disable crtcs bigger than new screen size during mode switch

ui/display/chromeos/x11/native_display_delegate_x11.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/display/chromeos/x11/native_display_delegate_x11.h"
 
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
 #include <X11/extensions/dpms.h>
 #include <X11/extensions/Xrandr.h>
@@ skipping 279 matching lines @@
 
 void NativeDisplayDelegateX11::CreateFrameBuffer(const gfx::Size& size) {
   CHECK(screen_) << "Server not grabbed";
   int current_width = DisplayWidth(display_, DefaultScreen(display_));
   int current_height = DisplayHeight(display_, DefaultScreen(display_));
   VLOG(1) << "CreateFrameBuffer: new=" << size.width() << "x" << size.height()
           << " current=" << current_width << "x" << current_height;
   if (size.width() == current_width && size.height() == current_height)
     return;
 
-  DestroyUnusedCrtcs();
+  DestroyUnusedCrtcs(size);
   int mm_width = size.width() * kPixelsToMmScale;
   int mm_height = size.height() * kPixelsToMmScale;
   XRRSetScreenSize(
       display_, window_, size.width(), size.height(), mm_width, mm_height);
   // We don't wait for root window resize, therefore this end up with drawing
   // in the old window size, which we care during the boot.
   DrawBackground();
 
   // Don't redraw the background upon framebuffer change again. This should
   // happen only once after boot.
@@ skipping 200 matching lines @@
   XRRChangeOutputProperty(
       display_, output_id, name, XA_ATOM, 32, PropModeReplace, data, 1);
   if (err_tracker.FoundNewError()) {
     LOG(ERROR) << "XRRChangeOutputProperty failed";
     return false;
   } else {
     return true;
   }
 }
 
-void NativeDisplayDelegateX11::DestroyUnusedCrtcs() {
+void NativeDisplayDelegateX11::DestroyUnusedCrtcs(const gfx::Size& new_size) {
   CHECK(screen_) << "Server not grabbed";
   // Setting the screen size will fail if any CRTC doesn't fit afterwards.
   // At the same time, turning CRTCs off and back on uses up a lot of time.
   // This function tries to be smart to avoid too many off/on cycles:
   // - We disable all the CRTCs we won't need after the FB resize.
   // - We set the new modes on CRTCs, if they fit in both the old and new
   //   FBs, and park them at (0,0)
   // - We disable the CRTCs we will need but don't fit in the old FB. Those
   //   will be reenabled after the resize.
   // We don't worry about the cached state of the outputs here since we are
@@ skipping 12 matching lines @@
       DisplaySnapshotX11* x11_output = static_cast<DisplaySnapshotX11*>(*it);
       if (crtc == x11_output->crtc()) {
         mode_info = x11_output->current_mode();
         output = x11_output->output();
         break;
       }
     }
 
     if (mode_info) {
       mode = static_cast<const DisplayModeX11*>(mode_info)->mode_id();
-      // In case our CRTC doesn't fit in our current framebuffer, disable it.
+      // In case our CRTC doesn't fit in common area of our current and about
+      // to be resized framebuffer, disable it.
       // It'll get reenabled after we resize the framebuffer.
-      int current_width = DisplayWidth(display_, DefaultScreen(display_));
-      int current_height = DisplayHeight(display_, DefaultScreen(display_));
-      if (mode_info->size().width() > current_width ||
-          mode_info->size().height() > current_height) {
+      int max_width = std::min(DisplayWidth(display_,
+                               DefaultScreen(display_)), new_size.width());

[Daniel Kurtz, 2014/04/25 04:35:29]

I think this would have been easier to read:
  int current_width = DisplayWidth(display_, DefaultScreen(display_));
  int common_width = std::min(current_width, new_size.width());

+      int max_height = std::min(DisplayHeight(display_,
+                                DefaultScreen(display_)), new_size.height());
+      if (mode_info->size().width() > max_width ||
+          mode_info->size().height() > max_height) {
         mode = None;
         output = None;
         mode_info = NULL;
       }
     }
 
     ConfigureCrtc(crtc, mode, output, 0, 0);
   }
 }
 
@@ skipping 101 matching lines @@
   XSetForeground(display_, gc, color.pixel);
   XSetFillStyle(display_, gc, FillSolid);
   int width = DisplayWidth(display_, DefaultScreen(display_));
   int height = DisplayHeight(display_, DefaultScreen(display_));
   XFillRectangle(display_, window_, gc, 0, 0, width, height);
   XFreeGC(display_, gc);
   XFreeColors(display_, colormap, &color.pixel, 1, 0);
 }
 
 }  // namespace ui