UpperLeft

Upperleft is a term used in computing to denote the upper-left corner or origin of a two-dimensional coordinate space, rectangle, or image. In natural language it is usually written as “upper left” or “top left,” but in code and data structures it may appear as UpperLeft, upperleft, TL, or similar variants depending on the language or library. The concept is fundamental in defining positions, regions, and alignments in graphical contexts.

In most raster graphics and user interface frameworks, the origin of the coordinate system is at the upper-left corner of the canvas or window. The x coordinate increases to the right, while the y coordinate increases downward. This convention differs from many mathematical coordinate systems, where the origin is at the bottom-left and the y axis increases upward. Because of this, calculations for rendering, cropping, and hit-testing often reference the upper-left corner as the starting point.

Applications of the upper-left concept include defining bounding boxes, regions of interest, and layout anchors. For example, a rectangle can be described by the coordinates of its upper-left corner together with its width and height. Image processing routines frequently use the (0,0) coordinate to denote the upper-left pixel, with subsequent pixels identified relative to that origin.

Variants and related terms are common. The idea is often contrasted with lower-left, upper-right, or bottom-right corners. In programming, naming conventions for this concept vary by language and library, leading to identifiers such as UpperLeft, TopLeft, TL, or left/top coordinates. Understanding the upper-left origin is essential for correctly performing spatial calculations in most 2D graphics and UI systems.