I am attempting to create a thumbnailer (for i3wm on linux) which generates an icon from a screenshot for all the available windows. The aim being to replicate something like how windows uses Alt-Tab to produce a pane of windows to choose from;
The current prototype uses pygtk to generate the dialog, and it creates thumbnails of the windows in the _NET_CLIENT_LIST using XGetImage where the windows have been redirected using XCompositeRedirectWindow. It works pretty well except for that images captured from windows which are browsers, (e.g. firefox, chrome, electron) are mangled, or wrong;
Basically, tools like xwd, scrot and import don't work for the hidden windows in i3, presumably because they are unmapped. So I have pulled some code together to create the thumbnails. The core of it is based on an example using XCompositeRedirectWindow from X11/extensions/Xcomposite.h from here.
My attempt at creating a short example is here;
https://gist.github.com/tolland/4bb1e97db258b92618adfb783ce66fac
it can be compiled with;
$ gcc example.c -lX11 -lXcomposite -lXrender -lpng -o example
and then to output png files for each of the windows;
$ mkdir -p /tmp/png_out && ./example
will produce pngs for each of the images
window found was 58720312
found window name for 58720312 : build : sudo
filename /tmp/png_out/58720312_test3.png
window found was 79691781
found window name for 79691781 : .xsession-errors - glogg
filename /tmp/png_out/79691781_test3.png
window found was 62914576
found window name for 62914576 : Edit - Stack Overflow - Mozilla Firefox
filename /tmp/png_out/62914576_test3.png
So the code I am currently using to walk the _NET_CLIENT_LIST is this;
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <libpng16/png.h>
#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/extensions/Xcomposite.h>
#include <X11/extensions/Xrender.h>
//Compile hint: gcc -shared -O3 -lX11 -fPIC -Wl,-soname,prtscn -o prtscn.so prtscn.c
typedef int bool;
#define true 1
#define false 0
const int DEBUG = 0;
void getScreen2(const int, const int, const int, const int, const XID);
void write_png_for_image(XImage *image, XID xid, int width, int height,
char *filename);
typedef int (*handler)(Display *, XErrorEvent *);
XID getWindows(Display *display, Window parent, Window window, XID xid,
int depth);
int main() {
Display *display = XOpenDisplay(NULL);
Window root = DefaultRootWindow(display);
uint nwindows;
Window root_return, parent_return, *windows;
Atom a = XInternAtom(display, "_NET_CLIENT_LIST", true);
Atom actualType;
int format;
unsigned long numItems, bytesAfter;
unsigned char *data = 0;
int status = XGetWindowProperty(display, root, a, 0L, (~0L),
false,
AnyPropertyType, &actualType, &format, &numItems, &bytesAfter, &data);
char* window_name_return;
if (status >= Success && numItems) {
long *array = (long*) data;
for (long k = 0; k < numItems; k++) {
Window window = (Window) array[k];
//not finding chrome window name
printf("window found was %d \n", window);
if (XFetchName(display, window, &window_name_return)) {
printf("found window name for %d : %s \n", window,
window_name_return);
}
//XMapWindow(display, parent);
XMapWindow(display, window);
XWindowAttributes attr;
Status status = XGetWindowAttributes(display, window, &attr);
if (status == 0)
printf("Fail to get window attributes!\n");
getScreen2(0, 0, attr.width, attr.height, window);
}
XFree(data);
}
return 0;
}
which calls this function to map the window and call XCompositeRedirectWindow;
void getScreen2(const int xx, const int yy, const int W, const int H,
const XID xid) {
Display *display = XOpenDisplay(NULL);
Window root = DefaultRootWindow(display);
// turn on --sync to force error on correct method
//https://www.x.org/releases/X11R7.6/doc/man/man3/XSynchronize.3.xhtml
XSynchronize(display, True);
int counter = 1;
// select which xid to operate on, the winder or its parent
//XID xwid = fparent;
XID xwid = xid;
// Requests the X server to direct the hierarchy starting at window to off-screen storage
XCompositeRedirectWindow(display, xwid, CompositeRedirectAutomatic);
XWindowAttributes attr;
Status status = XGetWindowAttributes(display, xwid, &attr);
int width = attr.width;
int height = attr.height;
int depth = attr.depth;
Pixmap xc_pixmap = XCompositeNameWindowPixmap(display, xwid);
if (!xc_pixmap) {
printf("xc_pixmap not found\n");
}
//XWriteBitmapFile(display, "test1.xpm", pixmap, W, H, -1, -1);
XRenderPictFormat *format = XRenderFindVisualFormat(display, attr.visual);
XRenderPictureAttributes pa;
pa.subwindow_mode = IncludeInferiors;
Picture picture = XRenderCreatePicture(display, xwid, format,
CPSubwindowMode, &pa);
char buffer[50];
int n;
int file_counter = 1;
n = sprintf(buffer, "/tmp/%d_test%d.xpm", xid, file_counter++);
XWriteBitmapFile(display, buffer, xc_pixmap, W, H, -1, -1);
n = sprintf(buffer, "/tmp/%d_test%d.xpm", xid, file_counter++);
XWriteBitmapFile(display, buffer, xid, W, H, -1, -1);
XImage *image = XGetImage(display, xid, 0, 0, W, H, AllPlanes, ZPixmap);
if (!image) {
printf("XGetImage failed\n");
}
char filename[255];
int n2;
n2 = sprintf(filename, "/tmp/png_out/%d_test%d.png", xid, file_counter++);
printf("filename %s \n", filename);
write_png_for_image(image, xid, W, H, filename);
//XFree(image);
XDestroyImage(image);
XDestroyWindow(display, root);
XCloseDisplay(display);
}
and then this to write out the png;
void write_png_for_image(XImage *image, XID xid, int width, int height,
char *filename) {
int code = 0;
FILE *fp;
png_structp png_ptr;
png_infop png_info_ptr;
png_bytep png_row;
char buffer[50];
int n;
n = sprintf(buffer, filename, xid);
// Open file
fp = fopen(buffer, "wb");
if (fp == NULL) {
fprintf(stderr, "Could not open file for writing\n");
code = 1;
}
// Initialize write structure
png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (png_ptr == NULL) {
fprintf(stderr, "Could not allocate write struct\n");
code = 1;
}
// Initialize info structure
png_info_ptr = png_create_info_struct(png_ptr);
if (png_info_ptr == NULL) {
fprintf(stderr, "Could not allocate info struct\n");
code = 1;
}
// Setup Exception handling
if (setjmp(png_jmpbuf (png_ptr))) {
fprintf(stderr, "Error during png creation\n");
code = 1;
}
png_init_io(png_ptr, fp);
// Write header (8 bit colour depth)
png_set_IHDR(png_ptr, png_info_ptr, width, height, 8, PNG_COLOR_TYPE_RGB,
PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
// Set title
char *title = "Screenshot";
if (title != NULL) {
png_text title_text;
title_text.compression = PNG_TEXT_COMPRESSION_NONE;
title_text.key = "Title";
title_text.text = title;
png_set_text(png_ptr, png_info_ptr, &title_text, 1);
}
png_write_info(png_ptr, png_info_ptr);
// Allocate memory for one row (3 bytes per pixel - RGB)
png_row = (png_bytep) malloc(3 * width * sizeof(png_byte));
unsigned long red_mask = image->red_mask;
unsigned long green_mask = image->green_mask;
unsigned long blue_mask = image->blue_mask;
// Write image data
//int xxx, yyy;
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
unsigned long pixel = XGetPixel(image, x, y);
unsigned char blue = pixel & blue_mask;
unsigned char green = (pixel & green_mask) >> 8;
unsigned char red = (pixel & red_mask) >> 16;
png_byte *ptr = &(png_row[x * 3]);
ptr[0] = red;
ptr[1] = green;
ptr[2] = blue;
}
png_write_row(png_ptr, png_row);
}
// End write
png_write_end(png_ptr, NULL);
// Free
fclose(fp);
if (png_info_ptr != NULL)
png_free_data(png_ptr, png_info_ptr, PNG_FREE_ALL, -1);
if (png_ptr != NULL)
png_destroy_write_struct(&png_ptr, (png_infopp) NULL);
if (png_row != NULL)
free(png_row);
}
However when the windows is browser based, the image is mangled like so;
Do I need to do something special to get browser windows working?
References;
https://www.talisman.org/~erlkonig/misc/x11-composite-tutorial/
Get a screenshot of a window that is cover or not visible or minimized with Xcomposite extension for X11
