The Viewport Trap: Preventing Geometry Corruption in Image Editors

Image editors often make a critical mistake by mixing the viewport layer (for comfortable viewing and interaction) with the actual image coordinates (needed for export). This causes the UI to look correct while the exported result is geometrically wrong—a subtle bug that compounds during resizing operations. Developers building crop editors, screenshot tools, and markup applications must maintain a clear boundary between these two coordinate systems to ensure reliable output.