Hi, All
Relative motion of output is needed in Weston compositor or others. For
example, plugin a monitor, you want move it above or leftof or rightof or below
others.
More details about this motion algorithm will be shown in the email. Before
that, I mention one point, I don't refer any code from others including
xserver. My idea is based on the current Weston compositor design and
statistics. It is original for Weston compositor. At the same time, when I
implemented it, I try to make parameters to be general. If possible, make it
common instead of only in randr protocol.
Weston movement algorithm
If only support one line layout. For example, all vertical or all horizontal,
it is very easy to implement. But if we want support both at the same time, it
will be more complex instead of 1+1=2. Currently in Weston compositor, only
horizontal is supported. Compositor uses output_list to make it happen.
Here are the summary of motion properties.
1) It is similar with binary tree. Here are some related features. Every
node is one output.
a. Every node have one parent at most, also the parent maybe from
vertical, maybe from horizontal(it is different with binary tree). But never
has two parents. I will not explain why, you can use 4 outputs to do more
movement, and you can find this.
b. Every node have two children at most. One is for vertical, another is
for horizontal.
c. The tree will link all outputs, if you find some output is not in
link, that means link is lost. So when you plugin or output, you need make the
link complete. When scan Weston.ini configure, you need to organize the tree
following this algorithm.
d. Only one start point(root) exists whose coordinate is x=0 and y=0).
From that, you could find all other outputs and position them from left up most
to right down most.
e. Every branch from the main branch will never cross each other.
2) The tree is double linked.
3) The only have-to interrupt is when one node is deleted, which child
takes its place? Currently I force its horizontal child will take its place.
By the way, I list some statistics. Maybe you could find some interesting why
I post more effort on this algorithm. Layout means the final result of all
outputs' position.
Output_number Possible_Layout_number One_line_possbile_layout_number
1 1
1
2 2x2=4 (2=2x1) 2
3 5x6=30 (6=3x2x1) 6
4 14x24=336 (24=4x3x2x1) 24
You could find that, if we have 4 outputs, there are 14x24=336 possible layout
types. So the algorithm has to be designed as complete instead of only for 2,
or 3, or less. It should be designed for more. For example, supposed 500, 1000
outputs. Yes, it is in theory. But the algorithm must be that. I enumerate them
based on the movement and get the possible layouts. For example, when you have
4 outputs, even if they are in one line, there are 4x3x2x1=24 layouts.
Algorithm Implementation:
To implement this algorithm, more links have to be added for output. I add
vlink and hlink into output structure. Currently I implemented it in randr
protocol (will be posted in next version of Weston randr protocol)
With that features above, two links(vlink and hlink) should be added into
current output structure and the tree should be set up. (This will not affect
the usage of original list in output). More patches will be needed.
1) Initialization (auto found outputs and link them together)
2) Dynamic plugin and out.
3) If Weston.ini supports the layout, it should work with the algorithm.
4) Randr protocol
Important:
Currently the algorithm is implemented in randr protocol. But I want to move it
into common code instead of only randr protocol. I am not sure if it is right
and where to put algorithm code. I need agreement and discussion for that. If
no permission, I will let it in randr protocol (create another structure for
output, plus vlink and hlink).
Thanks
Regards
Quanxian Wang
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