Consider using reflection to optimize code paths in stock scenarios

WinForms is almost completely configurable but that comes at a performance cost. When we get windows messages (WM_*) we create event classes and jump through a lot of hoops that would not be necessary in a closed system.

For one example, getting a WM_ERASEBKGND often ends up being a FillRect on the passed in HDC. We could potentially avoid a lot of hoop jumping some allocations if we knew the OnPaintBackground was completely under our control.

We would pay up front for this sort of check, but could potentially earn it back quite quickly. The following code takes a couple of milliseconds on class creation:

Type type = GetType();
_isTypeInAssembly = type.Assembly == typeof(Control).Assembly;

_isOnPaintBackgroundLocal = _isTypeInAssembly
    || type.GetMethod(
        "OnPaintBackground",
        BindingFlags.NonPublic | BindingFlags.Instance,
        null,
        new Type[] { typeof(PaintEventArgs) }, null
             ).DeclaringType.Assembly == typeof(Control).Assembly;

If we find measurable situations where we go “if only we knew this wasn’t customized” this may be a strategy to attempt.

[RussKie]

As a disclaimer, this issue come up in our recent backlog triage, but this work is not high on our todo list, and we don’t expect any immediate actions here (at least form our side).

Thank you for your thoughts. I don’t think source generators would really work in this case - they are a “compile-time thing”, and at runtime descendant types may be dynamically loaded or generated (e.g., plugins). The other two approaches in theory sound plausible, though as you said, they carry own risks and limitations. But these may be a good start in the exploration of this problem space.

[kant2002]

I don’t think source generators would really work in this case

We can come up with something which works like ComWrappers. Each library can be responsible for their own drawing. But so far, this is theoretical exercise. Again, seems to be overkill, given that source generators has a price.