Mobile Handling Stylus Input In WinCE Applications

Handling Stylus Input In WinCE Applications

While most CE devices have some sort of “keyboard”, these are often tiny

and awkward. For obvious reasons, users prefer the stylus. The

stylus-oriented interface is really a bonus for Windows CE programmers,

because it allows us to dispense with a great deal of the housekeeping that

goes with mouse and keyboard based user input on the desktop. Being a “touch

screen” kind of device, the stylus eliminates the need for floating cursors,

by inherently keeping track of insertion points, and the like.

When used to “tap” the CE device’s screen, the stylus is conceptually

treated as a “1 button mouse”. In general, you can assume existing programming

logic that detects left mouse button presses, including double clicks, will

port to CE with few or no changes. Code that handles right mouse button

presses will require some work-arounds, but porting this code is more a matter

of strategy than technique.

Porting Tip: Ease of use is the overriding consideration when designing

user input mechanisms.

On many CE devices, the keyboard is really a “last resort” for user input.

For this reason, you’ll want to give some consideration to allowing users to

provide input to your application using the “inking” capability of the CE

device. I use the word “consideration” advisedly, for there are some serious

issues to weigh in this matter. On the positive side, users really

like being able to treat their CE devices as “smart” memo pads.

Conversely, you’ll find that most of them really dislike “typing”

with a stylus or on a miniscule keyboard. This argues in favor of giving users

the opportunity to interact with your application in the ways they find most

convenient. On the other hand, the implementation of inking is maddeningly

asymmetrical across the various CE versions and platforms. If you choose to

aggressively support inking, expect to maintain a variety of code bases until

all of this gets sorted out.

With a view to the overarching theme of this book ( rapidly porting Win32

code to CE), I’ll offer my personal metric for deciding when to use inking in

the first CE version of your Win32 app:

  • Speed and ease of input are very important
  • Absolute accuracy is relatively unimportant
  • It’s not practical to supply a predetermined list of choices
  • The application doesn’t use the input to drive runtime decision

    making

Porting Tip: Use inking to store small to medium amounts of text that don’t

drive runtime decision making.

We’ll move on to explore example applications that show how to use the

stylus as a substitute for the mouse, and how to use it as a pen.

The Stylus Behaves As A One Button Mouse

The StylusTrack Example application shows how to receive and manipulate

stylus input. It captures the coordinates of the starting and ending points

of the line the user specifies by dragging the stylus across the screen, then

uses the point either as the diagonal of a rectangle or of the bounding

rectangle of an ellipse. Figure 1 shows how the StylusTrack example looks on

an HPC:

Figure 1 – The StylusTrack Application

The main source file for the StylusTrack example can be found in the

accompanying zipped code file. In the interest of brevity, we have omitted

the support files.

All of the drawing done in the StylusTrack example is done in response to

mouse messages. Notice that the message switch has no case for application

specific handling of the WM_PAINT message. Lets look at the initial stylus

handling, done in the WM_LBUTTONDOWN case of the message switch:

case WM_LBUTTONDOWN :
   //If Left button is down, save mouse coordinates in Line[0] point
   bLBDown = TRUE;
   line[0].x = LOWORD(lParam);
   line[0].y = HIWORD(lParam);
   break;

Notice that we don’t have to use SetCapture() to get the mouse movement

messages generated by the stylus. By default, CE sends the top window the

mouse messages. In response to the WM_LBUTTONDOWN we set the bLBDown to TRUE,

and copy the coordinates at which the mouse button went down from the lParam.

When the WM_LBUTTONUP message arrives, the drawing work begins. First, we

copy the point coordinates from the lParam of the message. We test them to

see if the stylus has actually moved, or if this was just a tap. If the stylus

moved we draw a line that is either the diagonal of the rectangle or the long

axis of the ellipse.

case WM_LBUTTONUP :
   //Draw last line. Since Left button down is false, 
   // no more lines are drawn
   //until next WM_LBUTTONDOWN message
   line[1].x = LOWORD(lParam);
   line[1].y = HIWORD(lParam);
   
if((line[0].x != line[1].x) || (line[0].y != line[1].y))
       { Polyline(hdc, line, 2);}
if ( bLBDown == TRUE )
    {
       hdc = GetDC(hWnd);
           Polyline(hdc, line, 2); 

Next, we use the coordinates to draw either the rectangle or the

ellipse:

if( iFigure == RECTANGLE )
{
    Rectangle( hdc, line[0].x, line[0].y, 
                    line[1].x, line[1].y );
}
if( iFigure == ELLIPSE )
{
    Ellipse( hdc, line[0].x, line[0].y, 
                    line[1].x, line[1].y );
}

Finally, we reinitialize the coordinates in the point array, release the

DC, and set bLBDown to FALSE.

      //reset value of initial point to end point
      line[1].x = 0;
      line[1].y = 0;
     line[0] = line[1];
   }

   ReleaseDC(hWnd, hdc);
}  //end if LButtonDown
bLBDown = FALSE;

If you wanted to continuously track the stylus, you could add a

WM_MOUSEMOVE case that accumulated points in a larger array, or simply did the

drawing as the stylus moved.

Downloads

Download source code: StylusInput.zip – 3

kb.

Looking Ahead:

In the next installment we’ll look at the how to use the CE ink

control.

About the Author

Nancy Nicolaisen is a software engineer who has designed

and implemented highly modular Windows CE products that include features such

as full remote diagnostics, CE-side data compression, dynamically constructed

user interface, automatic screen size detection, entry time data

validation.

In addition to writing for Developer.com, she has written several books

including Making Win 32 Applications Mobile.

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