From 9e150f2bfbb1759988b3b0216c0b4d6c310d1ce1 Mon Sep 17 00:00:00 2001
From: Sven Eberhardt <sven2@goldwipf.de>
Date: Sat, 8 Oct 2016 19:04:09 -0400
Subject: [PATCH] Viewport zoom towards center and fix scrolling

---
 src/editor/C4ConsoleQtViewport.cpp | 13 ++++++++++---
 src/editor/C4ConsoleQtViewport.h   |  1 +
 src/game/C4Viewport.cpp            | 19 +++++++++++++++----
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/src/editor/C4ConsoleQtViewport.cpp b/src/editor/C4ConsoleQtViewport.cpp
index 0ad868375..e7beccf3b 100644
--- a/src/editor/C4ConsoleQtViewport.cpp
+++ b/src/editor/C4ConsoleQtViewport.cpp
@@ -279,6 +279,8 @@ void C4ConsoleQtViewportView::wheelEvent(QWheelEvent *event)
 			cvp->ScrollView(x, y);
 		}
 	}
+	// Event has been handled - do not forward to scroll bars
+	event->accept();
 }
 
 void C4ConsoleQtViewportView::focusInEvent(QFocusEvent * event)
@@ -422,7 +424,7 @@ void C4ConsoleQtViewportView::paintGL()
 
 
 C4ConsoleQtViewportScrollArea::C4ConsoleQtViewportScrollArea(class C4ConsoleQtViewportDockWidget *dock)
-	: QAbstractScrollArea(dock), dock(dock), cvp(dock->cvp->cvp)
+	: QAbstractScrollArea(dock), dock(dock), cvp(dock->cvp->cvp), is_updating_scrollbars(0)
 {
 	cvp->scrollarea = this;
 	// No scroll bars by default. Neutral viewports will toggle this.
@@ -432,8 +434,11 @@ C4ConsoleQtViewportScrollArea::C4ConsoleQtViewportScrollArea(class C4ConsoleQtVi
 void C4ConsoleQtViewportScrollArea::scrollContentsBy(int dx, int dy)
 {
 	// Just use the absolute position in any case.
-	cvp->SetViewX(horizontalScrollBar()->value());
-	cvp->SetViewY(verticalScrollBar()->value());
+	if (!is_updating_scrollbars)
+	{
+		cvp->SetViewX(horizontalScrollBar()->value());
+		cvp->SetViewY(verticalScrollBar()->value());
+	}
 }
 
 bool C4ConsoleQtViewportScrollArea::viewportEvent(QEvent *e)
@@ -451,6 +456,7 @@ void C4ConsoleQtViewportScrollArea::setupViewport(QWidget *viewport)
 
 void C4ConsoleQtViewportScrollArea::ScrollBarsByViewPosition()
 {
+	++is_updating_scrollbars; // Do not shift view just from updating scroll bars
 	int x = viewport()->width() / cvp->GetZoom();
 	horizontalScrollBar()->setRange(0, ::Landscape.GetWidth() - x);
 	horizontalScrollBar()->setPageStep(x);
@@ -460,6 +466,7 @@ void C4ConsoleQtViewportScrollArea::ScrollBarsByViewPosition()
 	verticalScrollBar()->setRange(0, ::Landscape.GetHeight() - y);
 	verticalScrollBar()->setPageStep(y);
 	verticalScrollBar()->setValue(cvp->GetViewY());
+	--is_updating_scrollbars;
 }
 
 void C4ConsoleQtViewportScrollArea::setScrollBarVisibility(bool visible)
diff --git a/src/editor/C4ConsoleQtViewport.h b/src/editor/C4ConsoleQtViewport.h
index b7d0f0b7a..c0cb4df94 100644
--- a/src/editor/C4ConsoleQtViewport.h
+++ b/src/editor/C4ConsoleQtViewport.h
@@ -65,6 +65,7 @@ class C4ConsoleQtViewportScrollArea : public QAbstractScrollArea
 	
 	class C4ConsoleQtViewportDockWidget *dock;
 	class C4Viewport *cvp;
+	int32_t is_updating_scrollbars;
 
 protected:
 	void scrollContentsBy(int dx, int dy) override;
diff --git a/src/game/C4Viewport.cpp b/src/game/C4Viewport.cpp
index 548798ae7..67bd83f7d 100644
--- a/src/game/C4Viewport.cpp
+++ b/src/game/C4Viewport.cpp
@@ -516,10 +516,21 @@ void C4Viewport::AdjustZoomAndPosition()
 
 		if (Zoom == 0)
 			Zoom = ZoomTarget;
-		if (Zoom < ZoomTarget)
-			Zoom = std::min(Zoom * ZoomAdjustFactor, ZoomTarget);
-		if (Zoom > ZoomTarget)
-			Zoom = std::max(Zoom / ZoomAdjustFactor, ZoomTarget);
+		else
+		{
+			// Remember old viewport center
+			float view_mid_x = this->viewX + float(this->ViewWdt) / Zoom / 2.0f;
+			float view_mid_y = this->viewY + float(this->ViewHgt) / Zoom / 2.0f;
+
+			if (Zoom < ZoomTarget)
+				Zoom = std::min(Zoom * ZoomAdjustFactor, ZoomTarget);
+			if (Zoom > ZoomTarget)
+				Zoom = std::max(Zoom / ZoomAdjustFactor, ZoomTarget);
+
+			// Restore new viewport center
+			this->viewX = view_mid_x - float(this->ViewWdt) / Zoom / 2.0f;
+			this->viewY = view_mid_y - float(this->ViewHgt) / Zoom / 2.0f;
+		}
 	}
 	// Adjust position
 	AdjustPosition(false);