BITBLT(2) BITBLT(2)
NAME
bitblt, bitbltclip, clipline, point, segment, polysegment,
arc, circle, disc, ellipse, texture, border, string,
strsize, strwidth, Fcode - graphics functions
SYNOPSIS
#include <u.h>
#include <libg.h>
void bitblt(Bitmap *db, Point dp, Bitmap *sb,
Rectangle sr, Fcode f)
int bitbltclip(void *)
int clipline(Rectangle r, Point *p0, Point *p1)
void point(Bitmap *b, Point p, int v, Fcode f)
void segment(Bitmap *b, Point p, Point q, int v, Fcode f)
void polysegment(Bitmap *b, int n, Point *pp, int v, Fcode f)
void circle(Bitmap *b, Point p, int r, int v, Fcode f)
void disc(Bitmap *b, Point p, int r, int v, Fcode)
void arc(Bitmap *b, Point p0, Point p1, Point p2, int v, Fcode f)
void ellipse(Bitmap *b, Point p, int a, int b, int v, Fcode f)
void texture(Bitmap *b, Rectangle r, Bitmap *t, Fcode f)
void border(Bitmap *b, Rectangle r, int w, Fcode f)
Point string(Bitmap *b, Point p, Font *ft, char *s, Fcode f)
Point strsize(Font *ft, char *s)
long strwidth(Font *ft, char *s)
enum Fcode {
Zero, DnorS, DandnotS, notS,
notDandS, notD, DxorS, DnandS,
DandS, DxnorS, D, DornotS,
S, notDorS, DorS, F,
} Fcode;
DESCRIPTION
Bitblt (bit-block transfer) takes bits from rectangle sr in
the source Bitmap sb and overlays them on a congruent
Page 1 Plan 9 (printed 12/22/24)
BITBLT(2) BITBLT(2)
rectangle with the min corner at point dp in the destination
bitmap, db. The f parameter defines each destination pixel
as a function of the source and destination pixels. The
sixteen codes in Fcode give all possible boolean operations
on the source S and destination D. The code values may be
expressed as boolean operations on the values S and D. For
example, D|S computes the result as the logical or of the
destination pixel's old value and the overlaying source
pixel's value. If pixels are more than one bit deep, the
operations are still bitwise. The Zero and F codes result
in new pixel values that are all zeros or all ones, respec-
tively.
If the source and destination bitmaps have different depths,
the source rectangle is first converted to have the same
depth as the destination, as follows: conversion to a
smaller number of bits per pixel is accomplished by taking
the desired number of high order bits; conversion to a
larger number of bits per pixel is accomplished by putting
the small value into the high order bits, and replicating it
as many times as necessary to fill the lower order bits.
All of the drawing graphics functions clip the rectangle
against the source and destination bitmaps' clip rectangles,
so that only pixels within the destination bitmap are
changed and none are changed that would have come from areas
outside the source bitmap. Bitbltclip takes a pointer to
the first argument of a bitblt argument list and clips dp
and sr so the resulting bitblt is confined to the source and
destination bitmaps. It returns one if the x and y dimen-
sions of the resulting bitblt are positive; zero otherwise.
Point changes the value of the destination point p in bitmap
b according to function code f. The source is a pixel with
value v. The constant ~0 represents the maximum pixel value.
Segment, circle, disc, and ellipse all draw in bitmap b with
function code f and a source pixel with value v. Arc draws a
circular arc centered on p0, traveling clockwise from p1 to
p2 or a point on the circle near p2. Segment draws a line
segment in bitmap b from point p to q. The segment is half-
open: p is the first point of the segment and q is the first
point beyond the segment, so adjacent segments sharing end-
points abut. Polysegment draws the n-1 segments joining the
n points in the array pointed to by pp. Clipline clips the
line segment from *p0 to *p1 (p0 is closed, p1 is open) to
rectangle r, adjusting p0 and p1 so that the segment is
within the rectangle and *p1 is closed. It returns 0 if
none of the segment is in the rectangle, 1 otherwise.
Circle draws a circle with radius r and center at point p.
Disc is the same except that it fills the circle. Ellipse
Page 2 Plan 9 (printed 12/22/24)
BITBLT(2) BITBLT(2)
draws an ellipse with horizontal semi-axis a and vertical
semi-axis b.
Border draws, with function f in bitmap b, the rectangular
outline with lines of width w fitting just inside rectangle
r.
Texture draws, with function f in bitmap b, a texture using
the bitmap specified by t. The texture bitmap is aligned on
b's coordinate system so that (0,0) in both coordinate sys-
tems coincide, and then t is replicated to form a tiling of
b. The tiling is clipped to rectangle r in b, and then
transferred to b using the specified function.
String draws the text characters given by the null-
terminated UTF string s into bitmap b, using font ft. The
upper left corner of the first character (i.e., a point that
is ft->ascent above the baseline) is placed at point p, and
subsequent characters are placed on the same baseline, dis-
placed to the right by the previous character's width. The
individual characters are bitblt'ed into the destination,
using drawing function f. String returns the point after the
final character of s; this can be outside b if the string
was clipped.
If a character in the string would have zero width, either
explicitly or because no image is present for the character
in the font, string replaces it with the image of the char-
acter with value zero (traditionally a `Peter face'). If
that character has zero width, string will get a fatal
error.
The bounding box for text to be drawn with string in font ft
can be found with strsize; it returns the max point of the
bounding box, assuming a min point of (0,0). Strwidth
returns the x-component of the max point.
SOURCE
/sys/src/libg
SEE ALSO
graphics(2), utf(6), add(2)
DIAGNOSTICS
These routines call the graphics error function on fatal
errors.
Page 3 Plan 9 (printed 12/22/24)