Merge branch 'master' into temp-cocoa-scroll-acceleration-fix

Up until the 2.79 release, we'd use our own acceleration method for scrolling
on macOS. Since then we rely on macOS to do this for us, but turns out it does
a worse job, at least for our needs. This is an experiment to bring the old
behavior back.

intern/ghost/intern/GHOST_SystemCocoa.mm

@@ -1708,16 +1708,42 @@ GHOST_TSuccess GHOST_SystemCocoa::handleMouseEvent(void *eventPtr)
         double dx;
         double dy;
 
-        /* with 10.7 nice scrolling deltas are supported */
-        dx = [event scrollingDeltaX];
-        dy = [event scrollingDeltaY];
+        /* trying to pretend you have nice scrolls... */
+        dx = [event deltaX];
+        dy = [event deltaY];
+        if ((dx == 0) && (dy == 0))
+          break;
 
-        /* However, Wacom tablet (intuos5) needs old deltas,
-         * it then has momentum and phase at zero. */
-        if (phase == NSEventPhaseNone && momentumPhase == NSEventPhaseNone) {
-          dx = [event deltaX];
-          dy = [event deltaY];
+        const double deltaMax = 50.0;
+        /* Quadratic acceleration */
+        dx = dx * (fabs(dx) + 0.5);
+        if (dx < 0.0) {
+          dx -= 0.5;
         }
+        else {
+          dx += 0.5;
+        }
+        if (dx < -deltaMax) {
+          dx = -deltaMax;
+        }
+        else if (dx > deltaMax) {
+          dx = deltaMax;
+        }
+
+        dy = dy * (fabs(dy) + 0.5);
+        if (dy < 0.0) {
+          dy -= 0.5;
+        }
+        else {
+          dy += 0.5;
+        }
+        if (dy < -deltaMax) {
+          dy = -deltaMax;
+        }
+        else if (dy > deltaMax) {
+          dy = deltaMax;
+        }
+
         window->clientToScreenIntern(mousePos.x, mousePos.y, x, y);
 
         NSPoint delta = [[cocoawindow contentView] convertPointToBacking:NSMakePoint(dx, dy)];