.NET/Java PDF, Tiff, Barcode SDK Library

private void Rotate(double duration) { // This is the total circumference of turning circle double circum = Math.PI * PlatformWidth; // This is the total distance traveled double d = duration * MotorSpeed; if (LeftMotorState == MotorState.Reversed) { // And we're going backwards if the motors are reversed d *= -1.0; } // So we've driven it this proportion of the way round double proportionOfWholeCircle = d / circum; // Once round is 360 degrees (or 2pi radians), so we have traveled // this far: CurrentOrientation = CurrentOrientation + (Math.PI * 2.0 * proportionOfWholeCircle); } private void Drive(double duration) { // This is the total distance traveled double d = duration * MotorSpeed; if (LeftMotorState == MotorState.Reversed) { // And we're going backwards if the motors are reversed d *= -1.0;

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} // Bit of trigonometry for the change in the x,y coordinates double deltaX = d * Math.Sin(CurrentOrientation); double deltaY = d * Math.Cos(CurrentOrientation); // And update the position CurrentPosition = new Point(CurrentPosition.X + deltaX, CurrentPosition.Y + deltaY);

}

The simple API for XML (SAX) can be used only to read XML files. It works by reading the file and locating opening tags, closing tags, attributes, and text; and calling functions in the handler objects set up to handle the different parts of an XML document. The benefit of this approach compared with using a DOM document is that the entire file does not have to be loaded into memory at once. To use SAX, three classes are used: QXmlInputSource, QXmlSimpleReader, and a handler. Listing 8-16 shows the main function of an application using SAX to parse a file. The QXmlInputSource is used to provide a predefined interface between the QFile and the QXmlSimpleReader object. The QXmlSimpleReader is a specialized version of the QXmlReader class. The simple reader is powerful enough to be used in almost all cases. The reader has a content handler that is assigned using the setContentHandler method. The content handler must inherit the QXmlContentHandler, and that is exactly what the MyHandler class does. Having set everything up, it is just a matter of calling the parse(const QXmlInputSource *, bool) method, passing the XML input source object as a parameter, and waiting for the reader to report everything worth knowing to the handler. Listing 8-16. Setting up a SAX reader with a custom handler class int main( int argc, char **argv ) { QFile file( "simple.xml" ); if( !file.open( QIODevice::ReadOnly | QIODevice::Text ) ) { qDebug( "Failed to open file for reading." ); return -1; } QXmlInputSource source( &file ); MyHandler handler;

Let s write a quick test program to see whether the code we ve written actually does what we expect (see Example 6-4).

asynchronous functionality is extremely unobtrusive. You don t intercept or override the existing click functionality (or any other functionality, for that matter) and just enhance it by providing the additional tags used for the update functionality. ToDoList is an excellent example of a small ASP .NET application and how it can be enhanced with Ajax functionality using Atlas. The server control set you saw in 6 has been carefully designed and implemented to allow you to enhance existing applications as easily as possible and in a manner that involves touching your existing code as little as possible. Additionally, for new applications, it involves reusing your existing skills in ASP .NET and lowers the learning curve drastically. In the next example, you will look at the official reference application for Atlas the Atlas wiki.

static void Main(string[] args) { // Here's our turtle Turtle arthurTheTurtle = new Turtle {PlatformWidth = 10.0, PlatformHeight = 10.0, MotorSpeed = 5.0}; ShowPosition(arthurTheTurtle); // We want to proceed forwards arthurTheTurtle.LeftMotorState = MotorState.Running; arthurTheTurtle.RightMotorState = MotorState.Running; // For two seconds arthurTheTurtle.RunFor(2.0); ShowPosition(arthurTheTurtle); // Now, let's rotate clockwise for a bit arthurTheTurtle.RightMotorState = MotorState.Reversed; // PI / 2 seconds should do the trick arthurTheTurtle.RunFor(Math.PI / 2.0); ShowPosition(arthurTheTurtle); // And let's go into reverse arthurTheTurtle.RightMotorState = MotorState.Reversed; arthurTheTurtle.LeftMotorState = MotorState.Reversed; // And run for 5 seconds arthurTheTurtle.RunFor(5); ShowPosition(arthurTheTurtle); // Then rotate back the other way arthurTheTurtle.RightMotorState = MotorState.Running; // And run for PI/4 seconds to give us 45 degrees arthurTheTurtle.RunFor(Math.PI / 4.0); ShowPosition(arthurTheTurtle);

// And finally drive backwards for a bit arthurTheTurtle.RightMotorState = MotorState.Reversed; arthurTheTurtle.LeftMotorState = MotorState.Reversed; arthurTheTurtle.RunFor(Math.Cos(Math.PI / 4.0)); ShowPosition(arthurTheTurtle); Console.ReadKey(); } private static void ShowPosition(Turtle arthurTheTurtle) { Console.WriteLine( "Arthur is at ({0}) and is pointing at angle {1:0.00} radians.", arthurTheTurtle.CurrentPosition, arthurTheTurtle.CurrentOrientation); }

We chose the times for which to run quite carefully so that we end up going through relatively readable distances and angles. (Hey, someone could design a more usable facade over this API!) If we compile and run, we see the following output: