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().
We're going to need to allow rendering on a specific cairo_t in order to
implement fallback code paths inside GTK; this means that there will be
times when we have a transient GskRenderer instance that does not have a
GdkDrawingContext to draw on.
Instead of adding a new render() implementation for those cases and then
decide which one to use, we can remove the drawing context argument from
the virtual function itself, and allow using a NULL GdkDrawingContext
when calling gsk_renderer_render(). A later commit will add a generic
function to create a transient GskRenderer with a cairo_t attached to
it.
Renderers inside GSK will have to check whether we have access to a
GdkDrawingContext, in which case we're going to use it; or if we have
access to a cairo_t and a window.
GskRenderNode is, at its core, a write-only API; you're supposed to set
up the render nodes instead of querying them for state.
Querying render nodes is left to the GskRenderer implementation.
Add a should_propagate function for render nodes. Eventually,
this is meant to avoid creating render nodes for child widgets
that are outside the parents clip area. Since we don't have
that information available right now, just filter out nondrawable
children for now.
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.
We store the vertices in (unscaled) window coords (but the item size
is still scaled to match the texture size). Also, the
projection/model-view multiplication order is switched so that the scale
is applied at the right place.
The renderer will always use nearest-neighbor filters because it renders
at 1:1 pixel to texel ratio.
On the other hand, render nodes may be scaled, so we need to offer a way
to control the minification and magnification filters.
If we already have a GL texture we definitely don't want to use
gdk_cairo_draw_from_gl() to draw on a Cairo context if we're going
to take the Cairo surface to which we draw and put it into an OpenGL
texture.
The details of the modelview and projection matrices are only useful for
the GL renderer; there's really no point in having those details
available in the generic API — especially as the Cairo fallback renderer
cannot really set up a complex modelview or a projection matrix.
Instead of using the background as the gadget's node, we add a
non-drawing node that can be used to apply offsets; all other nodes are
children of the "box" node.
Just like we reuse texture ids with the same size we can, at the expense
of a little memory, reuse vertex buffers if they reference the same
attributes and contain the same data.
Each VAO is marked as free at the end of the frame, and if it's not
reused in the following frame, it gets dropped.
The child-transform is useful only if we also provide clipping to the
parent nodes, otherwise children will just be drawn outside of the
parent's bounds.
We'll introduce child transforms either at a higher layer, or once we
add clipping support to GskRenderNode.
This is the first example of indirect rendering involving
a box gadget. For now, we iterate the child gadgets manually,
and rely on gtk_container_propagate_render_node for the
child widgets. Eventually, we may want a better solution
here.
...and implement it for GtkCssGadget and GtkCssCustomGadget.
This allows us to decide on a per-object basis if a custom
gadget needs a render node for content or not.
The custom gadget draw function has the side effect of informing
the gadget machinery wether to draw focus or not. Bring the
draw function back, just for its boolean return value. We may
want to find a better solution for this.
I don't think this should stay in the code long-term, but it
is useful for debugging. It helped me track down some suspicious
placements of render nodes.
Give all nodes the same detail about the owner widget.
This reveals that every GtkCssCustomGadget gets a
DrawGadgetContents node, even if their draw_func is NULL.
We may want to come up with a better solution for that.
When creating the GskRenderNodes for the gadgets we should not translate
the coordinates inside the Cairo context, but we should tweak the
coordinates of the anchor point.
This is still not enough to get an appropriate rendering, as the result
is still slightly offset to the left.
