Large images

A GPU texture has a maximum side — 16384 on current integrated hardware, and as little as 2048 on the oldest cards nitid still runs on. A stitched panorama or a scanned map goes past it, and the way that failed is worth knowing: the graphics API has no way to return the rejection, so it reports it through a side channel and the default handling is a panic. Before this version such a file decoded all the way through and then took the viewer down at the moment it was about to appear.

nitid cuts such an image into tiles the device will hold and draws them as one picture. Zoom and pan work as they do on any other image, and the joins are invisible: each tile carries one pixel of its neighbour so the filter has a real texel to interpolate towards, rather than the repeated edge that leaves a visible step under magnification. An image that fits in one texture is still one texture and one draw call — tiling costs it a single comparison.

Still bounded by memory rather than by the texture limit: a tiled image holds every pixel at once. See ADR 0015.