps.
+* ``BC2``: RGB color with 4-bits alpha.
+* ``BC3``: RGB color with full alpha.
+* ``BC4``: Single-channel (grayscale); useful for heightmaps, font atlases etc.
+* ``BC5``: Two-channel BC4 useful for tangent-space normal maps.
+* ``PTC14``: RGB compressed format.
+* ``RGB8``: Uncompressed RGB (8-bits per channel).
+* ``RGBA8``: Uncompressed RGBA (8-bits per channel).
+
+For a technical reference on BCn formats, see `Understanding BCn Texture Compression Formats <https://web.archive.org/web/20260120185114/https://www.reedbeta.com/blog/understanding-bcn-texture-compression-formats/>`_.
+
+Mip-mapping
+~~~~~~~~~~~
+
+Control mipmap generation with these options:
+
+* ``Generate Mips``: enable or disable automatic mipmap generation.
+* ``Skip Smallest Mips``: skip generation of the N smallest mip levels to save space.
+
+Other flags
+~~~~~~~~~~~
+
+* ``Normal Map``: mark the texture as a normal map. This implies linear color
+  processing.
+* ``Linear``: treat the source as linear data. By default textures are
+  interpreted as sRGB and are converted to linear space during processing;
+  enable ``Linear`` for data textures such as normal maps, LUTs etc.
+* ``Premultiply Alpha`` - premultiply RGB by alpha before encoding. See
+  `here
+  <https://web.archive.org/web/20260110150156/https://shawnhargreaves.com/blog/premultiplied-alpha.html>`_
+  and `here
+  <https://web.archive.org/web/20260103191804/https://shawnhargreaves.com/blog/premultiplied-alpha-and-image-composition.html>`_
+  for details.
+
+Saving changes
+--------------
+
+When you are finished, click the ``Save & Reload`` button at the top right.
+Crown saves the ``.texture`` resource, compiles it for the affected
+platforms, and reloads the texture in all viewports and in the running game
+if any.