diff --git a/openglcanvas.cpp b/openglcanvas.cpp
index 27a64627533860042295c9109bf476dc4fdbb5ac..ca83ae7b6eae0cf6219978483125f6d7325c5feb 100644
--- a/openglcanvas.cpp
+++ b/openglcanvas.cpp
@@ -446,7 +446,9 @@ int OpenGLCanvas::getTextureSize(const char * const progname, const char * textu
     pnm_readpaminit(in_file,&inpam,sizeof(struct pam));
 #endif
 
-    int size = inpam.width*inpam.height*inpam.depth*inpam.bytes_per_sample;
+    image_size_x=inpam.width;
+    image_size_y=inpam.height;
+    int size = image_size_x*image_size_y*inpam.depth*inpam.bytes_per_sample;
     pm_close(in_file);
 
     //fprintf(stderr,"size=%d\n",size);
@@ -590,6 +592,22 @@ void OpenGLCanvas::setShaders() {
 
 }
 
+void OpenGLCanvas::mousePressEvent(QMouseEvent *event){
+    lastPos=event->pos();
+    //fprintf(stderr,"mouse click\n");
+}
+
+void OpenGLCanvas::mouseMoveEvent(QMouseEvent *event){
+    // scroll with the left button
+    if(event->buttons()==Qt::LeftButton){
+        // compute the delta and move the image
+        center_lambda+=(event->x()-lastPos.x())*3.1415926f/image_size_x;
+        center_phi+=(event->y()-lastPos.y())*3.1415926f/image_size_y;
+        lastPos=event->pos();
+        updateGL();
+    }
+}
+
 void OpenGLCanvas::paintGL(){
 
     float fov_rads = (fov/180.f)*1.5708f;
diff --git a/openglcanvas.h b/openglcanvas.h
index 88dced1c7929508ed8db2306af347a1745324ffa..364ce83d80f5a5182f0ff4b607be84d26a5c8b3c 100644
--- a/openglcanvas.h
+++ b/openglcanvas.h
@@ -55,6 +55,8 @@ protected:
     void readTextureBytes(const char * const progname, const char * texturePath,unsigned char * textureBytes,int * outImageWidth, int * outImageHeight);
     char *textFileRead(char *fn);
     void setShaders();
+    void mousePressEvent(QMouseEvent *event);
+    void mouseMoveEvent(QMouseEvent *event);
 
 signals:
     void fps(QString newFPS);
@@ -93,6 +95,12 @@ private:
     // options set in the rc file
     char* shader_dir;
     char* input_image_file;
+
+    // input image size (determined automatically)
+    int image_size_x;
+    int image_size_y;
+
+    QPoint lastPos; // mouse click position
 };
 
 #endif // OPENGLCANVAS_H