term% cat index.txt BITBLT(2) System Calls Manual 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 rectangle with the min cor‐
ner at point dp in the destination bitmap, db. The f parameter defines
each destination pixel as a function of the source and destination pix‐
els. 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, respectively.
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 accom‐
plished 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 destina‐
tion bitmaps. It returns one if the x and y dimensions of the result‐
ing bitblt are positive; zero otherwise.
Point changes the value of the destination point p in bitmap b accord‐
ing to function code f. The source is a pixel with value v. The con‐
stant ~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 cen‐
tered 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 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 systems coincide, and then t is repli‐
cated 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, displaced 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 character with value zero (tradition‐
ally 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, as‐
suming 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.
BITBLT(2)