Avatar-anchored Screen-scrolling
In 2D computer games Avatar-anchored screen-scrolling refers to screen-scrolling that is anchored to the avatar's position; that is, the viewport only scrolls (updates) when the avatar moves. Thus, the vision radius of the avatar is restricted to the current viewport. As well, the avatar's position is almost always viewport-centered.
Avatar-anchored screen-scrolling is contrasted with avatar-anchorless screen-scrolling.
In graphics terms, the avatar or impersonal unit controlled by the player is generally referred to as a sprite. However, an avatar can be represented by as little as a single character (a letter, number or symbol) or a single pixel. Indeed, an avatar need not be graphically represented at all.
Avatar-anchored scrolling can be icon-driven, mouse-movement driven, joystick-driven or keyboard-driven (arrow keys, numpad, wasd etc.)
An example of an avatar-anchored computer game is Diablo: the screen scrolls only when the controlled character (the avatar) is moved.
In turn-based computer games screen-scrolling can be anchored to AI-controlled units during the AI's turn.
Avatar-anchored scrolling is employed primarily in arcade-action computer games and solitaire-avatar computer games; that is, in computer games in which the player directly controls only one avatar. In rare cases scrolling can be anchored to avatar-groups (unit formations).
Depending on the genre in question avatar-anchored scrolling is more immersive than avatar-anchorless scrolling because the vision radius is restricted to the current viewport.
Historically, avatar-anchored scrolling has been smoother than avatar-anchorless scrolling by virtue of 50 FPS per-pixel hardware scrolling routines that tap into custom chips / VGA. However, rare examples exist of smooth avatar-anchorless scrolling even though such is dependent on manual player input, but in the vast majority of cases this is simply not true, even after the Advent of APIs.
Indeed, Diablo's release coincided with the advent of APIs yet Diablo's scrolling is not super-smooth. Thus, since it is an arcade-action computer game Diablo has rightly been penalized in Diablo's Place in 1990s Computer Game History.
I detected Diablo's lousy scrolling routine in one second flat back in 1996 -- as soon as I moved the avatar. Everyone with eyes that could see did.
So many people go on about how great Diablo's graphics were for 1996, yet it didn't even have smooth scrolling like many 8 bit computer games from the 1980s. In arcade-action games artistry doesn't mean a damn thing if the scrolling isn't smooth. And it doesn't matter that an unofficial mod came out 30 years later that updated the scrolling on PCs that are 1,000 times more powerful than what Diablo was coded for: that just isn't interesting, at all.
For more info on that largely ignored but highly relevant topic, refer to the section entitled The Advent of High Performance VGA Modes in History of 1990s Computer Games.
Note that screen-scrolling can also be anchored to interactable objects or core-gameplay objects. For example, in English football computer games it is not the currently controlled football player to which screen-scrolling is anchored but rather the football itself: the viewport updates (scrolls) based on football position, not player position. And the controlled player changes based on the proximity of the players to the football. It is a technical feat that EFCGs maintain ultra-smooth scrolling under frequent and sudden changes in direction.
cf.:
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