That's one of the things I don't like about DipTrace. The rendering of the schematic in the editor is absolutely crap, eye straining and basically unacceptable in these days of OpenGL, Direct3D, DirectX and whatever. It should be trivial to get it right, right?
Any PC of reasonable vintage has immense processing power, so that can't be an excuse. The eighties and nineties are long gone, so cycle counting in the core drawing routines to get acceptable performance is something of the long gone past.
edit:
I think internally it rasterizes the schematic to a bitmap at a fixed scale, then downscale or upscale this image with a simple pixel skipping/duplication algorithm (not even bicubic interpolation), then draw the crappy result to the screen. The right way would be to rescale the vector data and rasterize that.