What factors determine DXGI_FORMAT?

Question

I am not familiar with directx, but I ran into a problem in a small project, part of which involves capturing directx data. I hope, below I make some sense.

General question:

I would like to know what factors determine the DXGI_FORMAT of a texture in the backbuffer (hardware?, OS?, application?, directx version?). And more importantly, when capturing a texture from the backbuffer, is it possible to receive a texture in the desired format by supplying the format as a parameter, having the format automatically converted if necessary.

Specifics about my problem :

I capture screens from games using Open Broadcaster Software(OBS) and process them using a specific library(OpenCV) prior to streaming. I noticed that, following updates to both Windows and OBS, I get 'DXGI_FORMAT_R10G10B10A2_UNORM' as the DXGI_FORMAT. This is a problem for me, because as far as I know OpenCV does not provide a convenient way for building an OpenCV object when colors are 10bits. Below are a few relevant lines from the modified OBS source file.

d3d11_copy_texture(data.texture, backbuffer);
...
hlog(toStr(data.format));  // prints 24 = DXGI_FORMAT_R10G10B10A2_UNORM
...
ID3D11Texture2D* tex;
bool success = create_d3d11_stage_surface(&tex);
if (success) {
    ...
    HRESULT hr = data.context->Map(tex, subresource, D3D11_MAP_READ, 0, &mappedTex);
    ...
    Mat frame(data.cy, data.cx, CV_8UC4, mappedTex.pData, (int)mappedTex.RowPitch); //This creates an OpenCV Mat object.
                                               //No support for 10-bit coors. Expects 8-bit colors (CV_8UC4 argument).
                                               //When the resulting Mat is viewed, colours are jumbled (Probably because 10-bits did not fit into 8-bits).

Before the updates (when I was working on this a year ago), I was probably receiving DXGI_FORMAT = DXGI_FORMAT_B8G8R8A8_UNORM, because the code above used to work.

Now I wonder what changed, and whether I can modify the source code of OBS to receive data with the desired DXGI_FORMAT.

'create_d3d11_stage_surface' method called above sets the DXGI_FORMAT, but I am not sure if it means 'give me data with this DXGI_FORMAT' or 'I know you work with this format, give me what you have'.

static bool create_d3d11_stage_surface(ID3D11Texture2D **tex)
{
    HRESULT hr;

    D3D11_TEXTURE2D_DESC desc      = {};
    desc.Width                     = data.cx;
    desc.Height                    = data.cy;
    desc.Format = data.format;
    ...

I hoped that, overriding the desc.Format with DXGI_FORMAT_B8G8R8A8_UNORM would result in that format being passed as argument in the ID3D11DeviceContext::Map call above, and I would get data with specified format. But that did not work.

DXGI_FORMAT of a texture is specified during the texture creation. You might need to "convert" the r10g10b10a2 data into b8r8g8a8 into the CPU when feeding it to OpenCV for processing. — VuVirt, Aug 11 '17 at 17:21
I checked directxtex but I think getting the image from another place within OBS will be easier in my case. — poster9238463, Aug 14 '17 at 12:57

score 3 · Accepted Answer · answered Aug 11 '17 at 19:59

3

The choice of render target is up to the application, but they need to pick one based on the Direct3D hardware feature level. Formats for render targets in swapchains are usually display scanout formats:

DXGI_FORMAT_R8G8B8A8_UNORM
DXGI_FORMAT_R8G8B8A8_UNORM_SRGB
DXGI_FORMAT_B8G8R8A8_UNORM
DXGI_FORMAT_B8G8R8A8_UNORM
DXGI_FORMAT_R10G10B10A2_UNORM
DXGI_FORMAT_R16G16B16A16_FLOAT
DXGI_FORMAT_R10G10B10_XR_BIAS_A2_UNORM (rare)

See the DXGI documentation for the full list of supported formats and usages by feature level.

Direct3D 11 does not do format conversions when you copy resources such as copying to staging render textures, so if you want to do a format conversion you'll need to handle that yourself. Note that CPU-side conversion code for all the DXGI formats can be found in DirectXTex.

answered Aug 11 '17 at 19:59

Chuck Walbourn

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So in my case it is the game that sets the format (based on hardware feature level.) – poster9238463 Aug 14 '17 at 12:54
@Chuck what about our textures? Do we have to consider the dxgi_format of our textures for the dxgi_format of our render target, or is it unrelated? Thanks. – KeyC0de Sep 30 '21 at 13:14
1

They are in general independent, with the exception of how you want to handle colorspaces. See [This GPU Gems 3 article](https://developer.nvidia.com/gpugems/gpugems3/part-iv-image-effects/chapter-24-importance-being-linear). – Chuck Walbourn Sep 30 '21 at 19:58

score 0 · Answer 2 · answered Aug 23 '17 at 14:41

It is the application that decides that format. The simplest one would be R8G8B8A8, which simply represents RGB and alpha values. But, if developer decides that he will be using HDR, the backbuffer would probably be R11B11G10, because you can store way more precise data there, without alpha channel information. If the game is for example black and white, there's no need to keep all RGB channels in the back buffer, you could use simpler format. I hope this helps.

What factors determine DXGI_FORMAT?

2 Answers2