'Re: Mirroring of the canvas'

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List: kde-kimageshop
Subject: Re: Mirroring of the canvas
From: Dmitry Kazakov <dimula73 () gmail ! com>
Date: 2010-03-24 21:16:30
Message-ID: ae32c1ef1003241416r38b7b185m5705edc07efdd803 () mail ! gmail ! com
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We have four coordinate systems:
1) image
2) viewport - scaled image coordinates (takes into account zoom-level and
image resolution)
3) widget ~ viewport transalted on "origin"
4) canvas ~ widget translated on "offset"

I'm very unsure about 3 and 4. What do they do actually? And why can't we
join both translations?

As for mirroring, i think all the translation between 1<->2 should be moved
into KisCanvas2, then you need to change only two functions and a flip flag
to get mirroring.

On Wed, Mar 24, 2010 at 10:30 PM, LukasT.dev@gmail.com <lukast.dev@gmail.com
> wrote:

> Hello,
>
> I'm trying to implement the mirroring of the canvas. It is a feature where
> we
> mirror the projection of the canvas instead of the mirroring the device
> when
> you want to see mirrored image of your paint. Similar feature is in
> mypaint.
>
> I started with mirroring the events. There are some coordinate systems in
> canvas. First one is widget space, it is possition of the input device in
> widget pixels. Then there is document space, so when you paint, the event
> from
> the widget is converted by few function calls to document coordinates.
>
> First the coordinates are translated by scrolling offset (when you move
> with
> slider in bigger zoom ) and by document origin (it is the distance from the
> canvas top left corner to image top left corner). Then the coordinates
> are transformed to document coordinates with zoom.
>
> I mirror the coordinates on document level, that means that when you draw
> stroke, the document is updated in the mirrored part. Document adds the
> "dirty
> rects on document level" so the projection is computed properly because so
> far
> projection does not know about mirroring.
>
> Next step was to mirror the canvas. I mirrored the projection by QPainter
> as Cyrille suggested using transformation like scale(-1,1) and
> translate(width,0)
>
> Now the problems started to show  up. The projection with mirrored canvas
> is
> not updated properly. So I started to investigate.
> In KisCanvas2::updateCanvasProjection I tried to mirror the vRect
> rectangle.
> The rc rectangle update the projection and the vRect is responsible to for
> proper updates calls.
>
> So far I have these problems:
> the canvas is not updated properly, I mirrored the vRect like this
> vRect = QRect(image()->width() - vRect.x()
> vRect.width(),vRect.top(),vRect.width(), vRect.height());
>
> but that is not correct. The canvas is erased in QRect
> KisPrescaledProjection::preScale(const QRect & rc)
>
>
> If I call just update(), when the whole canvas is updated, it is correct.
> What I miss there?
>
> Question: how to solve it? I don't know much about projection even I spent
> a
> lot of time looking at the code. Dmitry, what do you think I need to do?
> Is it correct to mirror the QPainter or should we mirror on the projection
> level? If so, what has to be mirrored?
>
> Another problem. When we zoom and scroll vertically, part of the image is
> erased. It seems that when we mirror the image, the hidden part because
> actually visible and in the projection it is represented by transparent
> pixel.
> Is that what is happening? Any hints where and how to fix it?
>
> Here is the patch I have for now
> http://valdyas.org/~lukast/mirroring.patch<http://valdyas.org/%7Elukast/mirroring.patch>
> _______________________________________________
> kimageshop mailing list
> kimageshop@kde.org
> https://mail.kde.org/mailman/listinfo/kimageshop
>

-- 
Dmitry Kazakov

[Attachment #5 (text/html)]

We have four coordinate systems: 1) image 2) viewport - scaled image \
coordinates (takes into account zoom-level and image resolution) 3) widget ~ \
viewport transalted on &quot;origin&quot; 4) canvas ~ widget translated on \
&quot;offset&quot; I&#39;m very unsure about 3 and 4. What do they do \
actually? And why can&#39;t we join both translations? As for mirroring, i \
think all the translation between 1&lt;-&gt;2 should be moved into KisCanvas2, then \
you need to change only two functions and a flip flag to get mirroring. <div \
class="gmail_quote">On Wed, Mar 24, 2010 at 10:30 PM, <a \
href="mailto:LukasT.dev@gmail.com">LukasT.dev@gmail.com</a> &lt;<a \
href="mailto:lukast.dev@gmail.com">lukast.dev@gmail.com</a>&gt; wrote: \
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); \
margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hello, 
I&#39;m trying to implement the mirroring of the canvas. It is a feature where we 
mirror the projection of the canvas instead of the mirroring the device when 
you want to see mirrored image of your paint. Similar feature is in mypaint. 
 
I started with mirroring the events. There are some coordinate systems in 
canvas. First one is widget space, it is possition of the input device in 
widget pixels. Then there is document space, so when you paint, the event from 
the widget is converted by few function calls to document coordinates. 
 
First the coordinates are translated by scrolling offset (when you move with 
slider in bigger zoom ) and by document origin (it is the distance from the 
canvas top left corner to image top left corner). Then the coordinates 
are transformed to document coordinates with zoom. 
 
I mirror the coordinates on document level, that means that when you draw 
stroke, the document is updated in the mirrored part. Document adds the \
&quot;dirty rects on document level&quot; so the projection is computed properly \
because so far projection does not know about mirroring. 
 
Next step was to mirror the canvas. I mirrored the projection by QPainter 
as Cyrille suggested using transformation like scale(-1,1) and 
translate(width,0) 
 
Now the problems started to show up. The projection with mirrored canvas is 
not updated properly. So I started to investigate. 
In KisCanvas2::updateCanvasProjection I tried to mirror the vRect rectangle. 
The rc rectangle update the projection and the vRect is responsible to for 
proper updates calls. 
 
So far I have these problems: 
the canvas is not updated properly, I mirrored the vRect like this 
vRect = QRect(image()-&gt;width() - vRect.x() 
vRect.width(),vRect.top(),vRect.width(), vRect.height()); 
 
but that is not correct. The canvas is erased in QRect 
KisPrescaledProjection::preScale(const QRect &amp; rc) 
 
 
If I call just update(), when the whole canvas is updated, it is correct. 
What I miss there? 
 
Question: how to solve it? I don&#39;t know much about projection even I spent a 
lot of time looking at the code. Dmitry, what do you think I need to do? 
Is it correct to mirror the QPainter or should we mirror on the projection 
level? If so, what has to be mirrored? 
 
Another problem. When we zoom and scroll vertically, part of the image is 
erased. It seems that when we mirror the image, the hidden part because 
actually visible and in the projection it is represented by transparent pixel. 
Is that what is happening? Any hints where and how to fix it? 
 
Here is the patch I have for now 
<a href="http://valdyas.org/%7Elukast/mirroring.patch" \
target="_blank">http://valdyas.org/~lukast/mirroring.patch</a> \
_______________________________________________ kimageshop mailing list 
<a href="mailto:kimageshop@kde.org">kimageshop@kde.org</a> 
<a href="https://mail.kde.org/mailman/listinfo/kimageshop" \
target="_blank">https://mail.kde.org/mailman/listinfo/kimageshop</a> \
</blockquote></div> -- Dmitry Kazakov

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