A full-bleed canvas backdrop built from one piece of classical geometry: a pencil of circles that all touch the same horizontal line across the middle of the stage, swept by advancing a single angle. Because every circle is tangent to that one line, the whole field is pinched into a bright seam with two focal points out at the sides, and the arcs splay away above and below it. The sweep runs the angle through a tangent, which is what opens the spacing out -- dense and almost flat near the seam, vast and sparse towards the edges -- so the field reads as depth rather than as a fan of evenly spread lines. Brightness is keyed to the size of each circle, so the near-flat ones carry the seam and the tight ones fall away into the dark; the glow control widens how much of the field is lit rather than raising the opacity of everything at once. Tilt biases the tangent, which slides the seam up and down the stage instead of rotating the picture, and the pointer drives the same bias across the same range, so a value set by hand and one set by the pointer behave identically -- useful for stages that are never hovered. The engineering the effect needs to survive is in place: the arcs that leave the stage are solved analytically and drawn only where they are actually visible, rather than drawing a full turn and letting the clip throw it away, and a circle that diverges past half a million pixels is drawn as the straight rule it has become instead of being handed to a rasteriser that may disagree about it. Phase advances on elapsed time normalised to 60Hz, so the sweep runs at the same speed on a 60Hz laptop and a 144Hz monitor and a backgrounded tab resumes where it left off. The canvas is device-pixel-ratio aware, stops drawing entirely when it scrolls out of view or the tab is hidden, thins its density on narrow stages, holds still under prefers-reduced-motion, and sits on nothing at all by default -- the stage is transparent, so the field composites over whatever is behind it, with a solid colour available as a setting rather than as the starting point. Line count, weight, colour, glow, speed, resting tilt and pointer response are all editable, and the export is one self-contained HTML file with no dependencies at all.
Effect · HTML / CSS / JS · All tools