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#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <png.h>
#include <stdio.h>
#include <stdlib.h>
static unsigned char component(unsigned long pixel, unsigned long mask) {
if (!mask) return 0;
unsigned long shift = __builtin_ctzl(mask);
unsigned long bits = mask >> shift;
return (unsigned char)(((pixel & mask) >> shift) * 255 / bits);
}
int main(int argc, char **argv) {
if (argc != 2) return 2;
Display *d = XOpenDisplay(NULL);
if (!d) return 2;
int screen = DefaultScreen(d), width = DisplayWidth(d, screen), height = DisplayHeight(d, screen);
XImage *image = XGetImage(d, RootWindow(d, screen), 0, 0, width, height, AllPlanes, ZPixmap);
FILE *file = fopen(argv[1], "wb");
if (!image || !file) return 2;
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
png_infop info = png_create_info_struct(png);
if (setjmp(png_jmpbuf(png))) return 2;
png_init_io(png, file);
png_set_IHDR(png, info, width, height, 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
png_write_info(png, info);
unsigned char *row = malloc((size_t)width * 3);
if (!row) return 2;
for (int y = 0; y < height; ++y) {
for (int x = 0; x < width; ++x) {
unsigned long pixel = XGetPixel(image, x, y);
row[x * 3] = component(pixel, image->red_mask);
row[x * 3 + 1] = component(pixel, image->green_mask);
row[x * 3 + 2] = component(pixel, image->blue_mask);
}
png_write_row(png, row);
}
png_write_end(png, info);
free(row); png_destroy_write_struct(&png, &info);
XDestroyImage(image); fclose(file); XCloseDisplay(d);
return 0;
}
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