C++ How to get layered window content image?

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C++ How to get layered window content image?

RL Chen 265

My goal is to get an HDC of an image or image of the contents of a layered window in Windows 7 and above.

I tried PrintWindow(hwndMag, hdcDest, PW_RENDERFULLCONTENT), but this requires Windows 8.1. Note that layered windows may contain transparency, or be obscured, and I need a solution that meets the above requirements, thanks!

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Answer 1

Castorix31 91,876

DwmRegisterThumbnail detects transparency

It can de drawn on a background with a given color (then I used D3DXSaveSurfaceToFileInMemory in an old test to get the resulting bitmap bits, but not sure if it is necessary...)

RL Chen 265 Reputation points

2024-05-17T23:36:51.86+00:00

@Castorix31 Thank you for your answer, but after reviewing the usage documentation of the two functions you provided, I still don't quite understand this approach. Can you provide a more detailed description or code?
Castorix31 91,876 Reputation points

2024-05-20T06:35:03.83+00:00

I re-tested my old test app and in fact, without PW_RENDERFULLCONTENT, D3DXSaveSurfaceToFileInMemory must be used on the rendered pixels (BitBlt does not work and D3D can save anything, but only what is displayed on screen)

I could post the sample, but if I want to save transparency, the resulting window must be displayed briefly to be saved by D3D, which is not great...

But do you really need Windows 7 compatibility, because it is not supported anymore since 2020 ?
RL Chen 265 Reputation points

2024-05-20T09:04:42.53+00:00

@Castorix31 Thanks for your reply, my plan is to intercept the image on a window with 0 transparency and then modify the image to be opaque to get the original image. But this window is not my program's own, I am trying to intercept what is drawn by another window, and that window has a transparency of 0 and may be occluded, so that means your method may not be appropriate, right? It would be nice if you could have another program or this program could solve this problem, but I would still like to have the exact code, thanks. As for why you need Windows 7 compatibility, as you know, 7 still has a high share and many users want to use this software on 7.
Castorix31 91,876 Reputation points

2024-05-20T10:25:06.3366667+00:00

I intercept and copy the window content in a popup window

It is just that to be compatible with Windows 7, this popup window must be displayed (a few ms) before getting the image with D3D, while on Windows 10 it can stay hidden
RL Chen 265 Reputation points

2024-05-20T10:27:48.3466667+00:00

Thanks for the reply, but I don't think it's realistic to need to show the window, thanks for the answer.
Castorix31 91,876 Reputation points

2024-05-20T10:28:14.31+00:00

Or for old OS (Vista, maybe Windows 7), there is this old method, a bit complicated : https://github.com/notr1ch/DWMCapture/tree/master

(does not work with Windows 10, even with DwmDxGetWindowSharedSurface (works with Notepad, but not with a window with transparency))
RL Chen 265 Reputation points

2024-05-20T10:31:40.6466667+00:00

So does this old solution support win8? If it's win8.1 I can use the PrintWindow function, if it's lower then this solution.
Castorix31 91,876 Reputation points

2024-05-20T10:34:59.44+00:00

I don't know for 8.0; for OS >= Win 8.1, PW_RENDERFULLCONTENT is the best method

(I tested on Windows 10, it can capture any window (except maybe DirectX games, not tested))
RL Chen 265 Reputation points

2024-05-20T10:42:45.4533333+00:00

Thanks for that, looks like I'll have to test 8.0, looks like it's been abandoned. Haha, that's funny~

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C++ How to get layered window content image?

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