Add advanced setting to make scroll wheel response very sensitive.

sources/PTYScrollView.m

@@ -25,6 +25,7 @@
 #import "iTerm.h"
 #import "FutureMethods.h"
+#import "iTermAdvancedSettingsModel.h"
 #import "PreferencePanel.h"
 #import "PTYScrollView.h"
 #import "PTYTextView.h"
@@ -155,7 +156,15 @@ static CGFloat RoundTowardZero(CGFloat value) {
     if (theEvent.hasPreciseScrollingDeltas) {
         delta /= self.verticalLineScroll;
     }
-
+    if ([iTermAdvancedSettingsModel sensitiveScrollWheel]) {
+        if (delta > 0) {
+            return ceil(delta);
+        } else if (delta < 0) {
+            return floor(delta);
+        } else {
+            return 0;
+        }
+    }
     PTYScroller *verticalScroller = (PTYScroller *)[self verticalScroller];
     verticalScroller.accumulatedDeltaY += delta;
     CGFloat amount = 0;

sources/iTermAdvancedSettingsModel.h

@@ -193,5 +193,6 @@
 + (BOOL)lowFiCombiningMarks;
 + (CGFloat)verticalBarCursorWidth;
 + (BOOL)statusBarIcon;
++ (BOOL)sensitiveScrollWheel;
 @end

sources/iTermAdvancedSettingsModel.m

@@ -106,6 +106,7 @@ DEFINE_BOOL(alwaysAcceptFirstMouse, NO, @"Mouse: Always accept first mouse event
 DEFINE_BOOL(doubleReportScrollWheel, NO, @"Mouse: Double-report scroll wheel events to work around tmux scrolling bug.");
 DEFINE_BOOL(stealKeyFocus, NO, @"Mouse: When Focus Follows Mouse is enabled, steal key focus even when inactive.");
 DEFINE_BOOL(cmdClickWhenInactiveInvokesSemanticHistory, NO, @"Mouse: ⌘-click in an active pane while iTerm2 isn't the active app invokes Semantic History.\nBy default, iTerm2 respects the OS standard that ⌘-click in an app that doesn't have keyboard focus behaves like a non-⌘ click that does not raise the window.");
+DEFINE_BOOL(sensitiveScrollWheel, NO, @"Mouse: Scroll on any scroll wheel movement, no matter how small?");
 #pragma mark Terminal
 DEFINE_BOOL(traditionalVisualBell, NO, @"Terminal: Visual bell flashes the whole screen, not just a bell icon.");