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#include <stdlib.h>
#include <stdio.h>
#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/keysym.h>
#include <X11/Xutil.h>
#define MIN(x, y) (x < y ? x : y)
#define MAX(x, y) (x > y ? x : y)
struct pointer_t {
int ret;
Bool sel;
int x0;
int y0;
int x1;
int y1;
};
void compimg(void);
void die(const char* s);
void quit(Bool ex);
void run(void);
void setup(void);
Display* dpy = NULL;
Window root = None;
int scr = -1;
struct pointer_t p = {0};
XImage* img = NULL;
void compimg(void)
{
/* create selection rectangle */
int rx = MIN(p.x0, p.x1);
int ry = MIN(p.y0, p.y1);
int rw = MAX(p.x0, p.x1) - rx;
int rh = MAX(p.y0, p.y1) - ry;
img = XGetImage(dpy, root, rx, ry, rw, rh, AllPlanes, ZPixmap);
if (!img)
die("XGetImage failed");
unsigned long p0 = XGetPixel(img, 0, 0);
fprintf(stderr, "first pixe =#%lx depth=%d bpp=%d\n", p0, img->depth, img->bits_per_pixel);
XDestroyImage(img);
quit(True);
}
void die(const char* s)
{
fprintf(stderr, "xnap: %s", s);
exit(EXIT_FAILURE);
}
void quit(Bool ex)
{
XUngrabPointer(dpy, CurrentTime);
XCloseDisplay(dpy);
if (ex)
exit(EXIT_SUCCESS);
}
void run(void)
{
XEvent ev;
for (;;) {
XNextEvent(dpy, &ev);
if (ev.type == KeyPress) {
KeySym ks = XLookupKeysym(&ev.xkey, 0);
if (ks == XK_Escape || ks == XK_q)
quit(True);
}
unsigned int b = ev.xbutton.button;
if (ev.type == ButtonPress && b == Button1) { /* start selecting */
p.sel = True;
p.x0 = p.x1 = ev.xbutton.x_root;
p.y0 = p.y1 = ev.xbutton.y_root;
}
else if (ev.type == MotionNotify && p.sel) { /* dragging selection */
p.x1 = ev.xmotion.x_root;
p.y1 = ev.xmotion.y_root;
}
else if (ev.type == ButtonRelease && p.sel && b == Button1) { /* release selection */
p.sel = False;
compimg();
}
}
}
void setup(void)
{
/* X surface */
dpy = XOpenDisplay(NULL);
if (dpy == NULL)
die ("failed to open display");
scr = DefaultScreen(dpy);
root = RootWindow(dpy, scr);
/* pointer */
p.ret = XGrabPointer(
dpy, root, False,
ButtonPressMask | ButtonReleaseMask | PointerMotionMask,
GrabModeAsync, GrabModeAsync, None, None, CurrentTime
);
if (p.ret != GrabSuccess)
die("XGrabPointer failed");
}
int main(int argc, char** argv)
{
(void) argc;
(void) argv;
setup();
run();
quit(True); /* unreachable */
return EXIT_SUCCESS;
}
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