term% cat index.txt DRAW(2) System Calls Manual DRAW(2)
NAME
Image, draw, gendraw, drawreplxy, drawrepl, replclipr, line, poly,
fillpoly, bezier, bezspline, fillbezier, fillbezspline, ellipse, fil‐
lellipse, arc, fillarc, icossin, icossin2, border, string, stringn,
runestring, runestringn, stringbg, stringnbg, runestringbg,
runestringnbg, _string, ARROW, drawsetdebug - graphics functions
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <draw.h>
typedef
struct Image
{
Display *display; /* display holding data */
int id; /* id of system-held Image */
Rectangle r; /* rectangle in data area, local coords */
Rectangle clipr; /* clipping region */
ulong chan; /* pixel channel format descriptor */
int depth; /* number of bits per pixel */
int repl; /* flag: data replicates to tile clipr */
Screen *screen; /* 0 if not a window */
Image *next; /* next in list of windows */
} Image;
typedef enum
{
/* Porter-Duff compositing operators */
Clear = 0,
SinD = 8,
DinS = 4,
SoutD = 2,
DoutS = 1,
S = SinD|SoutD,
SoverD = SinD|SoutD|DoutS,
SatopD = SinD|DoutS,
SxorD = SoutD|DoutS,
D = DinS|DoutS,
DoverS = DinS|DoutS|SoutD,
DatopS = DinS|SoutD,
DxorS = DoutS|SoutD, /* == SxorD */
Ncomp = 12,
} Drawop;
void draw(Image *dst, Rectangle r, Image *src,
Image *mask, Point p)
void drawop(Image *dst, Rectangle r, Image *src,
Image *mask, Point p, Drawop op)
void gendraw(Image *dst, Rectangle r, Image *src, Point sp,
Image *mask, Point mp)
void gendrawop(Image *dst, Rectangle r, Image *src, Point sp,
Image *mask, Point mp, Drawop op)
int drawreplxy(int min, int max, int x)
Point drawrepl(Rectangle r, Point p)
void replclipr(Image *i, int repl, Rectangle clipr)
void line(Image *dst, Point p0, Point p1, int end0, int end1,
int radius, Image *src, Point sp)
void lineop(Image *dst, Point p0, Point p1, int end0, int end1,
int radius, Image *src, Point sp, Drawop op)
void poly(Image *dst, Point *p, int np, int end0, int end1,
int radius, Image *src, Point sp)
void polyop(Image *dst, Point *p, int np, int end0, int end1,
int radius, Image *src, Point sp, Drawop op)
void fillpoly(Image *dst, Point *p, int np, int wind,
Image *src, Point sp)
void fillpolyop(Image *dst, Point *p, int np, int wind,
Image *src, Point sp, Drawop op)
int bezier(Image *dst, Point p0, Point p1, Point p2, Point p3,
int end0, int end1, int radius, Image *src, Point sp)
int bezierop(Image *dst, Point p0, Point p1, Point p2, Point p3,
int end0, int end1, int radius, Image *src, Point sp,
Drawop op)
int bezspline(Image *dst, Point *pt, int npt, int end0, int end1,
int radius, Image *src, Point sp)
int bezsplineop(Image *dst, Point *pt, int npt, int end0, int end1,
int radius, Image *src, Point sp, Drawop op)
int bezsplinepts(Point *pt, int npt, Point **pp)
int fillbezier(Image *dst, Point p0, Point p1, Point p2, Point p3,
int w, Image *src, Point sp)
int fillbezierop(Image *dst, Point p0, Point p1, Point p2, Point p3,
int w, Image *src, Point sp, Drawop op)
int fillbezspline(Image *dst, Point *pt, int npt, int w,
Image *src, Point sp)
int fillbezsplineop(Image *dst, Point *pt, int npt, int w,
Image *src, Point sp, Drawop op)
void ellipse(Image *dst, Point c, int a, int b, int thick,
Image *src, Point sp)
void ellipseop(Image *dst, Point c, int a, int b, int thick,
Image *src, Point sp, Drawop op)
void fillellipse(Image *dst, Point c, int a, int b,
Image *src, Point sp)
void fillellipseop(Image *dst, Point c, int a, int b,
Image *src, Point sp, Drawop op)
void arc(Image *dst, Point c, int a, int b, int thick,
Image *src, Point sp, int alpha, int phi)
void arcop(Image *dst, Point c, int a, int b, int thick,
Image *src, Point sp, int alpha, int phi, Drawop op)
void fillarc(Image *dst, Point c, int a, int b, Image *src,
Point sp, int alpha, int phi)
void fillarcop(Image *dst, Point c, int a, int b, Image *src,
Point sp, int alpha, int phi, Drawop op)
int icossin(int deg, int *cosp, int *sinp)
int icossin2(int x, int y, int *cosp, int *sinp)
void border(Image *dst, Rectangle r, int i, Image *color, Point sp)
void borderop(Image *dst, Rectangle r, int i, Image *color, Point sp,
Drawop op)
Point string(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s)
Point stringop(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, Drawop op)
Point stringn(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, int len)
Point stringnop(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, int len, Drawop op)
Point runestring(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r)
Point runestringop(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, Drawop op)
Point runestringn(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, int len)
Point runestringnop(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, int len, Drawop op)
Point stringbg(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, Image *bg, Point bgp)
Point stringbgop(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, Image *bg, Point bgp, Drawop op)
Point stringnbg(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, int len, Image *bg, Point bgp)
Point stringnbgop(Image *dst, Point p, Image *src, Point sp,
Font *f, char *s, int len, Image *bg, Point bgp, Drawop op)
Point runestringbg(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, Image *bg, Point bgp)
Point runestringbgop(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, Image *bg, Point bgp, Drawop op)
Point runestringnbg(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, int len, Image *bg, Point bgp)
Point runestringnbgop(Image *dst, Point p, Image *src, Point sp,
Font *f, Rune *r, int len, Image *bg, Point bgp, Drawop op)
Point _string(Image *dst, Point p, Image *src,
Point sp, Font *f, char *s, Rune *r, int len,
Rectangle clipr, Image *bg, Point bgp, Drawop op)
void drawsetdebug(int on)
enum
{
/* line ends */
Endsquare = 0,
Enddisc = 1,
Endarrow = 2,
Endmask = 0x1F
};
#define ARROW(a, b, c) (Endarrow|((a)<<5)|((b)<<14)|((c)<<23))
DESCRIPTION
The Image type defines rectangular pictures and the methods to draw
upon them; it is also the building block for higher level objects such
as windows and fonts. In particular, a window is represented as an Im‐
age; no special operators are needed to draw on a window.
r The coordinates of the rectangle in the plane for which the
Image has defined pixel values. It should not be modified
after the image is created.
clipr The clipping rectangle: operations that read or write the im‐
age will not access pixels outside clipr. Frequently, clipr
is the same as r, but it may differ; see in particular the
discussion of repl. The clipping region may be modified dy‐
namically using replclipr (q.v.).
chan The pixel channel format descriptor, as described in im‐
age(6). The value should not be modified after the image is
created.
depth The number of bits per pixel in the picture; it is identi‐
cally chantodepth(chan) (see graphics(2)) and is provided as
a convenience. The value should not be modified after the
image is created.
repl A boolean value specifying whether the image is tiled to
cover the plane when used as a source for a drawing opera‐
tion. If repl is zero, operations are restricted to the in‐
tersection of r and clipr. If repl is set, r defines the
tile to be replicated and clipr defines the portion of the
plane covered by the tiling, in other words, r is replicated
to cover clipr; in such cases r and clipr are independent.
For example, a replicated image with r set to
((0, 0), (1, 1)) and clipr set to ((0, 0), (100, 100)), with
the single pixel of r set to blue, behaves identically to an
image with r and clipr both set to ((0, 0), (100, 100)) and
all pixels set to blue. However, the first image requires
far less memory. The replication flag may be modified dynam‐
ically using replclipr (q.v.).
Most of the drawing functions come in two forms: a basic form, and an
extended form that takes an extra Drawop to specify a Porter-Duff com‐
positing operator to use. The basic forms assume the operator is
SoverD, which suffices for the vast majority of applications. The ex‐
tended forms are named by adding an -op suffix to the basic form. Only
the basic forms are listed below.
draw(dst, r, src, mask, p)
Draw is the standard drawing function. Only those pixels within
the intersection of dst->r and dst->clipr will be affected; draw
ignores dst->repl. The operation proceeds as follows (this is a
description of the behavior, not the implementation):
1. If repl is set in src or mask, replicate their contents
to fill their clip rectangles.
2. Translate src and mask so p is aligned with r.min.
3. Set r to the intersection of r and dst->r.
4. Intersect r with src->clipr. If src->repl is false, also
intersect r with src->r.
5. Intersect r with mask->clipr. If mask->repl is false,
also intersect r with mask->r.
6. For each location in r, combine the dst pixel with the
src pixel using the alpha value corresponding to the mask
pixel. If the mask has an explicit alpha channel, the
alpha value corresponding to the mask pixel is simply
that pixel's alpha channel. Otherwise, the alpha value
is the NTSC greyscale equivalent of the color value, with
white meaning opaque and black transparent. In terms of
the Porter-Duff compositing algebra, draw replaces the
dst pixels with (src in mask) over dst. (In the extended
form, ‘‘over'' is replaced by op).
The various pixel channel formats involved need not be identi‐
cal. If the channels involved are smaller than 8-bits, they
will be promoted before the calculation by replicating the ex‐
tant bits; after the calculation, they will be truncated to
their proper sizes.
gendraw(dst, r, src, p0, mask, p1)
Similar to draw except that gendraw aligns the source and mask
differently: src is aligned so p0 corresponds to r.min and mask
is aligned so p1 corresponds to r.min. For most purposes with
simple masks and source images, draw is sufficient, but gendraw
is the general operator and the one all other drawing primitives
are built upon.
drawreplxy(min,max,x)
Clips x to be in the half-open interval [min, max) by adding or
subtracting a multiple of max-min.
drawrepl(r,p)
Clips the point p to be within the rectangle r by translating
the point horizontally by an integer multiple of rectangle width
and vertically by the height.
replclipr(i,repl,clipr)
Because the image data is stored on the server, local modifica‐
tions to the Image data structure itself will have no effect.
Repclipr modifies the local Image data structure's repl and
clipr fields, and notifies the server of their modification.
line(dst, p0, p1, end0, end1, thick, src, sp)
Line draws in dst a line of width 1+2*thick pixels joining
points p0 and p1. The line is drawn using pixels from the src
image aligned so sp in the source corresponds to p0 in the des‐
tination. The line touches both p0 and p1, and end0 and end1
specify how the ends of the line are drawn. Endsquare termi‐
nates the line perpendicularly to the direction of the line; a
thick line with Endsquare on both ends will be a rectangle.
Enddisc terminates the line by drawing a disc of diameter
1+2*thick centered on the end point. Endarrow terminates the
line with an arrowhead whose tip touches the endpoint.
The macro ARROW permits explicit control of the shape of the ar‐
row. If all three parameters are zero, it produces the default
arrowhead, otherwise, a sets the distance along line from end of
the regular line to tip, b sets the distance along line from the
barb to the tip, and c sets the distance perpendicular to the
line from edge of line to the tip of the barb, all in pixels.
Line and the other geometrical operators are equivalent to calls
to gendraw using a mask produced by the geometric procedure.
poly(dst, p, np, end0, end1, thick, src, sp)
Poly draws a general polygon; it is conceptually equivalent to a
series of calls to line joining adjacent points in the array of
Points p, which has np elements. The ends of the polygon are
specified as in line; interior lines are terminated with Enddisc
to make smooth joins. The source is aligned so sp corresponds
to p[0].
fillpoly(dst, p, np, wind, src, sp)
Fillpoly is like poly but fills in the resulting polygon rather
than outlining it. The source is aligned so sp corresponds to
p[0]. The winding rule parameter wind resolves ambiguities
about what to fill if the polygon is self-intersecting. If wind
is ~0, a pixel is inside the polygon if the polygon's winding
number about the point is non-zero. If wind is 1, a pixel is
inside if the winding number is odd. Complementary values (0 or
~1) cause outside pixels to be filled. The meaning of other
values is undefined. The polygon is closed with a line if nec‐
essary.
bezier(dst, a, b, c, d, end0, end1, thick, src, sp)
Bezier draws the cubic Bezier curve defined by Points a, b, c,
and d. The end styles are determined by end0 and end1; the
thickness of the curve is 1+2*thick. The source is aligned so
sp in src corresponds to a in dst.
bezspline(dst, p, np, end0, end1, thick, src, sp)
Bezspline takes the same arguments as poly but draws a quadratic
B-spline (despite its name) rather than a polygon. If the first
and last points in p are equal, the spline has periodic end con‐
ditions.
bezsplinepts(pt, npt, pp)
Bezsplinepts returns in pp a list of points making up the open
polygon that bezspline would draw. The caller is responsible
for freeing *pp.
fillbezier(dst, a, b, c, d, wind, src, sp)
Fillbezier is to bezier as fillpoly is to poly.
fillbezspline(dst, p, wind, src, sp)
Fillbezspline is like fillpoly but fills the quadratic B-spline
rather than the polygon outlined by p. The spline is closed
with a line if necessary.
ellipse(dst, c, a, b, thick, src, sp)
Ellipse draws in dst an ellipse centered on c with horizontal
and vertical semiaxes a and b. The source is aligned so sp in
src corresponds to c in dst. The ellipse is drawn with thick‐
ness 1+2*thick.
fillellipse(dst, c, a, b, src, sp)
Fillellipse is like ellipse but fills the ellipse rather than
outlining it.
arc(dst, c, a, b, thick, src, sp, alpha, phi)
Arc is like ellipse, but draws only that portion of the ellipse
starting at angle alpha and extending through an angle of phi.
The angles are measured in degrees counterclockwise from the
positive x axis.
fillarc(dst, c, a, b, src, sp, alpha, phi)
Fillarc is like arc, but fills the sector with the source color.
icossin(deg, cosp, sinp)
Icossin stores in *cosp and *sinp scaled integers representing
the cosine and sine of the angle deg, measured in integer de‐
grees. The values are scaled so cos(0) is 1024.
icossin2(x, y, cosp, sinp)
Icossin2 is analogous to icossin, with the angle represented not
in degrees but implicitly by the point (x,y). It is to icossin
what atan2 is to atan (see sin(2)).
border(dst, r, i, color, sp)
Border draws an outline of rectangle r in the specified color.
The outline has width i; if positive, the border goes inside the
rectangle; negative, outside. The source is aligned so sp cor‐
responds to r.min.
string(dst, p, src, sp, font, s)
String draws in dst characters specified by the string s and
font; it is equivalent to a series of calls to gendraw using
source src and masks determined by the character shapes. The
text is positioned with the left of the first character at p.x
and the top of the line of text at p.y. The source is posi‐
tioned so sp in src corresponds to p in dst. String returns a
Point that is the position of the next character that would be
drawn if the string were longer.
For characters with undefined or zero-width images in the font,
the character at font position 0 (NUL) is drawn.
The other string routines are variants of this basic form, and
have names that encode their variant behavior. Routines whose
names contain rune accept a string of Runes rather than UTF-en‐
coded bytes. Routines ending in n accept an argument, n, that
defines the number of characters to draw rather than accepting a
NUL-terminated string. Routines containing bg draw the back‐
ground behind the characters in the specified color (bg) and
alignment (bgp); normally the text is drawn leaving the back‐
ground intact.
The routine _string captures all this behavior into a single op‐
erator. Whether it draws a UTF string or Rune string depends on
whether s or r is null (the string length is always determined
by len). If bg is non-null, it is used as a background color.
The clipr argument allows further management of clipping when
drawing the string; it is intersected with the usual clipping
rectangles to further limit the extent of the text.
drawsetdebug(on)
Turns on or off debugging output (usually to a serial line) ac‐
cording to whether on is non-zero.
SOURCE
/sys/src/libdraw
SEE ALSO
graphics(2), stringsize(2), color(6), utf(6), addpt(2)
T. Porter, T. Duff. ‘‘Compositing Digital Images'', Computer Graphics
(Proc. SIGGRAPH), 18:3, pp. 253-259, 1984.
DIAGNOSTICS
These routines call the graphics error function on fatal errors.
BUGS
Anti-aliased characters can be drawn by defining a font with multiple
bits per pixel, but there are no anti-aliasing geometric primitives.
DRAW(2)