Best practices - Tips for creating content for mobile devices

To create Animate content for mobile devices, follow some basic principles. For example, Animate developers often avoid extremely complex artwork and excessive tweening or transparency.

Flash Lite developers face additional challenges because performance on mobile devices varies greatly. If content must be published to many different devices, developers sometimes have to author for the lowest common denominator.

Optimizing mobile content requires making trade‑offs. For example, one technique may make the content look better, while another results in better performance. As you evaluate these trade‑offs, you will be going back and forth repeatedly between testing in the emulator and testing on the target device. You must see your content on the actual device to evaluate the trueness of colors, text readability, physical interactions, UI responsiveness, and other aspects of the real mobile experience.

 The content about Flash Lite is not applicable for Flash CC and higher versions.

Flash Lite guidelines for animation in mobile devices

When creating animated content for a mobile devices, keep device CPU limitations in mind. Following these guidelines can help preventFlash Lite content from running slowly:

• When creating a new Flash Lite file, check that the document is set up correctly. Although Animate files scale smoothly, performance can suffer if the file is not running at its native Stage size and has to scale in the player. Try to set the document Stage size to match the resolution of the target device. Also set the Flash Player to the correct version of Flash Lite.

• Flash Lite can render vector graphics at low, medium, and high quality. The higher the rendering quality, the more smoothly and accurately Flash Lite renders vector graphics and the greater the demand on the device’s CPU. To provide complex animation, experiment with changing the player’s quality setting and then thoroughly test the SWF file. To control the rendering quality of a SWF file, use the _quality property or the SetQuality command. Valid values for the _quality property are LOW, MEDIUM, and HIGH.

• Limit the number of simultaneous tweens. Reduce the number of tweens, or sequence the animation so that one begins when another ends.

• Use transparency (alpha) effects on symbols sparingly because they are CPU intensive. In particular, avoid tweening symbols with alpha levels that are not fully opaque (less than 100%).

• Avoid CPU-intensive visual effects, such as large masks, extensive motion, alpha blending, extensive gradients, and complex vectors.

• Experiment with combinations of tweens, keyframe animations, and ActionScript-driven movement to produce the most efficient results.

• Rendering vector ovals and circles is much more memory intensive than rendering quadrangles. Using round and oval strokes also greatly increases CPU use.

• Test animations frequently on actual target devices.

• When Animate draws an animated region, it defines a rectangular bounding box around the area. Optimize the drawing by making that rectangle as small as possible. Avoid overlapping tweens, because Animate interprets the merged area as a single rectangle, resulting in a larger total region. Use Animate's Show Redraw Region feature to optimize the animation.

• Avoid using _alpha = 0 and _visible = false to hide on‑screen movie clips. If you simply turn a movie clip’s visibility off or change its alpha to zero, it is still included in line-rendering calculations, which can affect performance.

• Similarly, do not try to hide a movie clip by obscuring it behind another piece of artwork. It will still be included in the player’s calculations. Instead, move movie clips completely off the Stage or remove them by calling removeMovieClip.

Flash Lite bitmap and vector graphics in mobile devices

Flash Lite can render both vector and bitmap graphics. Each type of graphic has its advantages and disadvantages. The decision to use vector rather than bitmap graphics is not always clear and often depends on several factors.

Vector graphics are compactly represented in SWF files as mathematical equations and rendered at run time by the Flash Lite player. In contrast, bitmap graphics are represented as arrays of picture elements (pixels), which require more bytes of data. Therefore, using vector graphics in a file can help reduce file size and memory usage.

Vector graphics also maintain their smooth shapes when scaled in size. Bitmap images can appear boxy, or pixelated, when scaled.

Compared to bitmaps, vector graphics require more processing power to render, especially vector graphics that have many complex shapes and fills. Consequently, heavy use of vector shapes can sometimes reduce overall file performance. Because bitmap graphics do not require as much processing time to render as vector graphics, they are better choice for some files, for example, a complex road map meant to be animated and scrolled on a mobile phone.

Keep these considerations in mind:

• Avoid using outlines on vector shapes. Outlines have an inner and outer edge (fills have only one) and are twice the work to render.

• Corners are simpler to render than curves. When possible, use flat edges, especially with very small vector shapes.

• Optimization is especially helpful with small vector shapes such as icons. Complex icons may lose their details upon rendering, and the work of rendering the details is wasted.

• As a general rule, use bitmaps for small, complex images (such as icons) and vector graphics for larger and simpler ones.

• Import bitmap graphics at the correct size; don’t import large graphics and scale them down in Animate, because this wastes file size and run‑time memory.

• The Flash Lite player does not support bitmap smoothing. If a bitmap is scaled or rotated, it will have a chunky appearance. If it is necessary to scale or rotate a graphic, consider using a vector graphic instead.

• Text is essentially just a very complex vector shape. Of course, text is often critical, so it can rarely be avoided entirely. When text is needed, avoid animating it or placing it over an animation. Consider using text as a bitmap. For multiline dynamic and input text, the line break of the text string is not cached. Animate breaks lines at run time and recalculates the breaks every time the text field needs to be redrawn. Static text fields are not problematic, because the line breaking is precalculated at compile time. For dynamic content, using dynamic text fields is unavoidable, but when possible, consider using static text fields instead.

• Minimize the use of transparency in PNG files; Animate must calculate redraws even for the transparent portions of the bitmap. For example, with a transparent PNG file that represents a foreground element, don't export the transparent PNG at the full size of the screen. Instead, export it at the actual size of the foreground element.

• Try to group bitmap layers together and vector layers together. Animate needs to implement different renderers for bitmap and vector content, and switching between renderers takes time.

Set compression of Flash Lite bitmaps for mobile devices

When using bitmaps, you can set image-compression options (on a per-image basis or globally for all bitmap images) that reduce SWF file size.

Set compression options for an individual bitmap file

Set compression for all bitmap images

Optimizing Flash Lite frames for mobile devices

• Most devices that support Flash Liteplay back content at about 15 to 20 frames per second (fps). The frame rate can be as low as 6 fps. During development, set the document frame rate to approximate the playback speed of the target device. This shows how the content will run on a device with limited performance. Before publishing a final SWF file, set the document frame rate to at least 20 fps or higher to avoid limiting performance in case the device supports a higher frame rate.

• When using gotoAndPlay, remember that every frame between the current frame and the requested frame needs to be initialized before playing the requested frame. If many of these frames contain different content, it could be more efficient to use different movie clips rather than using the Timeline.

• Although preloading all content by putting it at the beginning of the file makes sense on the desktop, preloading on a mobile device can delay file startup. Space content throughout the file so that movie clips are initialized as they are used.

Optimizing ActionScript for Flash Lite content on mobile devices

Because of the processing speed and memory limitations on most mobile devices, follow these guidelines when developing ActionScript for Flash Lite content used on mobile devices:

• Keep the file and its code as simple as possible. Remove unused movie clips, delete unnecessary frame and code loops, and avoid too many frames or extraneous frames.

• Using FOR loops can be expensive because of the overhead incurred while the condition is checked with each iteration. When the costs of the iteration and the loop overhead are comparable, execute multiple operations individually instead of using a loop. The code may be longer, but performance will improve.

• Stop frame-based looping as soon as it is no longer needed.

• When possible, avoid string and array processing because it can be CPU-intensive.

• Always try to access properties directly rather than using ActionScript getter and setter methods, which have more overhead than other method calls.

• Manage events wisely. Keep event listener arrays compact by using conditions to check whether a listener exists (is not null) before calling it. Clear any active intervals by calling clearInterval, and remove any active listeners by calling removeListener before removing content using unloadapplication or removeapplicationClip. Animate does not re-collect SWF data memory (for example, from intervals and listeners) if any ActionScript functions are still referring to the SWF data when a movie clip is unloaded.

• When variables are no longer needed, delete them or set them to null, which marks them for garbage collection. Deleting variables helps optimize memory use during run time, because unneeded assets are removed from the SWF file. It is better to delete variables than to set them to null.

• Explicitly remove listeners from objects by calling removeListener before garbage collection.

• If a function is being called dynamically and passing a fixed set of parameters, use call instead of apply.

• Make namespaces (such as paths) more compact to reduce startup time. Every level in the package is compiled to an IF statement and causes a new Object call, so having fewer levels in the path saves time. For example, a path with the levels com.xxx.yyy.aaa.bbb.ccc.funtionName causes an object to be instantiated for com.xxx.yyy.aaa.bbb.ccc. Some Flash developers use preprocessor software to reduce the path to a unique identifier, such as 58923409876.functionName, before compiling the SWF code.

• If a file consists of multiple SWF files that use the same ActionScript classes, exclude those classes from select SWF files during compilation. This can help reduce file download time and run‑time memory requirements.

• Avoid using Object.watch and Object.unwatch, because every change to an object property requires the player to determine whether a change notification must be sent.

• If ActionScript code that executes on a keyframe in the timeline requires more than 1 second to complete, consider splitting up that code to execute over multiple keyframes.

• Remove trace statements from the code when publishing the SWF file. To do this, select the Omit Trace Actions check box on the Flash tab in the Publish Settings dialog box.

• Inheritance increases the number of method calls and uses more memory: a class that includes all the functionality it needs is more efficient at run time than a class that inherits some of its functionality from a superclass. Therefore, you may need to make a design trade‑off between extensibility of classes and efficiency of code.

• When one SWF file loads another SWF file that contains a custom ActionScript class (for example, foo.bar.CustomClass) and then unloads the SWF file, the class definition remains in memory. To save memory, explicitly delete any custom classes in unloaded SWF files. Use the delete statement and specify the fully qualified class name, such as: delete foo.bar.CustomClass.

• Limit the use of global variables, because they are not marked for garbage collection if the movie clip that defined them is removed.

• Avoid using the standard user interface components (available in the Components panel in Flash). These components are designed to run on desktop computers and are not optimized to run on mobile devices.

• Whenever possible, avoid deeply nested functions.

• Avoid referencing nonexistent variables, objects, or functions. Compared to the desktop version of Flash Player, Flash Lite 2 looks up references to nonexistent variables slowly, which can significantly affect performance.

• Avoid defining functions using anonymous syntax. For example, myObj.eventName = function{ ...}. Explicitly defined functions are more efficient, such as function myFunc { ...}; my Obj.eventName = myFunc;.

• Minimize the use of Math functions and floating-point numbers. Calculating these values slows performance. If you must use the Math routines, consider precalculating the values and storing them in an array of variables. Retrieving the values from a data table is much faster than having Flash calculate them at run time.

Managing Flash Lite file memory for mobile devices

Flash Lite regularly clears from memory any objects and variables that a file no longer references. This is known as garbage collection. Flash Lite runs its garbage-collection process once every 60 seconds, or whenever usage of file memory increases suddenly by 20% or more.

Although you cannot control how and when Flash Lite performs garbage collection, you can still free unneeded memory deliberately. For timeline or global variables, use the delete statement to free the memory that ActionScript objects use. For local variables—for example, a variable defined within a function definition—you can’t use the delete statement to free an object’s memory, but you can set to null the variable that references the object. This frees the memory that the object uses, provided there are no other references to that object.

The following two code examples show how to free memory that objects use by deleting the variable that references those objects. The examples are identical, except that the first example creates a timeline variable and the second creates a global variable.

As mentioned previously, you can’t use the delete statement to free memory that a local function variable uses. Instead, set the variable reference to null, which has the same effect as using delete.

Loading data for mobile devices in Flash Lite

When developing files for mobile devices, minimize the amount of data you attempt to load at one time. If you are loading external data into a Flash Lite file (for example, using XML.load), the device’s operating system may generate a “memory failure” error if insufficient memory is allocated for the incoming data. This situation can occur even if the total amount of remaining memory is sufficient.

For example, suppose a file attempts to load an XML file that’s 100 KB, but the device’s operating system has allocated only 30 KB to handle that incoming data stream. In this case, Flash Litedisplays an error message to the user, indicating that not enough memory is available.

To load large amounts of data, group the data in smaller pieces—for example, in several XML files—and make several data-loading calls for each piece. The size of each piece of data, and therefore the number of data-loading calls you need to make, varies by device and file. To determine an appropriate balance between the number of data requests and the likelihood of a memory failure, test files on a variety of target devices.

For optimum performance, avoid loading and parsing XML files if possible. Instead, store data in simple name/value pairs and load the data from a text file using loadVars or from precompiled SWF files.

Exclude classes from compilation for Flash Lite

To reduce the size of a SWF file, consider excluding classes from compilation but retaining the ability to access and use them for type checking. For example, try this if you are developing a file that uses multiple SWF files or shared libraries, especially those that access many of the same classes. Excluding classes helps avoid duplicating classes in those files.