glenda.party
term% ls -F
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)
       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
       Image; 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
                 image  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
                 dynamically using replclipr (q.v.).

       chan      The  pixel  channel  format  descriptor,  as   described   in
                 image(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
                 intersection 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
       extended  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
              extant 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
              arrow.  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 perpen‐
              dicular 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, 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
              degrees.  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-
              encoded 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
              operator.   Whether it draws a UTF string or Rune string depends
              on whether s or r is null (the string length  is  always  deter‐
              mined  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 clip‐
              ping rectangles to further limit the extent of the text.

       drawsetdebug(on)
              Turns on or off debugging output  (usually  to  a  serial  line)
              according 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)