I am on Ubuntu 14.04 platform, I am trying to make a rubberband for my screencasting project. I found rubberbanding examples which used xlib but I got flickering and partially missing rectangle while dragging mouse. I wonder if it's specific to my system or xlib library deprecated? Is there a workaround to fix it?
I also noticed that imagemagic's screen location grabbing command import window.miff flickers the same way.
Here are the codes that I tried
It just looks like the terminal in the background is repainting itself. You could always be selfish, and do an XGrabServer(), which WMs that use rectangles when moving/resizing windows do. Nothing else on the screen (clocks, load monitors) will update until you release the grab.
Server grabs should be avoided. You may want to add a --grab/--nograb option to let the user decide whether they prefer avoiding visual artifacts or let other applications (movie players, load monitors, clocks, ...) update the screen during the rubberbanding.
Another option would be to use a translucent window instead of an outlined rectangle, similar to how modern window managers tend to move/resize windows using real windows instead of rubberbands (even when that probably means repainting the window a lot of times before the operation is finished, for remote X move/resize with rubberbands is definitely better behaved).
Examples of XGrabServer() being obnoxious:
XGrabServer() while resizing windows freezing video playing on other windows, and playing havoc with streaming network connections.XGrabServer().
If you use xor in your GC you can selectively erase lines by drawing exactly the same thing again. You don't need to repaint the whole window.
XSetFunction(dpy,gc,GXxor); // sets xor mode
Just set up some buffers and keep a copy of what you draw so you can do it again (including the color).
I wrote this last year: https://www.raspberrypi.org/forums/viewtopic.php?p=1317849 I store the last 50 lines in a circular buffer then redraw them to erase. I can run it for hours with no incomplete erasure artifacts. And very low CPU usage. It's almost xscreensaver quality.
Definition: Rubberbanding is a screen selection rectangle drawn on the screen while dragging the mouse on the screen. When the mouse button releases, it prints geometry of the screen. X Window system lacks transparency in desktop, so it uses pseudo transparency by merging layers. The screen which includes desktop wallpaper is called "root window". To draw on the root window is a matter, because the other windows , for example a clock, need to repaint itself, in this case your rubberbanding rectangle flickers. To avoid this issue you need to use a translucent or transparent window which covers the whole screen.
Solution: As @ninjalj outlined in his answer you need to use transparent/translucent window which covers the whole screen.
Source Code:
// gcc xrubberband.c -o xrubberband -lX11
// use case ; maim -w root -g $(./xrubberband) `date +%H-%M-%S`.png
#include <stdio.h>
#include <X11/Xutil.h>
#include <X11/cursorfont.h>
#include <X11/extensions/XTest.h>
#include <X11/extensions/XInput.h>
#include <X11/Xos.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <stdlib.h>
#include <stdarg.h>
#include <X11/Xatom.h>
#define MAKE_RECT(etype) \
x = event.etype.x_root; \
y = event.etype.y_root; \
rw = x - rootx; \
if (rw < 0) rw = -rw; \
rh = y - rooty; \
if (rh < 0) rh = -rh; \
rx = x < rootx ? x : rootx; \
ry = y < rooty ? y : rooty
/* MAKE_CURSOR assigns a correct cursor */
#define MAKE_CURSOR(etype) \
pointer = (event.etype.x_root > rootx ? \
(event.etype.y_root > rooty ? pointer2 : pointer4) : \
(event.etype.y_root > rooty ? pointer3 : pointer1));
XRectangle Select_Rect(Display *dpy, int screen_num, Window root, Window parent, unsigned int display_width, unsigned int display_height)
{
int status;
XRectangle xrect;
XEvent event;
unsigned int x = 0, y = 0, rootx = 0, rooty = 0;
Cursor pointer1, pointer2, pointer3, pointer4, pointer;
int boxDrawn = False, selectionDone = False;
int rx = 0, ry = 0, rw = 0, rh = 0;
GC gc;
/* get some cursors for rectangle formation */
pointer1 = XCreateFontCursor(dpy, XC_ul_angle);
pointer2 = XCreateFontCursor(dpy, XC_lr_angle);
pointer3 = XCreateFontCursor(dpy, XC_ll_angle);
pointer4 = XCreateFontCursor(dpy, XC_ur_angle);
/* grab the pointer */
status = XGrabPointer(dpy, root, False, ButtonPressMask,
GrabModeAsync, GrabModeAsync, root,
pointer1, CurrentTime);
// if (status != GrabSuccess) Fatal_Error("Can't grab the mouse.");
//if (status != GrabSuccess) fprintf( stderr, "Can't grab the mouse.\n");
/* create a graphics context to draw with */
gc = XCreateGC(dpy, parent, 0, NULL);
// if (!gc) Fatal_Error("Could not get drawing resources.");
if (!gc) fprintf( stderr, "Could not get drawing resources.\n");
XSetSubwindowMode(dpy, gc, IncludeInferiors);
XSetForeground(dpy, gc, 255);
XSetFunction(dpy, gc, GXinvert);
/* get a button-press and pull out the root location */
XMaskEvent(dpy, ButtonPressMask, &event);
rootx = rx = event.xbutton.x_root;
rooty = ry = event.xbutton.y_root;
/* get pointer motion events */
XChangeActivePointerGrab(dpy, ButtonMotionMask | ButtonReleaseMask, pointer2, CurrentTime);
/* loop to let the user drag a rectangle */
while (!selectionDone) {
XNextEvent(dpy, &event);
switch(event.type) {
case ButtonRelease:
if (boxDrawn) {
XDrawRectangle(dpy, parent, gc, rx, ry, rw, rh);
boxDrawn = False;
}
XFlush(dpy);
/* record the final location */
MAKE_RECT(xbutton);
selectionDone = True;
break;
case MotionNotify:
if (boxDrawn) {
XDrawRectangle(dpy, parent, gc, rx, ry, rw, rh);
boxDrawn = False;
}
// while (XCheckTypedEvent(dpy, MotionNotify, &event)) { }
MAKE_RECT(xmotion);
XDrawRectangle(dpy, parent, gc, rx, ry, rw, rh);
boxDrawn = True;
MAKE_CURSOR(xmotion);
XChangeActivePointerGrab(dpy,
ButtonMotionMask | ButtonReleaseMask,
pointer, CurrentTime);
break;
}
}
xrect.x = rx;
xrect.y = ry;
xrect.width = rw;
xrect.height = rh;
/* release resources */
XFreeGC(dpy, gc);
XFreeCursor(dpy, pointer1);
XFreeCursor(dpy, pointer2);
XFreeCursor(dpy, pointer3);
XFreeCursor(dpy, pointer4);
XUngrabPointer(dpy, CurrentTime);
int x1 = rx + rw, y1 = ry + rh;
if ( display_width < x1 ) x1 = rx - rw;
if ( display_height < y1 ) y1 = ry - rh;
printf("\n%dx%d+%d+%d", rw, rh, rx, ry);
return xrect;
}
int main(int argc, char* argv[])
{
Display* dpy; /* pointer to X Display structure. */
int screen_num; /* number of screen to place the window on. */
Window win; /* pointer to the newly created window. */
unsigned int display_width,
display_height; /* height and width of the X display. */
unsigned int width, height; /* height and width for the new window. */
unsigned int win_x, win_y; /* location of the window's top-left corner. */
unsigned int win_border_width; /* width of window's border. */
char *display_name = getenv("DISPLAY"); /* address of the X display. */
Atom skip, state;
dpy = XOpenDisplay(display_name);
if (dpy == NULL) {
fprintf(stderr, "%s: cannot connect to X server '%s'\n",
argv[0], display_name);
exit(1);
}
/* get the geometry of the default screen for our display. */
screen_num = DefaultScreen(dpy);
display_width = DisplayWidth(dpy, screen_num);
display_height = DisplayHeight(dpy, screen_num);
// display_width =1280;
// display_height =800;
char *window_name = (char*)"Drawing window";
int whiteColor = WhitePixel(dpy, screen_num);
Window root = RootWindow(dpy,screen_num);
XVisualInfo vinfo;
XMatchVisualInfo(dpy, DefaultScreen(dpy), 32, TrueColor, &vinfo);
XSetWindowAttributes attr;
attr.colormap = XCreateColormap(dpy, root, vinfo.visual, AllocNone);
attr.border_pixel = 0;
attr.background_pixel = 0;
attr.override_redirect = 1;
attr.border_pixel = 0;
Window parent = XCreateWindow(dpy, root, 0, 0, display_width, display_height, 0, vinfo.depth, InputOutput, vinfo.visual, CWColormap | CWBorderPixel | CWBackPixel, &attr);
state = XInternAtom(dpy, "_NET_WM_STATE", True);
skip = XInternAtom(dpy, "_NET_WM_STATE_SKIP_TASKBAR", True);
Atom wm_delete_window = XInternAtom(dpy, "WM_DELETE_WINDOW", 0);
XSetWMProtocols(dpy, parent, &wm_delete_window, 1);
XChangeProperty(dpy, parent, state, XA_ATOM, 32,
PropModeReplace, (unsigned char*)&skip, 1);
XStoreName(dpy, parent, window_name);
XMapWindow(dpy, parent);
XSelectInput(dpy, parent, StructureNotifyMask| ButtonPressMask| PointerMotionMask| LeaveWindowMask| EnterWindowMask| ButtonReleaseMask );
Drawable d = parent;
XGCValues values;
values.line_width = 4;
values.line_style = LineSolid;
GC gc = XCreateGC(dpy, d, GCLineWidth, &values);
Select_Rect(dpy, screen_num, root, parent, display_width, display_height);
return 0;
}
I used #define MAKE_RECT(etype) from http://web.mit.edu/graphics/src/xgrabsc/xgrabsc.c