public static class WindowManager.LayoutParams extends ViewGroup.LayoutParams
	    implements Parcelable {
	// x坐标
    public int x;
    // y坐标
    public int y;
    // 类型(WMS根据type确定Z-Order)
    public int type;
	...
}

// 计算主序时乘以10000, 目的是为同类型的多个窗口预留空间和Z-Order调整
static final int TYPE_LAYER_MULTIPLIER = 10000;
// 计算主序时加1000, 目的是确定相同主序的子窗口相对于父窗口的上下位置
static final int TYPE_LAYER_OFFSET = 1000;
  
// 表示主序
final int mBaseLayer;
// 表示子序
final int mSubLayer;
 
WindowState(WindowManagerService service, Session s, IWindow c, WindowToken token,
        WindowState attachedWindow, int appOp, int seq, WindowManager.LayoutParams a,
        int viewVisibility, final DisplayContent displayContent) {
    ...
    // 若当前窗口类型为子窗口
    if ((mAttrs.type >= FIRST_SUB_WINDOW && mAttrs.type <= LAST_SUB_WINDOW)) {
        // 计算主序, 主序与父窗口一致，主序大的窗口位于主序小的窗口上面
        mBaseLayer = mPolicy.getWindowLayerLw(parentWindow) * TYPE_LAYER_MULTIPLIER + TYPE_LAYER_OFFSET;
        // 计算子序
        mSubLayer = mPolicy.getSubWindowLayerFromTypeLw(a.type);
        ...
    } else { // 若当前窗口类型不是子窗口
        // 计算主序
        mBaseLayer = mPolicy.getWindowLayerLw(this) * TYPE_LAYER_MULTIPLIER + TYPE_LAYER_OFFSET;
        // 子序为0
        mSubLayer = 0;
        ...
    }
    ...
}

default int getWindowLayerLw(WindowState win) {
    return getWindowLayerFromTypeLw(win.getBaseType(), win.canAddInternalSystemWindow());
}

default int getWindowLayerFromTypeLw(int type) {
    if (isSystemAlertWindowType(type)) {
        throw new IllegalArgumentException("Use getWindowLayerFromTypeLw() or getWindowLayerLw() for alert window types");
    }
    return getWindowLayerFromTypeLw(type, false /* canAddInternalSystemWindow */);
}

default int getWindowLayerFromTypeLw(int type, boolean canAddInternalSystemWindow) {
    if (type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW) {
        return APPLICATION_LAYER; // 2
    }
 
    switch (type) {
        case TYPE_WALLPAPER:
            // wallpaper is at the bottom, though the window manager may move it.
            return  1;
        case TYPE_PRESENTATION:
        case TYPE_PRIVATE_PRESENTATION:
        case TYPE_DOCK_DIVIDER:
        case TYPE_QS_DIALOG:
            return  APPLICATION_LAYER;
        case TYPE_PHONE:
            return  3;
        case TYPE_SEARCH_BAR:
        case TYPE_VOICE_INTERACTION_STARTING:
            return  4;
        case TYPE_VOICE_INTERACTION:
            // voice interaction layer is almost immediately above apps.
            return  5;
        case TYPE_INPUT_CONSUMER:
            return  6;
        case TYPE_SYSTEM_DIALOG:
            return  7;
        case TYPE_TOAST:
            // toasts and the plugged-in battery thing
            return  8;
        case TYPE_PRIORITY_PHONE:
            // SIM errors and unlock.  Not sure if this really should be in a high layer.
            return  9;
        case TYPE_SYSTEM_ALERT:
            // like the ANR / app crashed dialogs
            // Type is deprecated for non-system apps. For system apps, this type should be
            // in a higher layer than TYPE_APPLICATION_OVERLAY.
            return  canAddInternalSystemWindow ? 13 : 10;
        case TYPE_APPLICATION_OVERLAY:
            return  12;
        case TYPE_DREAM:
            // used for Dreams (screensavers with TYPE_DREAM windows)
            return  14;
        case TYPE_INPUT_METHOD:
            // on-screen keyboards and other such input method user interfaces go here.
            return  15;
        case TYPE_INPUT_METHOD_DIALOG:
            // on-screen keyboards and other such input method user interfaces go here.
            return  16;
        case TYPE_STATUS_BAR:
            return  17;
        case TYPE_STATUS_BAR_PANEL:
            return  18;
        case TYPE_STATUS_BAR_SUB_PANEL:
            return  19;
        case TYPE_KEYGUARD_DIALOG:
            return  20;
        case TYPE_VOLUME_OVERLAY:
            // the on-screen volume indicator and controller shown when the user
            // changes the device volume
            return  21;
        case TYPE_SYSTEM_OVERLAY:
            // the on-screen volume indicator and controller shown when the user
            // changes the device volume
            return  canAddInternalSystemWindow ? 22 : 11;
        case TYPE_NAVIGATION_BAR:
            // the navigation bar, if available, shows atop most things
            return  23;
        case TYPE_NAVIGATION_BAR_PANEL:
            // some panels (e.g. search) need to show on top of the navigation bar
            return  24;
        case TYPE_SCREENSHOT:
            // screenshot selection layer shouldn't go above system error, but it should cover
            // navigation bars at the very least.
            return  25;
        case TYPE_SYSTEM_ERROR:
            // system-level error dialogs
            return  canAddInternalSystemWindow ? 26 : 10;
        case TYPE_MAGNIFICATION_OVERLAY:
            // used to highlight the magnified portion of a display
            return  27;
        case TYPE_DISPLAY_OVERLAY:
            // used to simulate secondary display devices
            return  28;
        case TYPE_DRAG:
            // the drag layer: input for drag-and-drop is associated with this window,
            // which sits above all other focusable windows
            return  29;
        case TYPE_ACCESSIBILITY_OVERLAY:
            // overlay put by accessibility services to intercept user interaction
            return  30;
        case TYPE_SECURE_SYSTEM_OVERLAY:
            return  31;
        case TYPE_BOOT_PROGRESS:
            return  32;
        case TYPE_POINTER:
            // the (mouse) pointer layer
            return  33;
        default:
            return APPLICATION_LAYER;
    }
}

default int getSubWindowLayerFromTypeLw(int type) {
    switch (type) {
        case TYPE_APPLICATION_PANEL:
        case TYPE_APPLICATION_ATTACHED_DIALOG:
            return APPLICATION_PANEL_SUBLAYER; // 1
        case TYPE_APPLICATION_MEDIA:
            return APPLICATION_MEDIA_SUBLAYER; // -2
        case TYPE_APPLICATION_MEDIA_OVERLAY:
            return APPLICATION_MEDIA_OVERLAY_SUBLAYER; // -1
        case TYPE_APPLICATION_SUB_PANEL:
            return APPLICATION_SUB_PANEL_SUBLAYER; // 2
        case TYPE_APPLICATION_ABOVE_SUB_PANEL:
            return APPLICATION_ABOVE_SUB_PANEL_SUBLAYER; // 3
    }
    return 0;
}