From 17dda3917d6d11e59c4f6df2c42bd3ce803eee6b Mon Sep 17 00:00:00 2001
From: Louai Al-Khanji <louai.al-khanji@digia.com>
Date: Thu, 8 May 2014 10:23:19 +0300
Subject: Direct2D QPA: Never queue more than one frame

Microsoft recommends setting the maximum frame latency to 1:

http://blogs.windows.com/windows/b/appbuilder/archive/2013/12/18/optimizing-directx-apps-for-low-latency-input-and-longer-battery-life.aspx
http://msdn.microsoft.com/en-us/library/windows/desktop/hh780339(v=vs.85).aspx

Apparently it slightly reduces power consumption and it also slightly
increases performance. So let's set it.

Change-Id: I8a540f1e54e83d6dc13f25564e10b751e202ce66
Reviewed-by: Risto Avila <risto.avila@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
---
 src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

(limited to 'src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp')

diff --git a/src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp b/src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp
index 1ea90c4f91..d757789935 100644
--- a/src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp
+++ b/src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp
@@ -90,7 +90,7 @@ public:
             return false;
         }
 
-        ComPtr<IDXGIDevice> dxgiDevice;
+        ComPtr<IDXGIDevice1> dxgiDevice;
         ComPtr<IDXGIAdapter> dxgiAdapter;
 
         hr = d3dDevice.As(&dxgiDevice);
@@ -99,6 +99,9 @@ public:
             return false;
         }
 
+        // Ensure that DXGI doesn't queue more than one frame at a time.
+        dxgiDevice->SetMaximumFrameLatency(1);
+
         hr = dxgiDevice->GetAdapter(&dxgiAdapter);
         if (FAILED(hr)) {
             qWarning("%s: Failed to probe DXGI Device for parent DXGI Adapter: %#x", __FUNCTION__, hr);
-- 
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