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Re: Fwd: [PATCH 1/2] Framebuffer split

From: Michal Suchanek
Subject: Re: Fwd: [PATCH 1/2] Framebuffer split
Date: Mon, 10 Aug 2009 20:41:12 +0200

2009/8/10 Vladimir 'phcoder' Serbinenko <address@hidden>:
> On Mon, Aug 10, 2009 at 4:38 PM, Michal Suchanek<address@hidden> wrote:
>> Yes, but set_viewport works on the active target. You create an
>> offscreen target and set it as the active target and want to set the
>> viewport on it. Depending on its size this function either needlessly
>> limits you to the current screen mode or allows illegal viewport to be
>> set.
>> It simply compares apples and oranges.
> Fixed in repo. New patch is coming after testing


>> I just want the drivers not touch the render target structure so that
>> it is possible to add features to video_fb (such as framebuffer
>> rotation) later without breaking the drivers that do not use them.
>> Because it breaks encapsulation and needlessly duplicates code.
> I'm not sure that encapsulation is good in this particular case.
> Clearly the driver should take the lead and not the framebuffer
> library. Now it's coded with "library of functions" concept and
> changing concept will put strains on drivers. I don't know which
> approach is better in a long run
>>> Both pieces of code check against the current mode. It's just because
>>> vbe does most of job for us that this code is a bunch of assignments
>>> but it may be more complex. I don't see what your problem with filling
>>> render target about screen parameters is
>> Exactly that it may get more complex. You have to change the code in
>> all drivers then.
> Why? Driver just sets fields framebuf? In which cases does it need to
> be modified?
>>> Then you pass video mode info which is just a screen render target
>> Yes, without any needless redundancy.
> Passing framebuffer parameters one way or another you have redundancy
>> For that they should be able to create and use render targets but not
>> manipulate them directly.
> They do. They need to say "this render target is at ... with these parameters"
>> The mode_info is already part of the framebuffer so I only ask that
>> the driver fills in the mode_info and has a render target created from
>> that rather than creating a render target itself.
> mode_info lacks crucial data like framebuffer address.
Yes, it does.

I would like a video_fb function like
grub_video_fb_create_render_target_from_buffer(void * buffer, int
allocated, const grub_video_mode_info_t * mode_info)

>> If features are later added to the render target (such as rotation)
>> this code needs to be aware of them. However, if the structure was
>> filled out in fb_video then these new features are transparent.
> But if a driver partially accelerates rotation it needs to tell which
> buffers are rotated and which aren't. Basically we have 2 possible

Yes, and it can create them rotated or not as appropriate (and specify
that in the mode_info). If the rotation is done in hardware then it
should be transparent and the buffer is effectively non-rotated as far
as video_fb cares.

> benefits but I'm not sure which one is better. What do others think?

I am sure that for doing transparent rotation in video_fb
encapsulation is good. I can do without it or patch it in with the
rotation if I get it into working state.

The only other users of the render_target structure are drivers and
from what I have seen so far they should better be kept at good
distance from it.

However, an opinion of somebody else who looks at the graphics
subsystem would be welcome.



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