| WINDOW(3) | WINDOW(3)

NAME

| Screen, allocscreen, publicscreen, freescreen, allocwindow, bottomwindow, bottomnwindows, topwindow, topnwindows, originwindow – window management

SYNOPSIS

`#include <u.h>
#include <libc.h>
#include <draw.h>

` `typedef
struct Screen
{

| Display *display; /* display holding data */ int id; /* id of system−held Screen */ Image *image; /* unused; for reference only */ Image *fill; /* color to paint behind windows */

} Screen;

Screen* allocscreen(Image *image, Image *fill, int public)

` `Screen* publicscreen(Display *d, int id, ulong chan)

` `int freescreen(Screen *s)

` `Image* allocwindow(Screen *s, Rectangle r, int ref, int val)

` `void bottomwindow(Image *w)

` `void bottomnwindows(Image **wp, int nw)

` `void topwindow(Image *w)

` `void topnwindows(Image **wp, int nw)

` `int originwindow(Image *w, Point log, Point scr)

` `enum
{

| /* refresh methods */ Refbackup= 0, Refnone= 1, Refmesg= 2

};
`

DESCRIPTION

Windows are represented as `Images` and may be treated as regular images for all drawing operations. The routines discussed here permit the creation, deletion, and shuffling of windows, facilities that do not apply to regular images.

To create windows, it is first necessary to allocate a `Screen` data structure to gather them together. A `Screen` turns an arbitrary image into something that may have windows upon it. It is created by `allocscreen`, which takes an image upon which to place the windows (typically `display−>image`), a fill image to paint the background behind all the windows on the image, and a flag specifying whether the result should be publicly visible. If it is public, an arbitrary other program connected to the same display may acquire a pointer to the same screen by calling `publicscreen` with the `Display` pointer and the id of the published `Screen`, as well as the expected channel descriptor, as a safety check. It will usually require some out-of-band coordination for programs to share a screen profitably. `Freescreen` releases a `Screen`, although it may not actually disappear from view until all the windows upon it have also been deallocated.

Unlike `allocwindow`, `allocscreen` does not initialize the appearance of the `Screen`.

Windows are created by `allocwindow`, which takes a pointer to the `Screen` upon which to create the window, a rectangle r defining its geometry, an integer pixel value val to color the window initially, and a refresh method `ref`. The refresh methods are `Refbackup`, which provides backing store and is the method used by rio(1) for its clients; `Refnone`, which provides no refresh and is designed for temporary uses such as sweeping a display rectangle, for windows that are completely covered by other windows, and for windows that are already protected by backing store; and `Refmesg`, which causes messages to be delivered to the owner of the window when it needs to be repainted. `Refmesg` is not fully implemented.

The result of `allocwindow` is an `Image` pointer that may be treated like any other image. In particular, it is freed by calling `freeimage` (see allocimage(3)). The following functions, however, apply only to windows, not regular images.

`Bottomwindow` pushes window w to the bottom of the stack of windows on its `Screen`, perhaps obscuring it. `Topwindow` pulls window w to the top, making it fully visible on its `Screen`. (This `Screen` may itself be within a window that is not fully visible; `topwindow` will not affect the stacking of this parent window.) `Bottomnwindows` and `Topnwindows` are analogous, but push or pull a group of nw windows listed in the array wp. The order within wp is unaffected.

Each window is created as an `Image` whose `Rectangle r` corresponds to the rectangle given to `allocwindow` when it was created. Thus, a newly created window w resides on its `Screen−>image` at w`−>r` and has internal coordinates w`−>r`. Both these may be changed by a call to `originwindow`. The two `Point` arguments to `originwindow` define the upper left corner of the logical coordinate system (log) and screen position (scr). Their usage is shown in the Examples section.

Rio(1) creates its client windows with backing store, `Refbackup`. The graphics initialization routine, `initdraw` (see graphics(3)), builds a `Screen` upon this, and then allocates upon that another window indented to protect the border. That window is created `Refnone`, since the backing store created by `rio` protects its contents. That window is the one known in the library by the global name `screen` (a historic but confusing choice).

EXAMPLES

To move a window to the upper left corner of the display,

| `originwindow(w, w−>r.min, Pt(0, 0));`

To leave a window where it is on the screen but change its internal coordinate system so (0, 0) is the upper left corner of the window,

| `originwindow(w, Pt(0, 0), w−>r.min);`

After this is done, `w−>r` is translated to the origin and there will be no way to discover the actual screen position of the window unless it is recorded separately.

SOURCE

| `/usr/local/plan9/src/libdraw`

SEE ALSO

| graphics(3), draw(3), cachechars(3), draw(3)

BUGS

| The refresh method `Refmesg` should be finished.