Writing the script code As explained in the previous section, the scripting functionality in Canvas is organized in a hierarchy that reflects the structure of Can- vas itself (see “Scripting hierarchy,” page 38.745). The Applica- tion object is at the top of the hierarchy. Scripts have to create a Canvas Application object in order to to access other parts of the hierarchy. In the Downsample script, you create the Canvas Application object when the script is started. First, define the global variable cvApp as Canvas.Application. In the proce- dure Form_Load, you then create a new Canvas Application object and assign it to cvApp. Dim cvApp As Canvas.Application ... Private Sub Form_Load() Set cvApp = New Canvas.Application End Sub Creating a Canvas Application object starts Canvas 8 in the background. In other words, the user interface will not be visible. Canvas is automatically shut down when the Application object reference in the script becomes invalid. In the Downsample script, the variable is globally accessible so it is valid until the script quits or Nothing is assigned to it. Next, you set cvApp to Nothing in the Form_Unload procedure, which is executed when a script quits. It is good practice to assign Nothing to Application object refer- ences. This ensures proper shutdown of the application when the ref- erences become obsolete. Private Sub Form_Unload(Cancel As Integer) Set cvApp = Nothing End Sub Most operations of the Downsample script happen in the SampleBtn_Click procedure, which is executed when the “Downsample” button is pressed. First, set the mouse pointer to look like an hourglass. This will signal to the user that the script is busy. At the end of the procedure when the downsampling process is fin- ished, the mouse pointer is reset to its default look. Screen.MousePointer = vbHourglass ...
Canvas 8 Help: Writing Scripts for Canvas (7 of 16)                                                 Page #749