[gimp] devel-docs: information about the icon themes.

[Jehan Pagès <jehanp src gnome org>]

commit 562404f52def3fc5af2d77db74e66bdd21303d62
Author: Jehan <jehan girinstud io>
Date:   Fri Aug 5 23:43:02 2016 +0200

    devel-docs: information about the icon themes.

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+====================
+Icon themes for GIMP
+====================
+
+---------------
+Released Themes
+---------------
+
+GIMP 2.10 comes with 4 icon themes:
+
+(1) Symbolic: the default icon theme (made for dark themes).
+We follow GNOME guidelines when possible:
+https://developer.gnome.org/hig/stable/icons-and-artwork.html.en
+
+(2) Symbolic-Inverted: programmatically generated from the "Symbolic"
+icon theme by inverting colors. Icon designers should not create icons
+specifically for "Symbolic-Inverted".
+
+Note: exceptions on the icon generation can be applied.
+For instance "gimp-default-colors" and "gimp-toilet-paper" icons are not
+inverted. And "gimp-color-picker-black" is generated by inverting
+"gimp-color-picker-white" and reciprocally.
+Ask for developer help when such exceptions are needed.
+
+(3) Color: a new color icon theme, also designed with vector graphics.
+
+(4) Legacy: this icon theme which contains the old GIMP 2.8 icons. It is
+not maintained anymore and we are not expecting new icons for Legacy.
+Yet since we keep them in the source tree for now, we would accept
+updates.
+
+The Symbolic icon theme are our main target since they are considered
+better suited for graphics work (less visual distraction). Color icons
+are kept as fall-over since some users still prefer them.
+
+----------------
+Adding new icons
+----------------
+
+- Add new icons in the single SVG file inside their respective
+directories, i.e. `icons/Symbolic/symbolic-scalable.svg` for symbolic
+icons and `icons/Color/color-scalable.svg` for color icons.
+
+A single file allows easier reuse of material, and easy overview of all
+existing icons which simplifies consistent styling…
+
+- The contents of the SVG file should be organized for easy management
+and easy contribution. You can visually group similar icons, make use
+of layers, whatever is necessary for organization.
+
+- You should group all parts of a single icon into a single object and
+id this object with the icon name. For instance the object containing
+the Move Tool icon should be id-ed: "gimp-tool-move".
+
+- Make sure the object has the right expected size. A good trick is to
+group with a square of the right size, made invisible.
+
+- Export the icon as PNG and SVG into the appropriate size directory.
+
+Ideally this step should be done at build time, but we could not find
+yet a reliable way to extract icons out of the single SVG file without
+using crazy build dependencies (like Inkscape). So this is done by hand
+for the time being.
+
+- Add the icons in `icons/icon-list.mk`.
+This file is shared by all 3 maintained icon themes (Symbolic,
+Symbolic-Inverted and Color), so you must make sure that you have the
+Symbolic as well as the Color icons drawn before adding them.
+
+Pixel perfection
+----------------
+
+Even as vectorial, icons should be pixel-perfect when possible.
+Therefore the first step before making an icon is to determine which
+size it is supposed to appear at.
+If the icon could appear in several sizes:
+
+- if the sizes are multiples, just design the smaller size. The bigger
+icon will stay pixel-perfect when scaled by a multiple. So for instance,
+if you want the icon to be 12x12 and 24x24, just design the 12x12 icon.
+
+- of course, if the size difference is big enough, you may want to
+create a new version with added details, even when this is a multiple
+(i.e. 12x12 and 192x192 may be different designs). These are design
+choices.
+
+- when sizes are no multiple (i.e. 16x16 and 24x24), it is preferred to
+have 2 pixel-perfect versions.
+
+- if time is missing, creating the smaller size only is a first step
+and is acceptable.
+
+Sizes
+-----
+
+Some known sizes:
+
+- tool icons: 16x16 and 22x22.
+- dock tab icons: 16x16 and 24x24.
+- menu icons: 16x16.
+[…]
+
+-------------
+Testing icons
+-------------
+
+Icons in menus are not always shown. In particular some desktop environments
+would not show them by default, for instance GNOME. You can force them to
+show up by setting the environment variable `GIMP_ICONS_LIKE_A_BOSS`.
+
+For instance, start GIMP like this:
+
+    GIMP_ICONS_LIKE_A_BOSS=1 gimp-2.9