GIS二次开发之缩小

     前一篇随笔中记录了地图放大功能的实现，其中很多方法和这篇中要说的缩小很像，比如ControlsMapZoomOutTool和ControlsMapZoomOutFixedCommand。那在这篇中就忽略掉这两个方法的实现了，直接看看自定义缩小功能的实现代码

        public MapZoomOut()
        {
            string[] res = GetType().Assembly.GetManifestResourceNames();

            base.m_bitmap = new System.Drawing.Bitmap(GetType().Assembly.GetManifestResourceStream("Commands.zoomout.bmp"));
            base.m_caption = "缩小地图";
            base.m_category = "ToolBar";
            base.m_message = "缩小地图";
            base.m_name = "ToolBar_MapPan";
            base.m_toolTip = "缩小";
            m_ZoomOutStart = true;
            m_feedBack = null;
            try
            {
                base.m_cursor = new System.Windows.Forms.Cursor(GetType().Assembly.GetManifestResourceStream("Commands.ZoomOut.CUR"));
            }
            catch (Exception ex)
            {

            }
        }

        public override void OnCreate(object hook)
        {
            m_HookHelper.Hook = hook;
            try
            {
                m_pActiveView = m_HookHelper.ActiveView;
            }
            catch { }
        }

        public override void OnMouseDown(int Button, int Shift, int X, int Y)
        {
            if (null == m_pActiveView) return;
            m_pPoint = m_pActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y);
            m_ZoomOutStart = true;
            m_feedBack = null;
        }

        public override void OnMouseMove(int Button, int Shift, int X, int Y)
        {
            if (null == m_pActiveView) return;
            if (!m_ZoomOutStart) return;

            if (m_feedBack == null)
            {
                m_feedBack = new NewEnvelopeFeedbackClass();
                if (Button == 1)
                {
                    m_feedBack.Display = m_pActiveView.ScreenDisplay;
                    m_feedBack.Start(m_pPoint);
                }
            }
            m_feedBack.MoveTo(m_pActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y));
        }

        public override void OnMouseUp(int Button, int Shift, int X, int Y)
        {
            if (null == m_pActiveView) return;
            if (!m_ZoomOutStart) return;
            IEnvelope m_pEnvelope = new EnvelopeClass();
            if (null == m_feedBack) //点击缩小
            {
                m_pEnvelope = m_pActiveView.Extent;
                m_pEnvelope.Expand(2, 2, true);
                m_pActiveView.Extent.CenterAt(m_pPoint);
            }
            else //拉框缩小
            {
                IEnvelope m_pFeedEnvelope = new EnvelopeClass();
                m_pFeedEnvelope = m_feedBack.Stop();
                try
                {
                    //这里是与放大代码不同的地方
                    double newWidth = m_pActiveView.Extent.Width * (m_pActiveView.Extent.Width / m_pFeedEnvelope.Width);
                    double newHeight = m_pActiveView.Extent.Height * (m_pActiveView.Extent.Height / m_pFeedEnvelope.Height);

                    double newXmin = m_pActiveView.Extent.XMin - ((m_pFeedEnvelope.XMin - m_pActiveView.Extent.XMin) * (m_pActiveView.Extent.Width / m_pFeedEnvelope.Width));
                    double newYmin = m_pActiveView.Extent.YMin - ((m_pFeedEnvelope.YMin - m_pActiveView.Extent.YMin) * (m_pActiveView.Extent.Height / m_pFeedEnvelope.Height));

                    m_pEnvelope.PutCoords(newXmin, newYmin, newXmin + newWidth, newYmin + newHeight);
                }
                catch
                {
                    m_pEnvelope = m_pActiveView.Extent;
                    m_pEnvelope.Expand(2, 2, true);
                    m_pActiveView.Extent.CenterAt(m_pPoint);
                    m_feedBack = null;
                    m_ZoomOutStart = false;
                }
            }

            m_pActiveView.Extent = m_pEnvelope;

            m_pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGeography, null, null);

            m_feedBack = null;
            Marshal.ReleaseComObject(m_feedBack);
            m_ZoomOutStart = false;
        }

        public override void OnKeyDown(int keyCode, int Shift)
        {
            if (keyCode == 27)
            {
                m_ZoomOutStart = false;
                base.m_cursor = System.Windows.Forms.Cursors.Default;
            }
        }

       可以看到缩小与放大不同之处

       ①：在点击缩放的时候m_pEnvelope.Expand(0.5,0.5,true) 和m_pEnvelope.Expand(2,2,true)的不同，应该很容易理解，打个比方，比如把当前的地图比作为1m*1m的标准地图，Expand(0.5,0.5,true),相当于是说将0.5m*0.5m的地图视图放大1m*1m的“地图框架”中，为了充满这个“地图框架”，应该要放大。（哈哈，应该可以这样理解），同样，缩小也就好理解了。

       ②：在拉框缩放的时候，放大中直接按照绘制的矩形框的大小进行放大，在缩小的时候，需要set new coordinate，就像屏幕的分辨率一样，重置到当前“屏幕”的大小（就是重定义ActiveView.Extent的Xmin，Ymin，Xmax，Ymax）。