LAYER(2) LAYER(2)
NAME
lalloc, lfree, ltofront, ltoback, lcstring - graphics layers
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <libg.h>
#include <layer.h>
Layer* lalloc(Cover *c, Rectangle r)
void lfree(Layer *l)
void ltofront(Layer *l)
void ltoback(Layer *l)
void lcstring(Bitmap *b, int height, uchar *widths, uchar *msg,
int n)
DESCRIPTION
The layer library extends the functionality of the bitmap
graphics library (see graphics(2)) to overlapping indepen-
dent rectangular windows, or layers, on a single bitmap,
typically the screen. The entry points bitblt, point,
segment, string, subfontstring, and texture are overloaded
in the layer library to apply these routines equally to bit-
maps and layers. Other than lcstring, which is rarely
needed, there are no special entry points for drawing on
layers.
The data structures associated with the main type, Layer,
are defined in <layer.h>:
typedef struct Layer Layer;
typedef struct Cover Cover;
typedef enum Lvis {
Visible,
Obscured,
Invisible,
}Lvis;
struct Layer {
Bitmap; /* Bitmap.cache!=0 ==> layer */
Layer *next; /* next layer from front to back */
Cover *cover; /* layer etc. that derived this one */
int user; /* a place for the user to stick stuff */
Lvis vis; /* visibility state */
};
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LAYER(2) LAYER(2)
struct Cover {
Layer *layer; /* layer on which these are painted */
Layer *front; /* first sublayer */
Bitmap *ground; /* background texture */
};
Layers and Bitmaps are distinguished by the cache element of
their structures: cache is non-zero in a Layer. The layer
library's versions of the graphics routines listed above use
cache to decide how to implement their operations. These
functions operate on type Bitmap* but because Bitmap is
included in Layer, the C compiler will permit passing a
Layer to these routines. The routines promote the type to
Layer* if they see cache is non-zero. (Note that these
actions apply only in the layer library; although cache is
defined in Bitmaps, the standard graphics library does not
support layers.)
Lalloc allocates a new Layer to occupy Rectangle r in a
Bitmap. The argument Cover c connects the set of Layers to
a covering Bitmap. Before the first call to lalloc, c
should be allocated and initialized so c->layer is the
Bitmap on which the Layers will be drawn, c->front is zero,
c->ground is a background texture to fill the interstices
between Layers, and c->layer is textured with c->ground. It
is legal for c->layer itself to be a Layer for recursive
layering. The rectangle r may have arbitrary overlap,
including none, with c->layer->r. After calling lalloc, the
new Layer is fully visible (as far as geometry permits) on
the covering Bitmap and is cleared to all zeros.
Lfree frees the Layer l and restores the contents of its
covering Bitmap.
Ltofront makes l fully visible within its covering Bitmap.
Ltoback pushes l behind any other Layers on the same cover-
ing Bitmap. Neither function changes the x-y location of
the Layer.
Lcstring is peculiar to programs, such as 8½(1), that multi-
plex client access to the display. It acts as a feed-
through for the 's' message generated by string (see
bit(3)). B is the bitmap (or layer) and height is the height
of the font in which the string is to be drawn. Widths is
an array of character widths, indexed by font cache posi-
tion. Msg is a pointer to the string message; it contains
the header and n cache indices.
SOURCE
/sys/src/liblayer
SEE ALSO
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LAYER(2) LAYER(2)
graphics(2), bitblt(2), cachechars(2), bit(3)
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