Re: GTK+3 - A common event handler - Gone OT into cairo and draw territory

[Donn <donn ingle gmail com>]

On 27/05/2013 09:44, Bernhard Schuster wrote:
> Store the matrix, convert the mouse pointer to canvas space (or
> polygonspace), not the other way round.
Can you give me some sample code (pseudo or whatever)?

Once in the draw() handler, I can use the Context to get the matrix 
(somehow - I'd look into cairo

> >  The device to user and back stuff.
> > I don't know how to get the user_space without the Cairo Context and
> > this comes around to the catch-22 again: You only get a Context in the
> > draw() signal handler.
> >
> >
> >
> > > whole thing also depends on your backend. If you got a decent (
> > > OpenGL 2.1 or newer ) video card it is not really sane to calculate
> > > dirty regions and redraw them (especially if you got a lot of items
> > > floating/hanging around).
> > I'm not sure what 'backend' my GTK library is using. I'm fairly sure
> > it's not drawing Cairo paths and fills directly into GL - I reckon it's
> > still CPU bound and it's filling memory arrays which are then being
> > handed-down to the lower voodoo which mysteriously gets it to the
> > screen. i.e. it's texture maps onto GL rectangles managed by Unity (I'm
> > on ubuntu atm)
> If you can not be sure what your target devices have as backend (not to
> even speak of implementation specific stuff) set a lower-border and
> develope against that (i.e. software rendering)
>
> > > > The thing is - *if* the canvas has *not* changed, *but* I have a
> > > > tool or icon on the topmost layer that moves (I call it a sprite)
> > > > by a few pixels, then it makes more sense to do a small blit of
> > > > the old background and draw the sprite in a new position - rather
> > > > than drawing all my canvas objects again just so I can draw the
> > > > sprite in a new position.
> > > That means you need to walk your tree, check all items bounding
> > > boxes and redraw all which intersect with the boundingbox of the item
> > > moved (in the old and new position, otherwise you'd get artifacts)
> > I see what you mean. But how?
> ‘9’
> Sorry, you will have to figure that out on your own - I am not sure that
> it is possible at all - my familiarity with cairo is limited to a quite
> small subset of API calls (mostly polygon and matrix stuff, nothing
> blitting related (yet)).
>
> >  It's really a job for a block-copy kind of blit thing. I have asked
> > over on the Cairo list for such help, but there's little response. I
> > have been told to look into patterns and surfaces - so that's where I'm
> > heading. Slowly.
> >
> >
> > * Picture:
> >  A blue sky gradienting to white. A bunch of cloud images superimposed,
> > their alphas show the background. The clouds stack above each other -
> > many layers. They move left to right, some the other way.
> > There's an animated glowing Sun that rises behind them but in-front of
> > the gradient sky. Winter leaves blow in path-following spirals in the
> > foreground.
> > We pause the animation and are editing. A small 32x32 eyeball icon
> > appears at my mouse when I hit space. It intersects with:
> > 1. a bit of the leaf vector - which is itself a group of many smaller
> > shapes and fills to form the leaf.
> > 2. several layers of bits of clouds
> > 3. some section of the sun -- also a group of child shapes. For e.g.
> > the 'rays' would be triangles repeated under a rotation transform.
> > 3. some section of the gradient sky.
>
> If your clouds move you got some kind of clocking don't you? If so then
> just store all your events into static/global vars (yes, that's ugly -
> find a better solution - hint: user_data) and do the checks in a clocked
> interval (reminder: g_timeout_add is not very suiteable, as it is a
> "round about" timer)
>
> > > Keep trying, there is always that "reading-foreign-code" barrier -
> > > at first it sometimes looks all gibberish :)
> > Boy, you said it! I shall persevere.
> >
> >
> > > Makes somewhat sense, you are expected to pass a class instead of a
> > > bare function. You can then stuff all your data into that class, the
> > > only limitation in comparsion to C is, that your class _must_ contain
> > > the handler too.
> > And thanks for this!
>
> Good luck and keep going.
> Note: If you are going for such a complex widget - if you want to share
> it - it is usually "better" (as of everybody will be able to use it) if
> you write it in good old C.
> VALA after all compiles to C, but well .. code compiler gibberish all
> over the place.
>
> Bernhard


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