How do I create and move graphics in an app?

There are many cases where you might want to create an app that allows the user to author content.

  • Flowchart app
  • Image annotation app
  • Wireframing app

You can allow users to create and edit LiveCode controls within an app. In this lesson we will see how to create a very simple example of this type of app which you could use as a basis for a more complex app.

The User Interface

The app consists of a single card containing

  • group "templates"
    • graphic "Hexagon"
    • graphic "Circle"
    • graphic "Sqaure"
  • button "Clear Canvas"
  • group "Canvas"
  • 2 line graphics

Creating graphics

The first step is to allow the user to add graphics to the canvas. Clicking on one of the template shapes will add the shape to the canvas.

Because the template graphics are grouped together we can add the code to the group script. Select the "templates" group, open the Script Editor and add this mouseUp handler.

on mouseUp
   createShape the short name of the target
end mouseUp

We use the target to check which template was actually clicked. This saves us from adding code in multiple places.

The createShape command is implemented on the Card Script, open the Card Script and add the command.

command createShape pShape
   copy graphic pShape of group "Templates" to group "Canvas"
   set the loc of it to the loc of group "Canvas"
end createShape
  • Make a copy of the template graphic in the "Canvas" group
  • Place the new graphic at the center of the canvas

Switch to Run mode and try it.

Dragging graphics around the canvas

The next step is to allow the user to move the graphics they have created around the canvas. Again, becuase we have created the new graphics in the "Canvas" group we can add the code to the group script.

Open the Script Editor for the group and add the mouseDown handler.

on mouseDown
   grab the target
end mouseDown

The grab command causes an object to follow the movements of the mouse.

Switch to Run mode and try it.

Adding text to graphics

The next feature allows the user to set the text that is displayed on a graphic. Again we will add the code to the "canvas" group script, for this feature we will handle the mouseDoubleUp message

on mouseDoubleUp
   local tTarget
   put the name of the target into tTarget
   
   ask "Please enter the text to be displayed"
   if the result is not "Cancel" then
      set the name of tTarget to it
   end if
end mouseDoubleUp
  • Get the identifier of the graphic that was double clicked
  • Allow the user to enter the text they want to display
  • Set the name property of the graphic to the text entered by the user

Clearing the canvas

Finally we will add code to the "Clear Canvas" button to reset the canvas by deleting all the graphics that have been added.

Add a mouseUp handler to the "Clear Canvas" button

on mouseUp
   clearCanvas
end mouseUp

And add the clearCanvas command to the Card Script

command clearCanvas
   repeat with x = the number of graphics of group "Canvas" down to 1
      delete graphic x of group "Canvas"
   end repeat
end clearCanvas

Note that we repeat down through the graphics. Because we are referring to the graphics by number as we delete them the number of graphics changes, by counting down the graphic we are deleting will always exists.

Possible additional features

There are many ways you could expand this example to create a more fully featured application

  • Automatically resize graphics or text to show all text
  • Add color editiors
  • Add lines between graphics
  • Print the canvas

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