partially update hacking-howto with an explanation of the moving code
Michael Stapelberg
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Hacking i3: How To
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==================
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Michael Stapelberg <michael+i3@stapelberg.de>
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December 2009
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February 2010
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This document is intended to be the first thing you read before looking and/or
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touching i3’s source code. It should contain all important information to help
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you understand why things are like they are. If it does not mention something
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you find necessary, please do not hesitate to contact me.
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PLEASE BEWARE THAT THIS DOCUMENT IS ONLY PARTIALLY UPDATED FOR -tree YET!
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== Window Managers
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A window manager is not necessarily needed to run X, but it is usually used in
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@ -485,6 +487,131 @@ j, k and l, like in vim (h = left, j = down, k = up, l = right). When you just
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specify the direction keys, i3 will move the focus in that direction. You can
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provide "m" or "s" before the direction to move a window respectively or snap.
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== Moving containers
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The movement code is pretty delicate. You need to consider all cases before
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making any changes or before being able to fully understand how it works.
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=== Case 1: Moving inside the same container
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The reference layout for this case is a single workspace in horizontal
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orientation with two containers on it. Focus is on the left container (1).
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[width="15%",cols="^,^"]
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|========
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| 1 | 2
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|========
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When moving the left window to the right (command +move right+), tree_move will
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look for a container with horizontal orientation and finds the parent of the
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left container, that is, the workspace. Afterwards, it runs the code branch
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commented with "the easy case": it calls TAILQ_NEXT to get the container right
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of the current one and swaps both containers.
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=== Case 2: Move a container into a split container
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The reference layout for this case is a horizontal workspace with two
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containers. The right container is a v-split with two containers. Focus is on
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the left container (1).
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[width="15%",cols="^,^"]
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|========
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1.2+^.^| 1 | 2
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| 3
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|========
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When moving to the right (command +move right+), i3 will work like in case 1
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("the easy case"). However, as the right container is not a leaf container, but
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a v-split, the left container (1) will be inserted at the right position (below
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2, assuming that 2 is focused inside the v-split) by calling +insert_con_into+.
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+insert_con_into+ detaches the container from its parent and inserts it
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before/after the given target container. Afterwards, the on_remove_child
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callback is called on the old parent container which will then be closed, if
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empty.
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Afterwards, +con_focus+ will be called to fix the focus stack and the tree will
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be flattened.
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=== Case 3: Moving to non-existant top/bottom
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Like in case 1, the reference layout for this case is a single workspace in
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horizontal orientation with two containers on it. Focus is on the left
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container:
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[width="15%",cols="^,^"]
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|========
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| 1 | 2
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|========
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This time however, the command is +move up+ or +move down+. tree_move will look
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for a container with vertical orientation. As it will not find any,
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+same_orientation+ is NULL and therefore i3 will perform a forced orientation
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change on the workspace by creating a new h-split container, moving the
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workspace contents into it and then changing the workspace orientation to
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vertical. Now it will again search for parent containers with vertical
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orientation and it will find the workspace.
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This time, the easy case code path will not be run as we are not moving inside
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the same container. Instead, +insert_con_into+ will be called with the focused
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container and the container above/below the current one (on the level of
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+same_orientation+).
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Now, +con_focus+ will be called to fix the focus stack and the tree will be
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flattened.
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=== Case 4: Moving to existant top/bottom
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The reference layout for this case is a vertical workspace with two containers.
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The bottom one is a h-split containing two containers (1 and 2). Focus is on
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the bottom left container (1).
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[width="15%",cols="^,^"]
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|========
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2+| 3
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| 1 | 2
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|========
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This case is very much like case 3, only this time the forced workspace
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orientation change does not need to be performed because the workspace already
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is in vertical orientation.
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=== Case 5: Moving in one-child h-split
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The reference layout for this case is a horizontal workspace with two
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containers having a v-split on the left side with a one-child h-split on the
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bottom. Focus is on the bottom left container (2(h)):
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[width="15%",cols="^,^"]
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|========
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| 1 1.2+^.^| 3
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| 2(h)
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|========
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In this case, +same_orientation+ will be set to the h-split container around
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the focused container. However, when trying the easy case, the next/previous
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container +swap+ will be NULL. Therefore, i3 will search again for a
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+same_orientation+ container, this time starting from the parent of the h-split
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container.
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After determining a new +same_orientation+ container (if it is NULL, the
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orientation will be force-changed), this case is equivalent to case 2 or case
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4.
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=== Case 6: Floating containers
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The reference layout for this case is a horizontal workspace with two
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containers plus one floating h-split container. Focus is on the floating
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container.
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TODO: nice illustration. table not possible?
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When moving up/down, the container needs to leave the floating container and it
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needs to be placed on the workspace (at workspace level). This is accomplished
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by calling the function +attach_to_workspace+.
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== Gotchas
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* Forgetting to call `xcb_flush(conn);` after sending a request. This usually
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