Some PC games let you drag the window edges and resize them to almost any dimensions, while others restrict windowed mode to a list of preset resolutions. Is this mainly a developer choice, or does supporting arbitrary window sizes require substantially more work? What changes in the game's rendering and UI code when the window size is dynamic?
3 Answers
Performance can matter too. A larger window generally means more pixels for the GPU to render, so resizing upward may reduce frame rate. However, that doesn’t usually explain why a game refuses arbitrary sizes; it can simply render at the new size and let performance vary. Fixed resolution options are often chosen because they’re easier to test and because some games, especially pixel-art titles, need special scaling to avoid blurry or uneven pixels.
Fullscreen and windowed modes can use different presentation paths, and the available resolutions may depend on the monitor, operating system, graphics API, and display mode. Still, modern engines are generally capable of rendering to a dynamically sized window. Whether players can resize it freely comes down to how the developers handled viewport updates, UI layout, aspect-ratio rules, and minimum or maximum window sizes.
It’s mostly an implementation choice, but arbitrary sizes do add complexity. The 3D rendering itself usually scales naturally: the game can update the viewport and render to the new dimensions. The harder part is the interface and layout. Menus, text, HUD elements, aspect ratios, camera framing, and split-screen views all need to behave sensibly at different widths, heights, and ultrawide formats. Developers may therefore support a minimum and maximum size, or provide only a tested list of resolutions to reduce bugs and testing work.
Exactly—rendering the scene is usually the straightforward part. Keeping every UI element readable and correctly positioned across unusual aspect ratios is where most of the extra work tends to be.