PlatformMouseEvent should use floating-point-precision, so that SVG hit detection can be floating point precise across scaled elements. I'll attach an example to show the current integer-only behavior.
Created attachment 10267 [details] This example shows the current integer-only behavior limiting proper hit-testing The goal of this bug is to change the behavior so that float/double mouse coordinates are maintained all the way through the engine until the final hit-testing in the render tree. Eventually if http://bugzilla.opendarwin.org/show_bug.cgi?id=10599 is also fixed than these floating-point mouse coordinates will also be exposed to JavaScript.
Created attachment 10268 [details] Fixed test case
I am able to reproduce this bug in Safari 15.5 on macOS 12.4 using attached "Fixed Test Case". While hovering the mouse (on laptop), all other browsers show odd numbers as well like 54,73 etc. and I can increment with precise movements on touchpad to go 73,74,75 but in case of Safari, it just jumps to 74,76 etc. (It is not precise and increments in double digit). If I am testing it incorrectly, please test accordingly. Thanks!