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I have a few questions regarding the Desktop Window Manager (aka DWM) in Windows 10:

Background: For an OpenGL application I wrote in C++ I need precise timing regarding the swap of the front and back buffers in OpenGL and the realization of these commands on the OS level. (I know Windows 10, or Windows in general, is a bad choice for this, but there are other limiting factors).

  • Question 1: My internet research showed that the DWM manages a third buffer (making visualization a triple buffered system) which I cannot control and therefore creates an unpredictable delay. The investigation also showed that this can be bypassed by opening an OpenGL context in fullscreen mode. Is this information correct?

  • Question 2: Is this delay caused by the fact that the OS randomly instructs the DWM to copy the buffer?

  • Question 3: How long is the actual delay, my investigation showed numbers between < 1ms and up to 50ms, but there was no trustworthy source.

In fact, besides for the single fact, the mere existence of the delay, there was no trustworthy source for any of the other assumptions which I was able to find on the internet. Therefore I kindly ask anyone having an answer to this questions to include if this possible, a reference to their statement.

I don't know if this is important, but I'm using OpenGL via GLFW and GLEW.

genpfault
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1 Answers1

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Although I was unable to find an answer to question 2 and 3, contacting the Nvidia support provided the answer to question 1.

Nvidia statet that an application rendered in a full screen context cannot access the DWM. Only applications rendered in windowed mode are handled by it.

Warning: They also said that this was by design. Considering the fact that Microsoft attempts to force users/programmers to use the DWM there is no guarantee on how long this design decision will remain unchanged.

Original mail from Nvidia:

[...]

After checking your request with our specialized department, please note that when a game or anything is in Full Screen you cannot access this Windows Feature [annot.: DWM]. This is by design. It needs to be windowed mode if you want to access this feature.

[...]

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