In: Categories » Computers and technology » Flash » Using Mathematical Operators in ActionScript
|
You want to modify something over time, such as the rotation or position of a movie clip. Use the compound assignment operators to change a variable or property in increments. Or, if incrementing or decrementing by one, use the prefix or postfix increment or decrement operators. Often, you'll want the new value of a variable or property to depend on the previous value. For example, you might want to move a movie clip to a new position that is 10 pixels to the right of its current position. In an assignment statement—any statement using the assignment operator (an equals sign)—the expression to the right of the equals sign is evaluated and the result is stored in the variable or property on the left side. Therefore, you can modify the value of a variable in an expression on the right side of the equation and assign that new value to the very same variable on the left side of the equation. Although the following may look strange to those who remember basic algebra, it is very common for a variable to be set equal to itself plus a number: // Add 6 to the current value of myNum and assign that new value back to myNum. For // example, if myNum was 3, this statement sets it to 9. myNum = myNum + 6; However, when performing mathematical operations, it is often more convenient to use one of the compound assignment operators, which combine a mathematical operator with the assignment operator. The +=, -=, *=, and /= operators are the most prevalent compound assignment operators. When you use one of these compound assignment operators, the value on the right side of the assignment operator is added to, subtracted from, multiplied by, or divided into the value of the variable on the left, and the new value is assigned to the same variable. The following are a few examples of equivalent statements. These statements both add 6 to the existing value of myNum: myNum = myNum + 6; myNum += 6; These statements both subtract 6 from the existing value of myNum: myNum = myNum - 6; myNum -= 6; These statements both multiply myNum by anotherNum: myNum = myNum * anotherNum; myNum *= anotherNum; These statements both divide myNum by anotherNum: myNum = myNum / anotherNum; myNum /= anotherNum; There should be no space between the two symbols that make up a compound assignment operator. Additionally, if you are incrementing or decrementing a variable by 1, you can use the increment or decrement operators (-- and ++). This statement adds 1 to myNum: myNum++; and has the same effect as either of these statements: myNum = myNum + 1; myNum += 1; This statement subtracts 1 from myNum: myNum--; and has the same effect as either of these statements: myNum = myNum - 1; myNum -= 1; You can use the increment and decrement operators before or after the variable or property on which they operate . If used before the operand, they are called prefix operators. If used after the operand, they are called postfix operators. The prefix and postfix operators modify the operand in the same way but at different times. In some circumstances, there is no net difference in their operation, but the distinction is still important in many cases. When using prefix operators, the value is modified before the remainder of the statement or expression is evaluated. And if using postfix operators, the value is modified after the remainder of the statement has executed. Note how the first example increments myNum after displaying its value, whereas the second example increments myNum before displaying its value: myNum = 5; trace(myNum++); // Displays: 5 trace(myNum); // Displays: 6 myNum = 5; trace(++myNum); // Displays: 6 trace(myNum); // Displays: 6 Getting back to our original problem, you can use mathematical operators to modify a property over time. This example causes the specified movie clip to rotate by 5 degrees for each tick of the frame rate: myClip_mc.onEnterFrame = function ( ) {
this._rotation += 5;
};
|
legal disclaimer
1) Our website is not responsible for the information contained by this article as well for any and all copyright infringements by authors and writers. E-articles is a free information resource. If you suspect this article for any copyright infringements, please read the Terms of service and contact us to investigate the problem.
2) The E-articles directory team is not responsible for inaccuracies, falsehoods, or any other types of misinformation this tutorial may contain and will not be liable for any loss or damage suffered by a user through the user's reliance on the information gained here. Please read the Terms of service
Useful tools and features
If you like this article (tutorial), please link to it from your web page using the information above. Linking to this page, this is the only way to help us improve our service, the same time providing your visitors with a way to improve their online experience.
related articles
Use the Drawing API to create a shape and then use MovicClip.setMask( ) to apply the mask. Masks can be used to create unique shapes or visual effects. For example, you can use masks to create wipes and transitions or interesting animations in which only the masked portion of the artwork is visible at a given time. You can even create masks that change shape over time, and use them to mask bitmapped graphics (in movie clips). You can use any movie clip as a mask of another movie clip using the setMask( ) method. The setMask( ...
2. Drawing a Triangle using ActionScript
Create a custom MovieClip.drawTriangle( ) method using the Drawing API and invoke it on a movie clip. You can determine and plot the vertices of a triangle given the lengths of two sides and the angle between them. This is a better approach than specifying the lengths of the three sides because knowing the lengths of two sides and the angle between them always determines a triangle, whereas three arbitrary sides may not fit together to make a triangle. The custom drawTriangle( ) method accepts six parameters: ab ...
3. ActionScript: Filling a Shape with a Solid or Translucent Color
Use the beginFill( ) and endFill( ) methods to initiate and close a shape drawn at runtime. To draw a filled shape, call beginFill( ) prior to any other drawing methods, including the custom methods you have defined such as drawCircle( ) and drawPolygon( ). Invoke endFill( ) after calling other drawing methods to create the shape. You cannot apply a fill to an existing shape drawn at authoring time or runtime. You must invoke beginFill( ) before drawing the shape to be filled. This example creates a solid blue ...
4. Drawing a rectangle using ActionScript
Create a custom MovieClip.drawSimpleRectangle( ) method using the Drawing API and invoke it on a movie clip. To draw a simple rectangle, specify the stroke's attributes using the lineStyle( ) method and then draw four lines using the lineTo( ) method: // Create rectangle_mc with a depth of 1 on the main timeline. _root.createEmptyMovieClip("rectangle_mc", 1); // Specify a one-pixel, solid, black line. rectangle_mc.lineStyle(1, 0x000000, 100); // Draw four lines to form the perimeter ...
You want to draw a rectangle with rounded corners, an offset, or rotation.Create a custom MovieClip.drawRectangle( ) method using the Drawing API and invoke it on a movie clip. The drawSimpleRectangle( ) method is, as the name suggests, quite simple. Let's create a more complex version that also: Draws a rectangle with a specified angle of rotation Let's you specify the rectangle center's coordinates Can draw a rectangle with rounded corners The drawRectangle( ) method accepts...
6. Reusing and Organizing Code in Flash Movies
You want to reuse code that you've created for one project in another Flash movie. Or you want to write your ActionScript code in an external text editor. Place your ActionScript code in external .as files and use the #include directive to add them to your Flash movies: // Adds all the code within MyActionScriptFile.as to your Flash movie. #include "MyActionScriptFile.as" Use the #include directive to incorporate code from external text files into your Flash movie during compilation from a .fla file ...
7. Drawing a Circle using ActionScript
Create a custom MovieClip.drawCircle( ) method using the Drawing API and invoke it on a movie clip. You can create a circle in ActionScript with eight curves. Fewer curves results in a distorted circle and too many curves hinders performance. Let's create a custom method of the MovieClip class for drawing circles. This method, drawCircle( ), allows for three parameters: radius The radius of the circle x The x coordinate of the circle's center point. If undefined, the circle is centered at x =...
8. ActionScript: Repeating a Task at Timed Intervals
You want to perform an action or actions at a specific timed interval. Use the setInterval( ) function. The setInterval( ) function allows you to specify an interval (in milliseconds) at which your Flash movie will invoke a function. Use setInterval( ) to perform a particular action over time but not necessarily at the frequency of the frame rate of the movie. // Define a function. function myIntervalFunction ( ) { // Output the difference between the current timer value and its value from the ...
9. Mouse Location Flash Script
Not only can you get the location of a movie clip on the screen, you can even get the location of the mouse, also known as the cursor. What is the difference between the mouse and the cursor? The mouse is the physical device attached to your computer. You may even have a track pad or tablet instead. The cursor is the graphic that moves around the screen as you move your mouse. So, technically, cursor is the term I should be using here. However, ActionScript uses the term mouse in its keywords. I will therefore use mouse and cursor i...