Only grab the full-screen image once, not per damage rect.

BUG=None
TEST=Dragging a large window around isn't glacially slow.
(ensure "xdpyinfo -ext MIT-SHM" shows SHM enabled, with no pixmap support)

Review URL: http://codereview.chromium.org/6905110

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83434 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 19 insertions, 7 deletions

diff --git a/remoting/host/capturer_linux.cc b/remoting/host/capturer_linux.cc
index 6aaff4e..2c5a2d7 100644
--- a/remoting/host/capturer_linux.cc
+++ b/remoting/host/capturer_linux.cc
@@ -288,6 +288,7 @@ void CapturerLinux::CaptureRects(
     }
   }
 
+  x_server_pixel_buffer_.Synchronize();
   for (InvalidRects::const_iterator it = rects.begin();
        it != rects.end();
        ++it) {
diff --git a/remoting/host/x_server_pixel_buffer.cc b/remoting/host/x_server_pixel_buffer.cc
index b93c40f..ae2a016 100644
--- a/remoting/host/x_server_pixel_buffer.cc
+++ b/remoting/host/x_server_pixel_buffer.cc
@@ -136,6 +136,15 @@ void XServerPixelBuffer::DestroyShmSegmentInfo() {
   }
 }
 
+void XServerPixelBuffer::Synchronize() {
+  if (shm_segment_info_ && !shm_pixmap_) {
+    // XShmGetImage can fail if the display is being reconfigured.
+    gdk_error_trap_push();
+    XShmGetImage(display_, root_window_, x_image_, 0, 0, AllPlanes);
+    gdk_error_trap_pop();
+  }
+}
+
 uint8* XServerPixelBuffer::CaptureRect(const gfx::Rect& rect) {
   if (shm_segment_info_) {
     if (shm_pixmap_) {
@@ -143,18 +152,11 @@ uint8* XServerPixelBuffer::CaptureRect(const gfx::Rect& rect) {
                 rect.x(), rect.y(), rect.width(), rect.height(),
                 rect.x(), rect.y());
       XSync(display_, False);
-    } else {
-      // XShmGetImage can fail if the display is being reconfigured.
-      gdk_error_trap_push();
-      XShmGetImage(display_, root_window_, x_image_, 0, 0, AllPlanes);
-      gdk_error_trap_pop();
     }
     return reinterpret_cast<uint8*>(x_image_->data) +
         rect.y() * x_image_->bytes_per_line +
         rect.x() * x_image_->bits_per_pixel / 8;
   } else {
-    // XGetSubImage would allow cleaner code here, (in particular,
-    // CaptureComplete could be removed) but XGetImage is faster.
     if (x_image_)
       XDestroyImage(x_image_);
     x_image_ = XGetImage(display_, root_window_, rect.x(), rect.y(),
diff --git a/remoting/host/x_server_pixel_buffer.h b/remoting/host/x_server_pixel_buffer.h
index e27b9f7..9ab03bf 100644
--- a/remoting/host/x_server_pixel_buffer.h
+++ b/remoting/host/x_server_pixel_buffer.h
@@ -25,9 +25,18 @@ class XServerPixelBuffer {
 
   void Init(Display* display);
 
+  // If shared memory is being used without pixmaps, synchronize this pixel
+  // buffer with the root window contents (otherwise, this is a no-op).
+  // This is to avoid doing a full-screen capture for each individual
+  // rectangle in the capture list, when it only needs to be done once at the
+  // beginning.
+  void Synchronize();
+
   // Capture the specified rectangle and return a pointer to its top-left pixel
   // or NULL if capture fails. The returned pointer remains valid until the next
   // call to CaptureRect.
+  // In the case where the full-screen data is captured by Synchronize(), this
+  // simply returns the pointer without doing any more work.
   uint8* CaptureRect(const gfx::Rect& rect);
 
   // Return information about the most recent capture. This is only guaranteed