GTK HID architecture

Alain, Igor2

Situation @ pcb-rnd v1.2.1

The HIDs are plug-ins, sitting in src_plugins/hid_* ; GTK2 one is called hid_gtk.

First, get an instance of the main HID structure pcb_hid_t. This structure is general enough. Nothing too entangled to GTK2 nor GTK3 there.

pcb_hid_t pcb_gui = pcb_hid_find_gui ()

Q: How GTK HID is initialized ?

A: hid_hid_gtk_init () in <hid_gtk/gtkhid-main.c>

The GUI seems to start building from ghid_do_export ()

There are 2 big structures for GTK2 GUI:

GhidGui _ghidgui, *ghidgui = &_ghidgui;

GHidPort ghid_port, *gport;

GTK3 compatibility within these 2 structures:

Table 1. GhidGui structure study (portion)
Type GTK3 compatible GTK3 replacement GTK2 compatible ?

GtkWidget

GtkObject

GObject

could be

GdkPixmap

GdkPixbuf

could be

GtkAction

deprecated

GAction (gio)

could be (not desired)

GtkActionGroup

GActionGroup

(not desired)

GtkEntry

GTimeVal

(glib)

Table 2. GHidPort structure study (portion)
Type GTK+3 compatible GTK+3 replacement GTK+2 compatible ?

GtkWidget

GdkPixmap

GdkPixbuf

could be

GdkDrawable

Cairo surface

(not desired)

GdkColor

GdkRGBA

1

GdkColormap

GdkVisual

1

1 An abstracted structure was envisioned, but abandoned due to scarce use of color objects.

Drawing primitives using GDKx

GDK2

pcb-rnd v1.2.1 is using gdk_draw functions, on an already abstracted pcb_hid_t intance of hid_gc_s structure.

Table 3. hid_gc_s structure study (portion)
Type GTK+3 compatible GTK+3 replacement GTK+2 compatible ?

GdkGC

Cairo context

could be (not desired)

Indirectly, a GdkGC needs a GdkDrawable which is also deprecated in GTK3. A good replacement is a GdkWindow. Unfortunately pcb-rnd is making more use of deprecated GdkPixmap objects than GdkWindow.

gdk_draw_line has been deprecated since GTK+ 2.22. Use cairo_line_to and cairo_stroke instead. gdk_gc_new has been deprecated since GTK+ 2.22. Use Cairo for rendering.

Cairo API needs a context:

cairo_line_to (cairo_t *cr,
               double x,
               double y);
cairo_t *
cairo_create (cairo_surface_t *target);

and then pops-up the Cairo Surface !

A cairo_surface_t represents an image, either as the destination of a drawing operation or as source when drawing onto another surface.

GDK does not wrap the cairo API, instead it allows to create cairo contexts which can be used to draw on GdkWindow. Additional functions allow use GdkRectangles with cairo and to use GdkColors, GdkRGBAs, GdkPixbufs and GdkWindows as sources for drawing operations.

GDK3

Cairo Interaction

Cairo is a graphics library that supports vector graphics and image compositing that can be used with GDK. GTK+ does all of its drawing using cairo. But I guess, it is also the case with late GDK2 !

Open GL

GdkGLContext is an object representing the platform-specific OpenGL drawing context.

Very modern GDK3

GdkDrawingContext is an object that represents the current drawing state of a GdkWindow. It's possible to use a GdkDrawingContext to draw on a GdkWindow via rendering API like Cairo or OpenGL.

Since: 3.22

Plans for pcb-rnd v1.2.2 ?

  1. What we must have:

    1. the old gtk2 HID, with pixmaps and all the existing obsolete code - for existing/old systems. We won't remove or change this, there's absolutely no reason to risk running on older systems. We probably won't remove it in any time soon, because some people love to run real OLD systems.

    2. whichever gtk HID with gl rendering; let's say gtk2+gl, because gtk2 is what we have working today. This seems to be real appealing for many users.

  2. What extras we could have and totally makes sense:

    1. the new, gtk3 HID, with Cairo for sw rendering, because as far as I understand there's no other option for sw rendering in gtk3

    2. the new, gtk3 HID with gl rendering

  3. What we could temporarily have, if it helped us on our way to previous:

    1. a temporary, hidden, development gtk2+cairo implementation so that cairo can be done in something that's already there before gtk3 happens. This must not interfere with the gdk/pixmap implementation. This must not remain for long in the repo, and must be converted into the gtk3+cairo hid ASAP.

  4. What we shouldn't have because it doesn't make much sense but increases the confusion and development/maintainance costs:

    1. a permanent, advertised gtk2+cairo HID. gtk2 works perfectly fine with existing installation and the existing code. Cairo can only add slowdown to this and introduces new build risks. Old systems don't need cairo to work. New systems will have gtk3 sooner or layer anyway. Other than a few "obsolete" marks in the manual, there's absolutely no issue with a gtk2+pixmap.