Performance issue in CanvasCommandList with big Scale Transform

[mdmozibur]

I have a large numbe of geometries drawn into a CanvasCommandList.
Not all of it is being shown in the screen at the same time.
Moreover, I let the user zoom in.
I use scale transform into the CanvasDrawingSession to zoom in :

drawngSession.Transform = Matrix3x2.CreateScale(zoom_factor);

The issue is, if the zoom factor is much (100 or more), the FPS drops significantly. Please note that I use CanvasStrokeTransformBehavior.Fixed. I am assuming that the performance issue is because of the increased size of the commandList bound due to the large scale transform applied. In that case, how can mention a culling rectangle / avoid drawing the part of commandList that is outside of the visible bound?

I tried using PushLayer method of drawingSession, used the visible rectangle as the clipping rectangle. It did not change anything unfortunately. Please advice me in this situation here.

[getrou]

Hello, thanks for your question!

It's hard to nail down exactly what would cause your FPS drop at high zooms, but here are some ideas:

• More zoomed in means more pixels drawn, and even pixels drawn outside the render target have a cost.
• D2D increases the fidelity of some of its visuals as you zoom in, both in its logical scene and its anti-aliasing.

Those two things combined make for a big perf problem.

Some solutions:

1. PushLayer and clipping still happens on the GPU side and still incurs a perf cost. My first recommendation without knowing more is to do manual clipping. Is it an option to manually detect intersection with the visible rectangle and simply not issue those draw commands at the per-object level? I know you mentioned you are using CanvasCommandList, so I understand this might be difficult. If you go this route and haven't checked out CanvasVirtualControl, you might want to take a look, as it's good if you're only rendering to a subrect of your render target.
2. Try reducing the fidelity settings at high zooms. I'd start with CanvasAntialiasing, which controls the per-primitive antialiasing. This will help determine if the "higher fidelity at higher zooms" issue is a culprit here.