I made a tool in ruby. on mac mac book pro OSX with sketchup pro 2018, the line of my tool are cut with an invisible section plane like the cliping box of the graphic card.
It’s the getExtents method of the Tool interface that is used to determine the bounding box to render in.
By default the model bounding box is used, but as your new lines extend outside the bounding box they risk being clipped. If you let the getExtents method return a bounding box defined by the start and end of the frame, as well as its height, it should be fully drawn.