Which layout is ideal for a health bar that extends across the top of the screen?

A horizontal layout is ideal for a health bar that extends across the top of the screen because it takes advantage of the width of the display, allowing for a clear and unobstructed view of the player's health status. This layout aligns well with how most users expect health bars to be represented, giving immediate visual feedback as the health decreases or increases.

In a horizontal configuration, the bar can stretch seamlessly to fill the available space and can be easily understood as it corresponds to the typical reading direction in many cultures, enhancing usability. It also provides ample room for additional indicators such as numerical health values or status effects, which can be placed alongside or on top of the bar.

Other layouts like vertical, square, or diagonal can be less intuitive for displaying a health status across the top, as they may restrict visibility or not utilize the space effectively, leading to a less user-friendly experience.