I'm painting two layers of graphs on one CustomPaint. The first will occlude over half of the second layer.

Problem

Currently I just paint the first data and then second data using two Paints, with their blendMode set.

This creates an overlay of two data, which blends. But I don't need the blend, just the area of difference to be painted using the second Paint, i.e., a complementary composite view.

On the performance side, I don't know if blending would have internal optimization to avoid drawing the occluded part.

Reference image

Notice that all these data graphs blend but I just need them to occlude each other, while the overlapped parts don't draw at all for performance.

Attempts

I could use a new path to only draw the difference, but I'm not sure this is the easiest way.

I checked RepaintBoundary but it's a widget that handles infrequent data changes, not exactly what I need here.

Similarly Overlay seems a standalone widget, so I don't know how to fit it into CustomPaint.

Question

Is there a standard way to achieve the occlusion I need?