I spend most of my time on networking, performance, and browser security issues, but while working on a test page recently, I came across some interesting behavior and cross-browser differences when using custom cursors in HTML content.
Web developers can choose which cursor is shown when hovering over HTML elements using the cursor property. There are a number of built-in cursors, or they can specify the URL of a Cursor (.cur) or Animated Cursor (.ani) file that should be downloaded and used.
When I specified that IE should use a cursor file containing a 16×16 image, however, I found that IE stretched it to 32×32. Similarly, I found that when I used a 64×64 image, IE scaled it down to 32×32. You’ll see the same scaling behavior for icons of size 20×20, 20×40, 128×128 and 256×256.
It turns out that IE passes the LR_DEFAULTSIZE flag when calling LoadImage on the cursor file, and that means that the image’s intrinsic size is ignored in favor of the default “system metrics” cursor size, which is 32×32 by default. Hence, IE will shrink or stretch cursors to match the size specified by the system metric.
Various browsers have different behaviors, which you can see in action on this test page.
- Opera 10.52 doesn’t support custom cursors at all.
- Internet Explorer 8 and below scales all cursors to 32×32.
- Firefox 3.6 shows 16×16 and 32×32 custom cursors at their native size and ignores other-sized cursors.
- Safari 4.05 shows 16×16, 20×20, 20×40, 32×32, and 64×64 custom cursors at their native size and ignores other-sized cursors.
- Firefox 3.7 and Chrome 4.1 show 16×16, 20×20, 20×40, 32×32, 64×64 and 128×128 custom cursors at their native size and ignore 256×256 cursors.
Update: Custom cursors are no longer scaled to 32×32 in IE9 Standards Mode.