kicad-developers team mailing list archive

[Maciej Sumiński <maciej.suminski@xxxxxxx>]

To make it easier to follow the drawing routines, it is good to go in 
that order:
common/drawpanel_gal.cpp:119 (onPaint()) - OnPaint event handler
common/view/view.cpp:766 (Redraw()) - Chooses the area that has to be 
redrawn
common/view/view.cpp:591 (redrawRect()) - Iterates through layers sorted 
by their renderingOrder and checks if a layer should be redrawn. If it 
is the case, then there is a visitor (drawItem) that collects VIEW_ITEMs 
from R-Tree associated with the given layer and then performs actual 
drawing. If a VIEW_ITEM was cached - then it simply redraws a group, 
otherwise it creates a group and caches it.
Groups are handled by rendering backends and are identified only by 
their number (think of it as a handle) and there is a 1-to-1 relation 
between group id and VIEW_ITEM/layer combination.

On 11/01/2013 05:06 PM, Lorenzo Marcantonio wrote:
> Another thing that's not clear to me in the GAL mechanism.
> VIEW::draw, if I got correctly the algorithm should go like this:
>
> - Ask the view for the needed GAL_LAYER_NUMs
> - Depth sort them for cairo (and probably for correct GL blending)
> - For each layer in sorted order
>    - Set the Z depth
>    - Draw the object in question
>
> My question is this: the m_layers member is a set which is most probably
> accessed by GAL_LAYER_NUM (example: VIEW::SetLayerVisible); the members
> of the set are of the internal VIEW::VIEW_LAYER struct type (which
> contains obviously useful stuff).
>
> However, the call
>
> m_gal->SetLayerDepth( m_layers.at( i ).renderingOrder );
>
> uses as index (i.e. as a GAL_LAYER_NUM, if I got it right) the i index,
> which is simply the progressive index in the sorted array of
> GAL_LAYER_NUM to be drawn. Wouldn't that be:
>
> m_gal->SetLayerDepth( m_layers.at( layers[i] ).renderingOrder );
>
> (layers is the sorted draw order)
>
> ? Otherwise I can't guess how should it work (especially the type of
> m_layers...)

The draw() routine you are asking about is only used when drawing a 
VIEW_GROUP object. Its purpose is to hold a bunch of VIEW_ITEMs together 
(do not mix it with group identifiers used by rendering backends). 
Probably I should find another name for that to avoid confusion.
VIEW_GROUPs are particularly useful when drawing on the overlay layer 
(destined for drawing temporary objects) and in that case you may need 
to draw a single item layer by layer rather than drawing layer by layer, 
but using all items.
For usual drawing of items, you should have a look at draw():607 - this 
is where caching VIEW_ITEMs/redrawing groups happen.

Regards,
Orson