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Add some CSS node docs

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Write up some of the insights from doing the CSS node transition,
so the knowledge is not lost.
This commit is contained in:
Matthias Clasen 2015-11-19 12:55:30 -05:00
parent e2d9051f23
commit 2b5d4455b8
1 changed files with 36 additions and 0 deletions
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36
gtk/gtkcssnode.c
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@ -26,6 +26,42 @@
#include "gtksettingsprivate.h"
#include "gtktypebuiltins.h"
/*
* CSS nodes are the backbone of the GtkStyleContext implementation and
* replace the role that GtkWidgetPath played in the past. A CSS node has
* an element name and a state, and can have style classes, which is what
* is needed to determine the matching CSS selectors. CSS nodes have a
* 'visible' property, which makes it possible to temporarily 'hide' them
* from CSS matching - e.g. an invisible node will not affect :nth-child
* matching and so forth.
*
* CSS nodes are organized in a dom-like tree, and there is API to navigate
* and manipulate this tree:
* - gtk_css_node_set_parent
* - gtk_css_node_insert_before/after
* - gtk_css_node_get_parent
* - gtk_css_node_get_first/last_child
* - gtk_css_node_get_previous/next_sibling
*
* Every widget has one or more CSS nodes - the first one gets created
* automatically by GtkStyleContext. To set the name of the main node,
* call gtk_widget_class_set_css_name() in class_init. Widget implementations
* can and should add subnodes as suitable.
*
* Best practice is:
* - for permanent subnodes, create them in init(), and keep a pointer
* to the node (you don't have to keep a reference, cleanup will be
* automatic by means of the parent node getting cleaned up by the
* style context
* - for transient nodes, create/destroy them when the conditions that warrant
* their existence change.
* - keep the state of all your nodes up-to-date. This probably requires
* a state-flags-changed (and possibly direction-changed) handler, as well
* as code to update the state in other places
* - the draw function should just use gtk_style_context_save_to_node to
* 'switch' to the right node, not make any other changes to the style context
*/
/* When these change we do a full restyling. Otherwise we try to figure out
* if we need to change things. */
#define GTK_CSS_RADICAL_CHANGE (GTK_CSS_CHANGE_ID | GTK_CSS_CHANGE_NAME | GTK_CSS_CHANGE_CLASS | GTK_CSS_CHANGE_SOURCE | GTK_CSS_CHANGE_PARENT_STYLE)