March 2017

15:50
Sat
11
Mar 2017

How to change display mode using WinAPI?

If you write a graphics application or a game, you may want to make it fullscreen and set specific screen resolution. In DirectX there are functions for that, but if you use OpenGL or Vulkan, you need another way to accomplish that. I've researched the topic recently and I've found that Windows API supports enumerating display devices and modes with functions: EnumDisplayDevices, EnumDisplaySettings, as well as changing mode with function ChangeDisplaySettingsEx. It's a programatic access to more or less the same set of features that you can access manually by going to "Display settings" system window.

I've prepared an example C program demonstrating how to use these functions:

DisplaySettingsTest - github.com/sawickiap

First you may want to enumerate available Adapters. To do this, call function EnumDisplayDevices multiple times. Pass NULL as first parameter (LPCWSTR lpDevice). As the second parameter pass subsequent DWORD Adapter index, starting from 0. Enumeration should continue as long as the function returns BOOL nonzero. When it returns zero, it means there are no more Adapters and that Adapter with given index and any higher index could not be retrieved.

For each successfully retrieved Adapter, DISPLAY_DEVICE structure is filled by the function. It contains following members:

There is a second level: Adapters contain Display Devices. To enumerate them, use the same function EnumDisplayDevices, but this time pass Adapter DeviceName as first parameter. This way you will enumerate Display Devices inside that Adapter, described by the same structure DISPLAY_DEVICE. For example, my system returns DeviceName = "\\.\DISPLAY1\Monitor0", DeviceString = "Generic PnP Monitor".

The meaning and the difference between "Adapter" and "Display Device" is not fully clear to me. You may think that Adapter is a single GPU (graphics card), but it turns out not to be the case. I have a single graphics card and yet my system reports 6 Adapters, each having 0 or 1 Display Device. That can mean Adapter is more like a single monitor output (e.g. HDMI, DisplayPort, VGA) on the graphics card. This seems true unless you have two monitors running in "Duplicate" mode - then two Display Devices are reported inside one Adapter.

Then there is a list of supported Display Settings (or Modes). You can enumerate them in similar fashion using EnumDisplaySettings function, which fills DEVMODE structure. It seems that Modes belong to an Adapter, not a Display Device, so as first parameter to this function you must to pass DISPLAY_DEVICE::DeviceName returned by EnumDisplayDevices(NULL, ...), not EnumDisplaySettings(adapter.DeviceName, ...). The structure is quite complex, but the function fills only following members:

I have a single graphics card (AMD Radeon RX 480) with two Full HD (1920 x 1080) monitors connected. You can see example output of the program from my system here: ExampleOutput.txt.

To change display mode, use function ChangeDisplaySettingsEx.

The function returns DISP_CHANGE_SUCCESSFUL if display mode was successfully changed and one of other DISP_CHANGE_* constants if it failed.

To restore original display mode, call the function like this:

ChangeDisplaySettingsEx(targetDeviceName, NULL, NULL, 0, NULL);

Unfortunately, display mode changed in the way described here is not automatically restored after user switches to some other application (e.g. using Alt+Tab), like in DirectX fullscreen mode, but you can handle it yourself. Good news is that if you pass CDS_FULLSCREEN flag to ChangeDisplaySettingsEx, the previous mode is automatically restored by the system when your application exits or crashes.

Comments (0) | Tags: windows graphics | Author: Adam Sawicki | Share

00:13
Thu
09
Mar 2017

First Time on GDC

I came back from my first GDC. I've been dreaming about going there since my university years. My first impression? It's huge! It runs for so many days (Monday to Friday). There are so many talks, more than a dozen at same time, that you really need to choose carefully what is most interesting to you (and stand in a queue before the room, because if you come too late and the talk is very popular, there may be no free seats left).

As the world's largest event of this kind in the industry, it attracts best professionals and offers quality talks. This time there were sponsored talks from Amazon (about their engine Lumberyard), Facebook, Khronos, Google, NVIDIA, Unity, Intel, Microsoft, Oculus, AMD, Epic, ARM, Sony and others - basically every big company that deals with graphics, plus many other talks presented by individual developers. I was interested mostly in graphics programming, but of course there were many other topics covered, like artistic or business aspect of game development.

Expo was also big, with over 100 companies presenting their products, services and technologies. Big difference from Polish Pozna˝ Game Arena is that GDC is targeted to professionals only, which means there aren't such big crowds of people standing in long queues to be able to play any game. I've never played so much VR as on this expo :)

There were other attractions too, like indie game developers presenting their productions or retro zone with working computers from previous decades. So many things to do there! In addition to that, I've met many friends there, who either live in US or came from Poland just like me.

Entrance fee is high, with pass for main conference starting at $1000 up to $2400 (on-site for all access), aside from plane ticket to San Franscisco and hotel there, so it's hard to go there on your own, unless your company pays for it. But if only you have the opportunity, I think GDC is definitely worth visiting.

By the way, gamedev conferences planned for this year in Poland are:

I hope to visit them all :)

Gallery of my photos (mostly from San Francisco):

Comments (0) | Tags: events | Author: Adam Sawicki | Share

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