Improve zooming with trackpad and scrollwheel

On macOS actual scroll delta is used for the zoom amount.
On Windows WHEEL_DELTA is used to allow smooth scrolling if supported.
Shift+Scroll is added for 10x finer zooming.

CHANGELOG.md

@@ -113,6 +113,7 @@ Other new features:
     that are shortcuts to the respective configuration screens.
   * New cmake build options using -DENABLE_OPENMP=yes and -DENABLE_LTO=yes
     to enable support for multi-threading and link-time optimization.
+  * "Shift+Scroll" for ten times finer zoom.
 
 Bugs fixed:
   * Fixed broken --view options for command line thumbnail image creation.

src/mouse.cpp

@@ -877,7 +877,6 @@ bool GraphicsWindow::ConstrainPointByHovered(hEntity pt, const Point2d *projecte
 
 bool GraphicsWindow::MouseEvent(Platform::MouseEvent event) {
     using Platform::MouseEvent;
-
     double width, height;
     window->GetContentSize(&width, &height);
 
@@ -918,7 +917,7 @@ bool GraphicsWindow::MouseEvent(Platform::MouseEvent event) {
             break;
 
         case MouseEvent::Type::SCROLL_VERT:
-            this->MouseScroll(event.x, event.y, (int)event.scrollDelta);
+            this->MouseScroll(event.x, event.y, event.shiftDown ? event.scrollDelta / 10 : event.scrollDelta);
             break;
 
         case MouseEvent::Type::LEAVE:
@@ -1472,18 +1471,25 @@ void GraphicsWindow::EditControlDone(const std::string &s) {
     }
 }
 
-void GraphicsWindow::MouseScroll(double x, double y, int delta) {
+void GraphicsWindow::MouseScroll(double x, double y, double delta) {
     double offsetRight = offset.Dot(projRight);
     double offsetUp = offset.Dot(projUp);
 
     double righti = x/scale - offsetRight;
     double upi = y/scale - offsetUp;
 
-    if(delta > 0) {
-        scale *= 1.2;
-    } else if(delta < 0) {
-        scale /= 1.2;
-    } else return;
+    // The default zoom factor is 1.2x for one scroll wheel click (delta==1).
+    // To support smooth scrolling where scroll wheel events come in increments
+    // smaller (or larger) than 1 we do:
+    //     scale *= exp(ln(1.2) * delta);
+    // to ensure that the same total scroll delta always results in the same
+    // total zoom irrespective of in how many increments the zoom was applied.
+    // For example if we scroll a total delta of a+b in two events vs. one then
+    //     scale * e^a * e^b == scale * e^(a+b)
+    // while
+    //     scale * a * b != scale * (a+b)
+    // So this constant is ln(1.2) = 0.1823216 to make the default zoom 1.2x
+    scale *= exp(0.1823216 * delta);
 
     double rightf = x/scale - offsetRight;
     double upf = y/scale - offsetUp;

src/platform/guigtk.cpp

@@ -472,7 +472,7 @@ protected:
     }
 
     bool process_pointer_event(MouseEvent::Type type, double x, double y,
-                               guint state, guint button = 0, int scroll_delta = 0) {
+                               guint state, guint button = 0, double scroll_delta = 0) {
         MouseEvent event = {};
         event.type = type;
         event.x = x;
@@ -536,7 +536,7 @@ protected:
     }
 
     bool on_scroll_event(GdkEventScroll *gdk_event) override {
-        int delta;
+        double delta;
         if(gdk_event->delta_y < 0 || gdk_event->direction == GDK_SCROLL_UP) {
             delta = 1;
         } else if(gdk_event->delta_y > 0 || gdk_event->direction == GDK_SCROLL_DOWN) {

src/platform/guimac.mm

@@ -554,7 +554,9 @@ MenuBarRef GetOrCreateMainMenu(bool *unique) {
 
     MouseEvent event = [self convertMouseEvent:nsEvent];
     event.type = MouseEvent::Type::SCROLL_VERT;
-    event.scrollDelta = [nsEvent deltaY];
+
+    bool isPrecise = [nsEvent hasPreciseScrollingDeltas];
+    event.scrollDelta = [nsEvent scrollingDeltaY] / (isPrecise ? 50 : 5);
 
     if(receiver->onMouseEvent) {
         receiver->onMouseEvent(event);
@@ -975,9 +977,6 @@ public:
         if(GetScrollbarPosition() == pos)
             return;
         [nsScroller setDoubleValue:(pos / (ssView.scrollerMax - ssView.scrollerMin))];
-        if(onScrollbarAdjusted) {
-            onScrollbarAdjusted(pos);
-        }
     }
 
     void Invalidate() override {

src/platform/guiwin.cpp

@@ -925,7 +925,7 @@ public:
                         event.y = pt.y / pixelRatio;
 
                         event.type = MouseEvent::Type::SCROLL_VERT;
-                        event.scrollDelta = GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? 1 : -1;
+                        event.scrollDelta = GET_WHEEL_DELTA_WPARAM(wParam) / WHEEL_DELTA;
                         break;
 
                     case WM_MOUSELEAVE:

src/textwin.cpp

@@ -252,8 +252,18 @@ void TextWindow::Init() {
                     MouseLeave();
                     return true;
                 } else if(event.type == MouseEvent::Type::SCROLL_VERT) {
-                    ScrollbarEvent(window->GetScrollbarPosition() -
-                                           LINE_HEIGHT / 2 * event.scrollDelta);
+                    if (event.scrollDelta == 0) {
+                        return true;
+                    }
+                    if (abs(event.scrollDelta) < 0.2) {
+                        if (event.scrollDelta > 0) {
+                            event.scrollDelta = 0.2;
+                        } else {
+                            event.scrollDelta = -0.2;
+                        }
+                    }
+                    double offset = LINE_HEIGHT / 2 * event.scrollDelta;
+                    ScrollbarEvent(window->GetScrollbarPosition() - offset);
                 }
                 return false;
             };
@@ -1148,7 +1158,6 @@ void TextWindow::ScrollbarEvent(double newPos) {
     int bottom = top[rows-1] + 2;
     newPos = min((int)newPos, bottom - halfRows);
     newPos = max((int)newPos, 0);
-
     if(newPos != scrollPos) {
         scrollPos = (int)newPos;
         window->SetScrollbarPosition(scrollPos);

src/ui.h

@@ -825,7 +825,7 @@ public:
     void MouseLeftDoubleClick(double x, double y);
     void MouseMiddleOrRightDown(double x, double y);
     void MouseRightUp(double x, double y);
-    void MouseScroll(double x, double y, int delta);
+    void MouseScroll(double x, double y, double delta);
     void MouseLeave();
     bool KeyboardEvent(Platform::KeyboardEvent event);
     void EditControlDone(const std::string &s);