Where does Wpf interface with DX?

[NWoodsman]

I would like to debug an issue outside the realm of PresentationCore, so I would like to know, for example, when a DependencyProperty is updated, where the call stack travels to arrive at the UI repainting.

My guess is at the Visual level, but I can't find it in source which leads me to think that Visual is a "managed" repainting i.e DrawingContext.RenderOpen is for clients whereas there is internal repainting with DirectX in some other assembly. Any ideas?

Ok, I have answered some of my questions. I'm going to update this thread with info to help you learn what I learn.

TLDR: PresentationCore => MIL ("Media Integration Layer") assemblies => Graphics assemblies.

I'm going to work through the example of drawing a single line.

Given a DrawingVisual, you call DrawingVisual.RenderOpen() which returns a DrawingContext object. This is actually a trick move for the API because DrawingContext is abstract with no public inheritance. What you actually get is an instance of RenderDataDrawingContext which is the only internal implementation of DrawingContext.

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/RenderDataDrawingContext.cs
src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Generated/RenderDataDrawingContext.cs

You publicly call DrawingContext.DrawLine(Pen,Point,Point) which is implemented in RenderDataDrawingContext. So the internal method opens an unsafe code block and creates a MIL struct MILCMD_DRAW_LINE from the above arguments.

An internal field _renderData of type RenderData is stored in RenderDataDrawingContext._renderData and the above unsafe code ends by calling _renderData.WriteDataRecord(MILCMD.MilDrawLine, (byte*)&record, 40); which I'm guessing is the buffer into which the pixels are painted. But this is as far as I got for now.