Wallpaper Engine costs almost nothing while a window covers it, and real frames while none does

That is the mechanism, and it is worth stating before any verdict, because the verdict changes with what you are doing and the mechanism does not. The program is only ever expensive while you can see it. The moment a game, a video player or a maximized window covers the desktop, the wallpaper stops rendering and its cost falls to the memory it is still holding.

The pause rule is the whole answer

The pause rule works on visibility, not on effort. Wallpaper Engine watches what is in front of the desktop and stops drawing when something covers it, which is why benchmark comparisons of a game with and without it running usually land within the noise of the test. Nothing clever is happening: there is simply no wallpaper being rendered during the measurement. The behavior is configurable, so a reader who has turned pausing off has turned off the reason the program is cheap.

Three states are worth telling apart, because people report wildly different numbers and are usually describing different states.

What the quality settings change while it is visible

The quality settings change what is drawn during the visible case, and the frame rate cap is the one that moves the number most. A wallpaper redrawn fewer times a second is doing proportionally less work, and a background you glance at between tasks does not need the same refresh as the thing you are looking at directly. Resolution scaling is the second lever: a scene rendered below the panel's native resolution and scaled up costs less, and on a wallpaper sitting behind a grid of icons the softening is genuinely hard to notice.

Which lever helps depends on the wallpaper type. A video wallpaper is decoded by the fixed function video block on the GPU, hardware that exists for exactly this and is otherwise idle, so it is cheap even at high resolution and barely responds to quality sliders. A scene or web wallpaper is rendered by the same 3D pipeline your game uses, so it competes directly, and it is the type where the frame rate cap earns its keep. Wallpaper Engine is a Steam program that plays both kinds, which is why a single answer about its performance impact has never been possible.

What a still wallpaper costs, which is almost nothing

A still wallpaper costs memory and no meaningful compute. The image is decoded once, uploaded to the GPU as a texture, and composited by the same desktop compositor that is already drawing your windows. Doubling the resolution of a still image roughly quadruples the memory it occupies, because area scales with both dimensions, but it does not create ongoing work. This is why the common worry, that a 3840 x 2160 wallpaper will slow down a machine that was fine with 1920 x 1080, does not survive contact with what actually happens. The 4K file has four times the pixels of the 1080p one, not twice, so it costs four times the memory, and that is the end of the effect.

Moving wallpaper is the opposite case. A live wallpaper is a video your device never stops playing, so its cost is continuous rather than paid once at login. The distinction between a still file and a moving one matters far more to a frame rate than the resolution of either.

What size a desktop wallpaper should be

A desktop wallpaper should be the exact pixel dimensions of the panel it is going on, or larger, and never smaller. Undersized is the only real failure state: a file with fewer pixels than the screen must be enlarged, and enlargement invents detail that was never captured, which on anime line art shows up as soft outlines and halos. Oversized is merely wasteful, because the operating system throws the extra pixels away on load.

Every row in that table is a separate export. The same picture is a different file on every panel listed there, and the ultrawide rows are where it bites hardest. Scale a 16:9 file to fill the width of a 3440 x 1440 screen and you keep about 74% of its height, so roughly 13% is cut off the top and the same off the bottom, taking whatever was composed there with it. Finding the picture is the easy part; finding it at a shape that survives the crop is the work.

Whether desktop resolution changes gaming performance

Desktop resolution does not change gaming performance on its own, because a fullscreen game renders at the resolution it is set to render at, not the one the desktop happens to be using. What the desktop resolution changes is the size of the compositor's own buffers and the amount of work done drawing windows, which is a cost you pay while you are on the desktop and stop paying when a game takes the display exclusively. The figure that matters for frame rate is the game's own render resolution, and no wallpaper of any kind participates in it once the game is in front.

Where to go next

DEVICESYour desktop, your phone and your tablet each want a different wallpaper fileWallpaper sizes by deviceWALLPAPER ENGINEWallpaper Engine is a Steam program that plays things on your desktopWallpaper Engine, explainedLIVE WALLPAPERA live wallpaper is a video your device never stops playingWhat it is and what it costs