While porting GTK to GskRenderer we noticed that the current fallback
code for widgets using Cairo to draw is not enough to cover all the
possible cases.
For instance, if a container widget still uses GtkWidget::draw to render
its children, and at least one of them has been ported to using render
nodes instead, the container won't know how to draw it.
For this reason we want to provide to layers above GSK the ability to
create a "fallback" renderer instance, created using a "parent"
GskRenderer instance, but using a Cairo context as the rendering target
instead of a GdkDrawingContext.
GTK will use this inside the gtk_widget_draw() implementation, if a
widget implements GtkWidgetClass.get_render_node().
Change get_render_node to return nodes that are sized to the clip
area and expect to be placed at the clip position; change
gtk_container_propagate_render_node to place child render nodes
accordingly, and change gtk_css_gadget_get_render_node to return
nodes that are sized accordingly as well.
GtkWidget.create_render_node() sets up a GskRenderNode appropriate for
rendering the contents of a widget, including its bounds,
transformation, and anchor point.
The naming is consistent with other scene graph libraries, as it
represents an additional translation transformation applied on top of
the provided transformation matrices.
We can also simplify the implementation by applying the translation when
we compute the world matrix.
We were allocating a surface thats big enough for the clip, and
we were setting the transform for that, but then GtkContainer
was overriding the transform with the one for the allocation.
Also, we were drawing at the clip position, not the allocation
position.
Render nodes need access to rendering information like scaling factors.
If we keep render nodes separate from renderers until we submit a nodes
tree for rendering we're going to have to duplicate all that information
in a way that makes the API more complicated and fuzzier on its
semantics.
By having GskRenderer create GskRenderNode instances we can tie nodes
and renderers together; since higher layers will also have access to
the renderer instance, this does not add any burden to callers.
Additionally, if memory measurements indicate that we are spending too
much time in the allocation of new render nodes, we can now easily
implement a free-list or a renderer-specific allocator without breaking
the API.
The clip rectangle may have non-zero offsets, so we need to ensure that
the GskRenderNode associated to the rendered area is translated by those
same offsets.
We need a virtual function to retrieve the GskRenderNode for each
widget, which is supposed to attach its own children's GskRenderNodes.
Additionally, we want to maintain the existing GtkWidget::draw mechanism
for widgets that do not implement get_render_node() — as well as widgets
that have handlers connected to the ::draw signal.
And replaces its usages in GtkTextView/GtkStyleContext with a hard-coded
0.04 which was the default value for cursor-aspect-ratio. Also remove
the public gtk_draw_insertion_cursor which used draw_insertion_cursor
which in turn looked up cursor-aspect-ratio
And with it, gtk_widget_get_visual() and gtk_widget_set_visual() are
gone.
We now always use the RGBA visual (if available) and otherwise fall back
to the system visual.
This was meant to be silenced unless expicitly requested but
G_ENABLE_DEBUG is defined by default unless --disable-debug is passed to
configure, so use G_ENABLE_CONSISTENCY_CHECKS instead which is only
defined if --enable-debug is explicitly passed.
If somebody decides to use gtk_widget_set_double_buffered() in the
middle of a draw() then there's the risk of calling end_draw_frame()
with an invalid pointer.
Some overeager compilers may warn about the double_buffered bit field
changing values and leading to a potentially uninitialized variable.
In order to avoid compiler warnings or crashes, we can simply store the
value of the double_buffered bit field at the beginning of the rendering
and use that instead of the actual bit field.
https://bugzilla.gnome.org/show_bug.cgi?id=771463
