Corner-pin mapping fits a projected image to a surface by dragging four independent corner handles

Corner pinning is the fundamental technique for aligning a projected quad to a physical surface. Each VPT layer shows four handles (the corners) that you drag in either the preview or the output window. Dragging one handle repositions that corner alone, producing trapezoidal or irregular quads; shift-drag moves the whole layer, alt-drag scales it. If you drag a corner across the midpoint of the layer you can lose control of it; ctrl-Z (undo) reverts the last move, but undo only works inside the preview/output windows, not the main interface. Corner-pin is the entry point to projection mapping — the minimum needed to make a rectangle of light land squarely on a real wall.

Examples

Create a layer, assign a source, then drag the four corner handles in the preview window until the quad lines up with a rectangle marked on a wall; use shift-drag to nudge the whole quad into place.

Assessment

Demonstrate corner-pinning a layer onto a rectangle on a real surface. What do you do if you accidentally drag a corner past the midpoint of the layer, and where must you be for undo to work?