On computers, why is the mouse constrained in the left and top borders of the screen, but can go past the bottom and right border of the screen?
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It isn’t. It just that the mouse pointer is a 1×1 pixel and the image of the mouse cursor most often is on the upper left corner. If you change the mouse cursor to some centered icon, you’ll see the left and upper parts sticking out at the right and lower edges on the screen.
because the cursor is angled down and to the right. the tip of the cursor is the pixel you use to click, and that pixel is confined to the screen, but the actual shape of the cursor doesn’t need to be restricted in any way
I guess more accurately, the pixel you use to click needs to be able to hit the edges of your screen, so the cursor’s shape *needs* to be able to pass behind those edges
The constraint is on the point of the cursor where the click location is read. The rest of the pointer is just decoration to help you see it. Since the arrow extends from the bottom right to that point, it has to go off-screen in order to reach the full extents of the screen. If the entire cursor were constrained, the bottom and left edges of the screen would by unclickable.
The icon of the mouse pointer clicks on whatever is at the upper left point of the icon. If you’re trying to click on something on the far right side of the screen, or on the bottom of the screen, most of the icon has to disappear off of the screen in order for you to click those things.
Depending on your monitor you can usually see the left edge of the mouse pointer when you’re on the far right side of the screen, but you can’t see the top because it’s just a single point.
It’s because the tip of the mouse arrow on screen is where the mouse pointer is.
The rest of the arrow is just there so we can see it better.
So you can move the tip all the way to the edges of your screen in order to click stuff at or near those edges. On the left and top sides the rest of the arrow will be inside your screen and visible, on the right and bottom sides, the rest of the arrow is off screen and cannot be seen.
The mouse is constrained the same on all edges. The mouse itself is the very point of the arrow. The rest of the arrow just hangs off of this, and has no “collisions”.
Since the arrow hangs down and right, it disappears when the mouse is in the bottom right – the arrow hangs offscreen. When the mouse is up and left, the arrow hangs down and right; it hangs in the visible screen.
You can think of it like your screen is a box with walls, and your mouse hovers above the box. Then, there’s a long spike at the very tip of your mouse pointer that pokes down into the box.
If you move the mouse to the top left, the spike at the tip of the pointer hits the walls at the corner and keeps the mouse from moving any farther. Since the spike happens to be at the top left tip of the pointer arrow, none of the arrow goes off the screen.
If you drag it to the bottom right, the pointer is free to move off the screen, until the nail at the tip clips the corner. So it never *fully* goes off the screen, it just barely hangs on.
It’s not a very well-known feature, but you can actually change your mouse pointer to look like anything you want. The default happens to be an arrow with that imaginary spike lined up with the tip. But you could just as well go into the system settings and change it to, I dunno, a crosshair or a ring target, where the spike is in the dead center. Or if you’re masochistic, you can even keep the default pointer, but move the spike to the dead center of the arrow instead of the tip. If you had a pointer like one of those, then everything beyond the imaginary spike would go offscreen whenever you drag the pointer to one of the screen’s edges or corners. It’s just that singular point where the spike is that has to stay on the screen, the rest of it is just decoration.
Only the tip of the mouse pointer arrow is constrained.
And since the tip of the default pointer is on the upper left part of its arrow body, when you go to the top and left borders, the tip stays outside the border and so does the rest of the arrow.
But when you go to a bottom border, in order for the tip to reach the border, the rest of the arrow has to sink below.
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