Sorry, I forgot to add the title
How to Implement the Logic for Mixing DirectComposition with GDI?
On Tue, Jun 3, 2025 at 5:02 PM zhengxianwei baikaishiuc@gmail.com wrote:
Hello,
I would like to implement part of the logic within dcomp.dll in order to properly support applications that depend on it.
I found that Zhiyi Zhang has implemented some data structures and interface stubs:
https://gitlab.winehq.org/zhiyi/wine/-/commits/directcomposition?ref_type=he...
Among these, the only method with actual logic appears to be IDCompositionDevice::Commit.
However, after reviewing the implementation, I suspect there may be an issue with the current approach.
It seems that Zhiyi Zhang starts a separate thread for each IDCompositionDevice, and this thread runs at a fixed refresh rate.
But this approach appears to introduce a problem: from the window's (HWND) perspective, there are now *two threads* concurrently updating its device context.
This results in a frame sequence similar to the following (note: the frame intervals are illustrative only):
gdi_frame | dcomp_frame | gdi_frame | gdi_frame | dcomp_frame
In this model, GDI-generated frames and DComp-generated frames are interleaved.
Is my understanding correct?
If so, I believe this method may lead to *inaccurate rendering results*, although I am not entirely certain about the exact consequences (as I am not an expert in this area).
Therefore, I have decided to pursue an approach that produces a *standardized frame stream* like the following:
gdi_mix_dcomp_frame | gdi_mix_dcomp_frame | gdi_mix_dcomp_frame
In other words, I plan to merge GDI and DComp content before presenting each frame, ensuring consistency in the final output.
I’ve reviewed the normal GDI frame refresh process, and it seems to follow this path:
--> flush_window_surfaces --> window_surface_flush --> x11drv_surface_flush
I’m planning to insert the following logic inside x11drv_surface_flush:
if (is_hwnd_bind_to_dcomp(hwnd)) { struct Surface *final = get_comp_surface(hwnd);
blend_dcomp_surface_over_gdi(dest_surface, final);}
However, there’s still a question regarding *how to access the DComp data* inside x11drv_surface_flush.
One option is to do the composition inside IDCompositionDevice::Commit() like this: void IDCompositionDevice_Commit() { composite_proc(); ... ... push_frame_to_x11drv();
}
Another option is to *directly call into DComp APIs from within x11drv* to retrieve the surface data on demand.
However, *both approaches feel somewhat unnatural*, and from what I can tell, Windows seems to establish some kind of *internal channel* to pass the composed content to the compositor.
Is there a better or more canonical way to do this?
Any suggestions or guidance would be greatly appreciated.