X11: MIT-SHM (共有メモリイメージ)

$ cc -o run 20-shm util.c -lX11 -lXext

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/extensions/XShm.h>
#include "util.h"

#define WIDTH  200
#define HEIGHT 200

static void _draw_image(XImage *img)
{
    uint8_t *pd,*pdY;
    int ix,iy,bytes;
    uint32_t pixcol;

    pdY = (uint8_t *)img->data;
    bytes = img->bits_per_pixel / 8;

    for(iy = 0; iy < img->height; iy++)
    {
        pd = pdY;

        pixcol = rgb_to_pixel_sep(
            iy * 255 / (img->height - 1), 0, 0);
        
        for(ix = 0; ix < img->width; ix++)
        {
            ximage_setbuf(img, pd, pixcol);
            
            pd += bytes;
        }

        pdY += img->bytes_per_line;
    }
}

int main(int argc,char **argv)
{
    Display *disp;
    XSetWindowAttributes attr;
    Window win;
    XEvent ev;
    XImage *ximg = NULL;
    XShmSegmentInfo si;
    int completion_type;
    
    disp = XOpenDisplay(NULL);
    if(!disp) return 1;

    set_display(disp);

    //MIT-SHM

    if(!XShmQueryExtension(disp))
    {
        printf("unsupported MIT-SHM\n");
        XCloseDisplay(disp);
        return 1;
    }

    completion_type = XShmGetEventBase(disp) + ShmCompletion;

    //ウィンドウ作成

    attr.event_mask = ButtonPressMask | ExposureMask;

    win = XCreateWindow(disp, DefaultRootWindow(disp),
        0, 0, WIDTH, HEIGHT, 0,
        CopyFromParent, CopyFromParent, CopyFromParent,
        CWEventMask, &attr);

    //----- XImage

    //XImage 作成

    ximg = XShmCreateImage(disp, NULL, g_disp.depth,
        ZPixmap, NULL, &si, WIDTH, HEIGHT);

    if(!ximg)
    {
        printf("failed XCreateImage\n");
        goto END;
    }

    printf("depth: %d\nbits_per_pixel: %d\nbytes_per_line: %d\n",
        ximg->depth, ximg->bits_per_pixel, ximg->bytes_per_line);

    //共有メモリを作り、識別子を取得 (負の値で失敗)

    si.shmid = shmget(IPC_PRIVATE,
        ximg->bytes_per_line * ximg->height, IPC_CREAT | 0777);

    printf("shmid: %d\n", si.shmid);

    //共有メモリをプロセスのアドレス空間にアタッチ

    si.shmaddr = ximg->data = shmat(si.shmid, 0, 0);

    si.readOnly = False;

    //共有メモリセグメントを X サーバーにアタッチ

    XShmAttach(disp, &si);

    printf("shmseg: 0x%lx\n", si.shmseg);

    //

    _draw_image(ximg);

    //---- イベント

    XMapWindow(disp, win);

    while(1)
    {
        XNextEvent(disp, &ev);

        if(ev.type == completion_type)
        {
            printf("[ShmCompletion] shmseg:0x%lx\n",
                ((XShmCompletionEvent *)&ev)->shmseg);
            fflush(stdout);
            continue;
        }

        switch(ev.type)
        {
            case Expose:
                XShmPutImage(disp, win, g_disp.gc, ximg,
                    ev.xexpose.x, ev.xexpose.y,
                    ev.xexpose.x, ev.xexpose.y,
                    ev.xexpose.width, ev.xexpose.height, True);

                printf("[Expose] (%d,%d)-(%dx%d)\n",
                    ev.xexpose.x, ev.xexpose.y, ev.xexpose.width, ev.xexpose.height);
                fflush(stdout);
                break;
            case ButtonPress:
                goto END;
        }
    }

END:
    if(ximg)
    {
        XShmDetach(disp, &si);
        XDestroyImage(ximg);

        //共有メモリをプロセスのアドレス空間から切り離す
        shmdt(si.shmaddr);
        //共有メモリの解放
        shmctl(si.shmid, IPC_RMID, 0);
    }

    XCloseDisplay(disp);

    return 0;
}