From: Matt Keeter <matt.j.keeter@gmail.com>
Date: Mon, 24 Mar 2014 23:32:12 +0000 (-0400)
Subject: Zoom about mouse cursor
X-Git-Tag: v0.9.0~4^2~1
X-Git-Url: https://git.sur5r.net/?p=fstl;a=commitdiff_plain;h=54206d3f9caa44f91c51547cd1edbfc4091cc908

Zoom about mouse cursor
---

diff --git a/src/canvas.cpp b/src/canvas.cpp
index 1a1e060..15624da 100644
--- a/src/canvas.cpp
+++ b/src/canvas.cpp
@@ -161,7 +161,6 @@ void Canvas::mouseMoveEvent(QMouseEvent* event)
     }
     else if (event->buttons() & Qt::RightButton)
     {
-        qDebug() << d;
         center = transform_matrix().inverted() *
                  view_matrix().inverted() *
                  QVector3D(-d.x() / (0.5*width()),
@@ -173,6 +172,14 @@ void Canvas::mouseMoveEvent(QMouseEvent* event)
 
 void Canvas::wheelEvent(QWheelEvent *event)
 {
+    // Find GL position before the zoom operation
+    // (to zoom about mouse cursor)
+    auto p = event->pos();
+    QVector3D v(1 - p.x() / (0.5*width()),
+                p.y() / (0.5*height()) - 1, 0);
+    QVector3D a = transform_matrix().inverted() *
+                  view_matrix().inverted() * v;
+
     if (event->delta() < 0)
     {
         for (int i=0; i > event->delta(); --i)
@@ -183,5 +190,10 @@ void Canvas::wheelEvent(QWheelEvent *event)
         for (int i=0; i < event->delta(); ++i)
             zoom /= 1.001;
     }
+
+    // Then find the cursor's GL position post-zoom and adjust center.
+    QVector3D b = transform_matrix().inverted() *
+                  view_matrix().inverted() * v;
+    center += b - a;
     update();
 }