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wayland: Add a giant doc comment explaining "fake root" coordinate space

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This commit is contained in:
Jasper St. Pierre
2014-03-17 15:25:23 -04:00
parent 92833a0b82
commit 494e253e47
1 changed files with 38 additions and 5 deletions
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43
gdk/wayland/gdkwindow-wayland.c
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@ -1060,10 +1060,43 @@ static const struct xdg_popup_listener xdg_popup_listener = {
xdg_popup_done,
};
/**
* gdk_wayland_window_get_fake_root_coords:
* @window: A #GdkWindow
* @x_out: (out): The X offset of this window
* @y_out: (out): The Y offset of this window
*
* Wayland does not have a global coordinate space shared between
* surfaces. In fact, for regular toplevels, we have no idea where
* our surfaces are positioned, relatively.
*
* However, there are some cases like popups and subsurfaces where
* we do have some amount of control over the placement of our
* window, and we can semi-accurately control the x/y position of
* these windows, if they are relative to another surface.
*
* GTK+ loves to position "relative" popups like menus in root
* window coordinates, since it was built for display servers that
* have queryable absolute coordinate spaces. In these cases, GTK+
* might ask for the root coordinates of a widget window, add a
* few values, and then call gdk_window_move() with that absolute
* value.
*
* In Wayland, we have to "reverse-engineer" this use, and figure
* out the root coordinates from the relative position, and the
* relative position from the root coordinates.
*
* We invent a coordinate space called the "fake root coordinate"
* space in which a toplevel is always at 0,0, and all popups are
* relative to that space.
*
* gdk_wayland_window_get_fake_root_coords() gives you the
* position of a #GdkWindow in "fake root" coordinates.
*/
static void
gdk_wayland_window_offset (GdkWindow *window,
gint *x_out,
gint *y_out)
gdk_wayland_window_get_fake_root_coords (GdkWindow *window,
gint *x_out,
gint *y_out)
{
GdkWindowImplWayland *impl, *parent_impl;
GdkWindow *parent_window;
@ -1107,7 +1140,7 @@ gdk_wayland_window_create_xdg_popup (GdkWindow *window,
device = wl_seat_get_user_data (seat);
gdk_wayland_window_offset (parent, &parent_x, &parent_y);
gdk_wayland_window_get_fake_root_coords (parent, &parent_x, &parent_y);
x = window->x - parent_x;
y = window->y - parent_y;
@ -1394,7 +1427,7 @@ gdk_window_wayland_get_root_coords (GdkWindow *window,
{
gint x_offset, y_offset;
gdk_wayland_window_offset (window, &x_offset, &y_offset);
gdk_wayland_window_get_fake_root_coords (window, &x_offset, &y_offset);
if (root_x)
*root_x = x_offset + x;