macOS: Fix touch scrolling sensitivity low on retina screens

Fixes #1112

docs/changelog.rst

@@ -43,6 +43,8 @@ Changelog
 
 - macOS: Use the system default double click interval (:pull:`1090`)
 
+- macOS: Fix touch scrolling sensitivity low on retina screens (:iss:`1112`)
+
 - Linux: Fix match rules used as aliases in Fontconfig configuration not being
   respected (:iss:`1085`)
 

glfw/cocoa_window.m

@@ -902,6 +902,11 @@ is_ascii_control_char(char x) {
     deltaX = [event scrollingDeltaX];
     deltaY = [event scrollingDeltaY];
     int flags = [event hasPreciseScrollingDeltas] ? 1 : 0;
+    if (flags) {
+        float xscale = 1, yscale = 1;
+        _glfwPlatformGetWindowContentScale(window, &xscale, &yscale);
+        if (yscale > 0) deltaY *= yscale;
+    }
 
     if (fabs(deltaX) > 0.0 || fabs(deltaY) > 0.0)
         _glfwInputScroll(window, deltaX, deltaY, flags);