NAME

Display − connection to draw device

SYNOPSIS

include"draw.m"; draw := load Draw Draw->PATH;
 
Display: adt {
    image:       ref Image;
    ones:        ref Image;
    zeros:       ref Image;
 
    allocate:    fn(dev: string):
                 ref Display;
    startrefresh:fn(d: self ref Display);
    publicscreen:fn(d: self ref Display, id: int):
                 ref Screen;
    newimage:    fn(d: self ref Display,
                 r: Rect, ldepth, repl, color: int):
                 ref Image;
    color:       fn(d: self ref Display, color: int):
                 ref Image;
    rgb:         fn(d: self ref Display, red, green, blue: int):
                 ref Image;
    open:        fn(d: self ref Display, name: string):
                 ref Image;
    readimage:   fn(d: self ref Display, fd: ref Sys->FD):
                 ref Image;
    writeimage:  fn(d: self ref Display, fd: ref Sys->FD,
                 i: ref Image): int;
    rgb2cmap:    fn(d: self ref Display, red, green, blue: int):
                 int;
    cmap2rgb:    fn(d: self ref Display, color: int):
                 (int, int, int);
    cursor:      fn(d: self ref Display, i: ref Image, p: ref Point):
                 int;
    cursorset:   fn(d: self ref Display, p : Point); };

DESCRIPTION

The Display type represents a connection to a draw(3) device. This device is the external representation of a physical display, such as a CRT, and its associated memory. It contains the storage for all images, even invisible ones, so all Image objects must be allocated through Display member functions.  Graphics operations that use multiple Image objects may not mix images from different Displays. 

image The visible contents of the display; draw on image to change the display. 

ones, zeros
Replicated images of a single pixel, either all ones (true, black) or all zeros (false, white). Useful as masks for basic graphical operations.

allocate(dev)
Attach to a new display, represented by the draw(3) device mounted in the specified dev directory.  If dev is the empty string, /dev is used.  The return value is nil if the allocation fails. 

d.startrefresh()
After allocating a Display object, the application should spawn a process to call startrefresh; this thread will receive and process window refresh events from the device. 

d.publicscreen(id)
Create a locally addressable pointer to a public Screen; see display-screen(2). 

d.newimage(r, ldepth, repl, color)
Allocate an off-screen Image.  The arguments supply values for the Image’s r, ldepth, and repl, and an initial color map index, used to paint the image when created.  The image’s clipr is initialized to r. 

d.color(color)
Creates a single-pixel, replicated off-screen image of the specified colour. The Draw module defines constants for several common colours: Draw−>Black, Draw−>Blue, Draw−>Green, Draw−>Red, Draw−>White, and Draw−>Yellow. 

d.rgb(red, green, blue)
Uses the values (from 0 (off) through 255 (full on)) of red, green, and blue to find the closest matching colour map entry, and create a single-pixel replicated image of that colour. Equivalent to d.color(d.rgb2cmap( r, g, b)). 

d.open(name)
Read an image description from the named file and return an Image holding the picture.  See image(6) for more information about image files.

d.readimage(fd)
Analogous to open, but from an open file descriptor rather than a named file. 

d.writeimage(fd, i)
Complement of readimage: write an image file representing i to the open file descriptor. 

d.rgb2cmap(red, green, blue)
Return the colour map index of the colour that best matches the colour triple.  The values of the components range from 0 (no colour) to 255 (saturated).

d.cmap2rgb(color)
Decompose the colour into a colour triple and return the result.

d.cursor(i, p)
Set the current cursor. If i is the image of the current display, then the graphics cursor will be set to its default value, otherwise i must be an image with ldepth 0 and the following rules apply: the size of the cursor will be half the horizontal height of i (subject to system-dependent restrictions on cursor size). The top half and the bottom half of the image are treated as two independent masks. When the cursor is drawn, pixels congruent with non-zero bits in the top half are cleared and then pixels congruent with non-zero bits in the bottom half are set.  P gives the offset added to the mouse position when drawing the cursor image. 

d.cursorset(p)
Set the position of the mouse cursor to p.

BUGS

The interface to cursor does not allow the use of colour mouse cursors, even on systems that allow them. The interface is likely to change in this respect.