Created attachment 118914 [details] Pics from comment I see it as a big tool with several possibilities. Two vanishing points(VP) are put on one line (horizon lines). After put the third point - the station point(SP). SP should be blocked and not moving. Ideally, the angle between two vanishing points and the station point should also be measured. What is it for. To draw boxes at different angles on the same plane in perspective, you need to have a SP from which the viewer is watching. The angle between two VP and SP should be 90 degrees. But this is for one box. To draw another you need other vanishing points at an angle of 90 degrees. (pic. 2) Now we have to move both VP manually. And something else to mark the station point And the way I imagine it. I use reference image with alpha png file (pic. 4) 1) Put one point, then another on the same line with the first. Then SP. 3 step (pic. 1) 2) The SP must be able to block the movement. 3) The angle can be shown near the station point or be in the panel. (pic. 3)
This is already implemented in Krita 5.0, for example in 6e3a7c7910. Please see https://krita-artists.org/t/call-for-testing-2-point-perspective-assistant/21751 if you want to look at the feature, or just test Krita Next, or wait until the beta phase to test Krita 5.0-beta version when it comes out in a month from now. If you have any improvements in mind, they should go to the KA forum thread as well.