OK, line spins inside a box until ctrl-c in the controlling terminal.
I wanted to get a sense of how fast or how much CPU it was going to
take, this takes under 4% CPU on a Raspberry Pi 3B. I only got my
first xlib program working a couple days ago.
My makefile has paths for both a Pi with Raspbian and OpenBSD I think:
spi: spi.c
gcc -O -Wall -g -o spi -I/usr/X11R6/include/ -I/usr/include \
-L/usr/X11R6/lib/ -lX11 spi.c
/*
My first recreational X activity. Based on Tronche's tutorial.
*/
#include <X11/Xlib.h> // Every Xlib program must include this
#include <assert.h> // I include this to test return values the lazy way
#include <unistd.h> // So we got the profile for 10 seconds
#include <stdio.h>
#include <stdlib.h> // for exit
#include <stdint.h> // for int16_t
#include <time.h> // for nanosleep
#define WWIDTH 320
#define WHEIGHT 240
Display *dpy;
int blackcolor,whitecolor;
Window w;
GC gc;
XEvent e; // a struct
uint16_t npoints;
uint16_t ends[WWIDTH+WHEIGHT][4]; // endpoints of lines
useconds_t us = 1000; // how long to leave a line on screen
void doloop(void) { // ctrl-c in terminal to stop
int i = 0;
while(1) {
XDrawLine(dpy,w,gc,ends[i][0],ends[i][1],ends[i][2],ends[i][3]);
XFlush(dpy);
usleep(us);
XDrawLine(dpy,w,gc,ends[i][0],ends[i][1],ends[i][2],ends[i][3]);
XFlush(dpy);
i++;
if (i > npoints)
i = 0;
}
}
/*
Filling ends[][] with endpoints of lines. Start with a horizontal line,
turn it 1 pixel CW, save the endpoints, going just inside WWIDTH. At the
top work across staying 1 pixel inside WHEIGHT. At the right side work
down to the midpoint. The line effectively flips over. I expected it to
rotate CW, not CCW. Oh well.
*/
void fillarray(void) { // define endpoints of lines
uint16_t yh = WHEIGHT/2;
uint16_t x,y;
int i,j;
y = yh;
for (i=0; i<yh; i++) { // up the left side
ends[i][0] = 1; // x
ends[i][1] = yh+i; // y
ends[i][2] = WWIDTH - 1; // inside right side
ends[i][3] = yh-i; // progresssing down lower right side
}
j = i+1; // position in array
for (x=1; x<WWIDTH; x++) { // across the top
ends[j][0] = x;
ends[j][1] = WHEIGHT -1;
ends[j][2] = WWIDTH - x; // working right-left in lr corner
ends[j][3] = 1;
j++;
}
for (y=0; y<yh; y++) { // down the right
ends[j][0] = WWIDTH-1;
ends[j][1] = WHEIGHT-y;
ends[j][2] = 1;
ends[j][3] = y;
j++;
}
npoints = j-1;
}
int main(void) {
fillarray();
dpy = XOpenDisplay(NULL);
assert(dpy); // be sure we've got dpy
blackcolor = BlackPixel(dpy, DefaultScreen(dpy));
whitecolor = WhitePixel(dpy, DefaultScreen(dpy));
w = XCreateSimpleWindow(dpy,DefaultRootWindow(dpy),0,0,WWIDTH,WHEIGHT,0,\
blackcolor,whitecolor); XSelectInput(dpy,w,StructureNotifyMask); //
XMapWindow(dpy,w); gc = XCreateGC(dpy,w,0,NULL);
XSetFunction(dpy,gc,GXxor); // sets xor mode
XSetForeground(dpy,gc,whitecolor);
// MapNotify wait loop, wait for a MapNotify event before drawing
// confirms that XMapWindow worked.
for (;;) {
XNextEvent(dpy,&e); // fetch an event
if (e.type == MapNotify) // done when we find one
break;
}
doloop();
return 0;
}
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