変換対象領域が小さいのにモニタサイズより大きいフレームバッファサイズが必要なのはなぜですか？

画面の左右の上100ピクセルを削除するために変換を使用してみました1366x768（下記参照）xrandr。しかし、フレームバッファサイズが不足しているというエラーが発生します。

$ xrandr --output LVDS1 --fb 1366x768 --transform 1.171527,0.152543,-117.152659,0.000000,1.171527,0.000000,0.000000,0.000223,1.000000
xrandr: specified screen 1366x768 not large enough for output LVDS1 ( 1602x773+-118+0)

だからメッセージに言及されたサイズでサイズアップしました1602x773！それは動作します：

xrandr --output LVDS1 --fb 1602x773 --transform 1.171527,0.152543,-117.152659,0.000000,1.171527,0.000000,0.000000,0.000223,1.000000

この追加領域は何1366x5+236x768+236x5で、なぜ必要なのですか？ ！

変換対象領域が元の領域（元の画面サイズ）より小さいです！まあ、私はそれらが同じ長方形の面積を持っていると言うことができます。

ハードウェア、ドライバ、またはxorg関連の可能性があるため、ここに現在の設定を追加しました。

### Background Info

Ubuntu 15.10

X.Org X Server 1.17.2
Release Date: 2015-06-16
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.13.0-68-generic x86_64 Ubuntu
Current Operating System: Linux BlueSkies 4.2.0-25-generic #30-Ubuntu SMP Mon Jan 18 12:31:50 UTC 2016 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.2.0-25-generic root=UUID=9f0530d5-e0eb-43fa-b99b-000fa742cf10 ro persistent quiet splash vt.handoff=7
Build Date: 12 November 2015  05:33:29PM
xorg-server 2:1.17.2-1ubuntu9.1 (For technical support please see http://www.ubuntu.com/support) 
Current version of pixman: 0.32.6
    Before reporting problems, check http://wiki.x.org
    to make sure that you have the latest version.

xrandr program version       1.4.3
Server reports RandR version 1.4

  *-display               
       description: VGA compatible controller
       product: 3rd Gen Core processor Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 09
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:27 memory:f6400000-f67fffff memory:e0000000-efffffff ioport:f000(size=64)

### Base info

Screen 0: minimum 8 x 8, current 1366 x 768, maximum 32767 x 32767
LVDS1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
   1366x768      60.07*+  40.02  
   1360x768      59.80    59.96  
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   680x384       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

disable_display  N
disable_power_well  1
disable_vtd_wa  N
edp_vswing  0
enable_cmd_parser  1
enable_execlists  0
enable_fbc  -1
enable_hangcheck  Y
enable_ips  1
enable_ppgtt  1
enable_psr  0
enable_rc6  3
fastboot  N
invert_brightness  0
load_detect_test  N
lvds_channel_mode  0
lvds_downclock  0
lvds_use_ssc  -1
mmio_debug  0
modeset  -1
nuclear_pageflip  N
panel_ignore_lid  1
prefault_disable  N
preliminary_hw_support  0
reset  Y
semaphores  -1
use_mmio_flip  0
vbt_sdvo_panel_type  -1
verbose_state_checks  Y