IMSL C# Programmers Guide
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Actions >> Zoom |
Zoom
IMSL C# provides the functionality to implement a variety of zoom policies instead of implementing a single specific zoom policy. The following example shows how to build a zoom policy that draws a rubber-band box in a scatter plot and zooms both the x-axis and y-axis to correspond to the region selected. Zoom out is also implemented.
This code can be used as the basis of an implementation of other zoom policies. For example, with a function plot one might want to only change the x-axis in response to a zoom and leave the y-axis alone. In other situations it may be desirable to zoom in or out a fixed amount around the location of a mouse click.
Example
In the constructor:
MouseEventHandler
is added to the panel. A FrameChart
contains a
number of components, including a Panel
in which the chart is drawn. It is
important that the MouseEventHandler be added to the component in which
the chart is drawn, so that the MouseEventArgs
coordinates are the same
as the device coordinates of the chart.
A mouse press event starts the zoom. In response to the event a
MouseEventHandler
is added to the panel to listen for mouse drag events. The
location of this initial event is also recorded.
A mouse drag event resizes the area of the zoom. In response, the old rubber-band
box is erased and a new box is drawn. The new box has the initial mouse press location
as one corner and this drag event location as the opposite corner. The location
of this event is stored in (xLast
,yLast
).
A mouse release event completes the zoom. In response,
MouseEventHandler
with for MouseMove
is removed from the panel,
Window
attributes for the x-axis and y-axis are saved on a stack.
They may be used later to zoom out.
Window
is computed. The Window
is the range, in user coordinates,
along an axis. The method Axis.MapDeviceToUser
is used to map the
device (pixel) coordinates to the user coordinate space. The new windows are
constrained to be inside of the existing window.
Window
values will be used without
further modification.
The menu items, added by the constructor to the main menu, can be used to zoom
out. The added menu items add an EventHandler
with the menuItem_Click
delegate as the method called when these menu items are selected. The
menuItem_Click
method implements Out
by popping previous Window
at-
tribute values off a stack. It implements Restore
by re-enabling autoscaling.
(Download Code)
using System; using System.Windows.Forms; using System.Drawing; using Imsl.Chart2D; public class SampleZoom : FrameChart { private Panel panel; private AxisXY axis; private int xFirst, yFirst; private int xLast, yLast; private System.Collections.Stack stack; private MouseEventHandler mouseMoveHandler; public SampleZoom() { panel = this.Panel; Chart chart = this.Chart; axis = new AxisXY(chart); int n = 1000; double[] x = new double[n]; double[] y = new double[n]; Random ran = new Random(); for (int k = 0; k < n; k++) { x[k] = 10.0 * ran.NextDouble(); y[k] = 10.0 * ran.NextDouble(); } Data data = new Data(axis, x, y); data.DataType = Data.DATA_TYPE_MARKER; // add menu Zoom menu MenuItem menuZoom = new MenuItem(); menuZoom.Text = &Zoom; menuZoom.Shortcut = Shortcut.CtrlZ; AddMenuItem(menuZoom, Out, Shortcut.CtrlO); AddMenuItem(menuZoom, Restore, Shortcut.CtrlR); this.Menu.MenuItems.Add(menuZoom); // save x-axis and y-axis Window attributes on this stack. // they are used to zoom out one level. stack = new System.Collections.Stack(); // listen for mouse press events panel.MouseDown += new MouseEventHandler(Panel_MouseDown); panel.MouseUp += new MouseEventHandler(Panel_MouseUp); mouseMoveHandler = new MouseEventHandler(panel_MouseMove); } // Add a menu item private void AddMenuItem(MenuItem menuZoom, string title, Shortcut sc) { MenuItem menuItem = new MenuItem(title); menuItem.Text = title; menuItem.Shortcut = sc; menuZoom.MenuItems.Add(menuItem); menuItem.Click += new EventHandler(menuItem_Click); } // A mouse press starts the zoom // Record location of this point and listen for drag (motion) events. void Panel_MouseDown(object sender, MouseEventArgs e) { xFirst = xLast = e.X; yFirst = yLast = e.Y; panel.MouseMove += mouseMoveHandler; } // Releasing the mouse button ends the zoom // Stop listening for move events and update the Window attributes void Panel_MouseUp(object sender, MouseEventArgs e) { panel.MouseMove -= mouseMoveHandler; // ignore degenerate zooms if (xFirst == xLast || yFirst == yLast) { Refresh(); return; } // get window and convert to user coordinates double[] windowX = (double[])axis.AxisX.GetWindow(); double[] windowY = (double[])axis.AxisY.GetWindow(); // save the windows on the stack (for zoom out option) stack.Push(windowX); stack.Push(windowY); // get user coordinate of left-upper corner of the box // limit it to stay inside current window double[] boxLU = new double[2]; int x = Math.Min(xFirst, xLast); int y = Math.Min(yFirst, yLast); axis.MapDeviceToUser(x, y, boxLU); // get user coordinate of right-lower corner of the box // limit it to stay inside current window double[] boxRL = new double[2]; x = Math.Max(xFirst, xLast); y = Math.Max(yFirst, yLast); axis.MapDeviceToUser(x, y, boxRL); // set axis window to range of rubber-band box // and disable autoscale to force use of window settings axis.AutoscaleInput = ChartNode.AUTOSCALE_OFF; double xa = Math.Max(windowX[0], boxLU[0]); double xb = Math.Min(windowX[1], boxRL[0]); double ya = Math.Max(windowY[0], boxRL[1]); double yb = Math.Min(windowY[1], boxLU[1]); axis.AxisX.SetWindow(xa, xb); axis.AxisY.SetWindow(ya, yb); // force redraw of the chart Refresh(); } // Moving the mouse after a click continues the zoom. // Erase the old rubber band box and draw a new one // Also keep track of the location of this event void panel_MouseMove(object sender, MouseEventArgs e) { // erase previous rectangle Graphics g = panel.CreateGraphics(); DrawBox(g, Color.White); // draw new rectangle xLast = e.X; yLast = e.Y; DrawBox(g, Color.Red); } // Draw a box with (xFirst, yFirst) and (xLast, yLast) as its corners private void DrawBox(Graphics g, Color color) { int x = Math.Min(xFirst, xLast); int y = Math.Min(yFirst, yLast); int w = Math.Abs(xLast - xFirst); int h = Math.Abs(yLast - yFirst); g.DrawRectangle(new Pen(color), x, y, w, h); } void menuItem_Click(object sender, EventArgs e) { string cmd = ((MenuItem)sender).Text; if (cmd.Equals(Out)) { try { // zoom out by restoring window settings from the stack axis.AxisY.SetWindow((double[])stack.Pop()); axis.AxisX.SetWindow((double[])stack.Pop()); } catch (System.InvalidOperationException) { // no more levels to zoom out // restore original setting by turning on autoscale axis.AutoscaleInput = ChartNode.AUTOSCALE_DATA; } } else if (cmd.Equals(Restore)) { // restore original setting by turning on autoscale an empty stack axis.AutoscaleInput = ChartNode.AUTOSCALE_DATA; stack.Clear(); } // force redraw of the chart Refresh(); } public static void Main(string[] argv) { System.Windows.Forms.Application.Run(new SampleZoom()); } }
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