xrandr源码分析

1、XOpenDisplay 打开xrandr句柄，参数是显示后端xorg或者xwayland，也就是localhost:0.0

cpp 复制代码

dpy = XOpenDisplay (display_name); //XOpenDisplay(":0");

if (dpy == NULL) {
    fprintf (stderr, "Can't open display %s\n", XDisplayName(display_name));
    exit (1);
}

2、RootWindow通过screen下标获取到显示器设备句柄

cpp 复制代码

static int    screen = -1;
if (screen < 0)
    screen = DefaultScreen (dpy);

if (screen >= ScreenCount (dpy)) {
    fprintf (stderr, "Invalid screen number %d (display has %d)\n", screen, ScreenCount (dpy));
    exit (1);
}

root = RootWindow (dpy, screen);

3、获取屏幕信息XRRScreenResources（同时获取XRRGetScreenSizeRange最大，最小分辨率，XRRGetScreenResourcesCurrent/XRRGetScreenResources当前分辨率）

cpp 复制代码

static void
get_screen (Bool current)
{
    if (!has_1_2)
        fatal ("Server RandR version before 1.2\n");

    //已经获取到了，直接返回static XRRScreenResources  *res;
    if (res) 
        return;

    XRRGetScreenSizeRange (dpy, root, &minWidth, &minHeight, &maxWidth, &maxHeight);
    if (current)
        res = XRRGetScreenResourcesCurrent (dpy, root);
    else
        res = XRRGetScreenResources (dpy, root);
    if (!res) 
        fatal ("could not get screen resources");
}

4、获取crtcs

cpp 复制代码

typedef struct _XRRPanning {
    Time            timestamp;
    unsigned int left;
    unsigned int top;
    unsigned int width;
    unsigned int height;
    unsigned int track_left;
    unsigned int track_top;
    unsigned int track_width;
    unsigned int track_height;
    int          border_left;
    int          border_top;
    int          border_right;
    int          border_bottom;
} XRRPanning;

typedef struct _XRRModeInfo {
    RRMode        id;
    unsigned int    width;
    unsigned int    height;
    unsigned long    dotClock;
    unsigned int    hSyncStart;
    unsigned int    hSyncEnd;
    unsigned int    hTotal;
    unsigned int    hSkew;
    unsigned int    vSyncStart;
    unsigned int    vSyncEnd;
    unsigned int    vTotal;
    char        *name;
    unsigned int    nameLength;
    XRRModeFlags    modeFlags;
} XRRModeInfo;

typedef struct _XRRCrtcInfo {
    Time        timestamp;
    int            x, y;
    unsigned int    width, height;
    RRMode        mode;
    Rotation        rotation;
    int            noutput;
    RROutput        *outputs;
    Rotation        rotations;
    int            npossible;
    RROutput        *possible;
} XRRCrtcInfo;

struct _crtc {
    name_t        crtc;
    Bool        changing;
    XRRCrtcInfo        *crtc_info;
    XRRModeInfo        *mode_info;
    XRRPanning      *panning_info;
    int            x;
    int            y;
    Rotation        rotation;
    output_t        **outputs;
    int            noutput;
    transform_t        current_transform, pending_transform;
};

typedef struct _crtc crtc_t;

static void
get_crtcs (void)
{
    num_crtcs = res->ncrtc;
    crtcs = calloc (num_crtcs, sizeof (crtc_t)); //保存到crtcs
    if (!crtcs) 
        fatal ("out of memory\n");
    
    for (int c = 0; c < res->ncrtc; c++)
    {
        XRRCrtcInfo *crtc_info = XRRGetCrtcInfo (dpy, res, res->crtcs[c]);
        XRRCrtcTransformAttributes  *attr;
        XRRPanning  *panning_info = NULL;
        if (has_1_3) {
            XRRPanning zero;
            memset(&zero, 0, sizeof(zero));
            panning_info = XRRGetPanning  (dpy, res, res->crtcs[c]);
            zero.timestamp = panning_info->timestamp;
            if (!memcmp(panning_info, &zero, sizeof(zero))) {
                Xfree(panning_info);
                panning_info = NULL;
            }
        }

        set_name_xid (&crtcs[c].crtc, res->crtcs[c]);
        set_name_index (&crtcs[c].crtc, c);
        if (!crtc_info)
            fatal ("could not get crtc 0x%lx information\n", res->crtcs[c]);

        crtcs[c].crtc_info = crtc_info;
        crtcs[c].panning_info = panning_info;
        if (crtc_info->mode == None)
        {
            crtcs[c].mode_info = NULL;
            crtcs[c].x = 0;
            crtcs[c].y = 0;
            crtcs[c].rotation = RR_Rotate_0;
        }

        if (XRRGetCrtcTransform (dpy, res->crtcs[c], &attr) && attr) {
            set_transform (&crtcs[c].current_transform, &attr->currentTransform, attr->currentFilter, attr->currentParams, attr->currentNparams);
            XFree (attr);
        }else{
            init_transform (&crtcs[c].current_transform);
        }
        copy_transform (&crtcs[c].pending_transform, &crtcs[c].current_transform);
    }
}