Designing an Avatar in Flash Multiplayer Virtual Worlds

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Designing an avatar

Avatar is very important in a virtual world because most of the features are designed around avatars. Users interact with each other via their avatars, they explore the virtual world via avatars, and they complete challenges to level up their avatars.

An avatar is composited by graphics and animation.

The avatar graphics are its looks. It is not a static image but a collection of images to display the directions and appearance. There are different approaches of drawing the avatar graphics depending on the render methods and how many directions and animations the avatar needs.

Animations represent different actions of the avatar. The most basic animation is walking. Other animations such as hand waving and throwing objects are also common. There will be different animation sets for different virtual world designs. A fighting topic virtual world will probably contain a collection of fighting animation sets. A hunting topic virtual world will contain animations of collection items and using hunting tools.

Determining the direction numbers of avatars’ views

Isometric tile is composed by diamond shapes with four-edge connection to the other tiles. It is not hard to imagine that every avatar in the isometric view may face towards four directions. They are the north east, south east, south west, and north west.

However, sometimes using only these four directions may not be enough; some game designs may require the avatar to face the user or walk to the other isometric tile a cross the diamond corner. In this case, eight directions are required.

The direction number of the avatars affects the artwork drawing directly. Just imagine that we are building a virtual world where players can fight with each other. How many animations are there for an avatar to fight? Say, five sets of animations. How many directions can the avatar faces? 4? 8? Or even 12? For example, we are now talking about five sets of animations with 8 directions of each avatar. That’s already 40 animations for only one avatar. We may design the virtual world to have 12 kinds of avatars and each avatar to have different clothes for customization. The graphics workload keeps increasing when only one of these aspects increases.

That’s why I often consider different approaches that reduce the graphic workload of the avatars. Take four directions as an example. In most cases, we have very similar animations when the avatar is facing south-east and south-west. And the animation of north-east and north-west are similar too. Therefore, it is a common technique that mirrors the animation of west side into east side. It can be easily done in Flash by just changing the x-axis of the scaling property to between -1 and 1. This property results in the avatar flipping from one side to another side. For a 4-directions animation set, only 2 directions need to be drawn. In an 8-directions animation set, only 5 directions need to be drawn.

Next, we will discuss the rendering methods that will conclude how the amount of directions, animations, and customization affect the graphic workload.

Rendering avatars in Flash virtual world

There are different approaches to render avatars in Flash virtual world. Each rendered method comes with both advantages and disadvantages. Some methods take more time to draw with fancy outlook while others may take more time to program.

It is important to decide which rendering methods of the avatar are required in predevelopment stage. It will be much more difficult to change the rendering method after the project is in development.

We will discuss different rendering methods and the pros and cons of them.

Drawing an avatar using vector animation

It is convenient to use the Flash native vector drawing for avatar because every drawing can be done within the Flash. The output can be cute and cartoon style.

One advantage of using vector is that color customization is easy to implement by using the native ActionScript color transform. We can easily assign different colors to different parts of the avatar without extra graphic drawing.

Another advantage of using vector animation is that we can scale up and down the avatars whenever needed. It is useful when we need to zoom in or out of the map and the avatars in the virtual world. The following graph shows the comparison of scaling up a vector and bitmap graphic:

The disadvantage is that we need to draw the animation of every part of the avatar in every direction frame by frame. Flash tweening can help but the workload is heavier than other methods. We can prerender the animations or control them by ActionScript in methods discussed later. In vector animation, every animation is hand-drawn and thus any late modification on the avatar design can cost quite a lot of workload. There may not be too many directions of the avatars meaning the rotation of the avatars will not be very smooth.

Rendering avatars using bitmap sprite sheet

Sprite sheet is a graphics technique that is used in almost all game platforms. Sprite sheet is a large bitmap file that contains every frame of animation. Bitmap data from each frame is masked and rendered to the screen. A Flash developer may think that there is a timeline with frame one on the top left and counting the frame from left to right in each row from top to bottom.

This technique is useful when the avatar graphic designer has experience in other game platforms. Another advantage of using bitmap data is faster rendering than vector in Flash player.

The other advantage is the sprite sheet can be rendered from 3D software. For example, we can make an avatar model in Maya (http://autodesk.com/maya) or 3Ds Max (http://autodesk.com/3dsmax) with animations set up. Then we set up eight cameras with orthographic perspective. The orthographic perspective ensures the rendered image fits the isometric world. After setting up the scene, just render the whole animation with eight different cameras and we will get all the bitmap files of the avatar. The benefit is that the rendering process is automatic so that we can reduce the workload a lot. Later if we want to modify the character, we only need to modify it in the 3D software and render it again.

One big disadvantage of using sprite sheet is the file size. The sprite sheets are in bitmap format and one set of animation can cost up to several hundred kilobytes. The file size can be very large when there are many animations and many more bitmaps for switching styles of the avatar.

The other disadvantage is that changing color is quite difficult. Unlike vector rendering where color replacement can be done by ActionScript, we need to replace another bitmap data to change the color. That means every available color doubles the file size.

Rendering avatars using real-time 3D engine

We described how to use 3D software to prerender graphics of the avatars in the previous section. Instead of prerendering the graphics into 2D bitmap, we can integrate a Flash 3D engine to render the 3D model into isometric view in real time.

Real-time 3D rendering is the next trend of Flash. There are several 3D engines available in the market that support rendering complex 3D models with animations. Papervision3D (http://blog.papervision3d.org/) and Away3D (http://away3d.com/) are two examples among them.

The advantage of using 3D rendering in isometric is that the rotation of avatars can be very smooth. Also different textures can share the same model and different models can share the same animation skeleton. Thanks to this great graphic reusability, 3D rendering virtual world can create different combinations of avatar appearance and animations without adding extra graphic workload in development.

However, one disadvantage of using 3D rendering is the Flash player performance. The latest version of Flash player is 10.1 at the time of writing. The following screenshots show that the CPU resources usage is very high when rendering the isometric 3D environment with three avatars on screen:

Rendering avatars using 2D bone skeleton

Bone skeleton used to be an uncommon method to render avatar. What it does is creates an animated skeleton and then glues different parts of body together onto the skeleton. It is somehow similar to the skeleton and mesh relationship in 3-D software but in two dimensions instead. A lot of mathematics is needed to calculate the position and rotation of each part of the body and make the implementation difficult.

Thanks to the introduction of bone tool and inverse kinematics in Flash CS4, this technique is becoming more mature and easier to be used in the Flash world. Adobe has posted a tutorial about using bone tool to create a 2D character (http://www.adobe.com/devnet/flash/articles/character_animation_ik.html).

The following screenshot shows another bone skeleton example from gotoAndPlay demonstrating how to glue the parts into a walking animation. The post can be found in this link: http://www.gotoandplay.it/_articles/2007/04/skeletal_animation.php

The advantage of using 2D bone skeleton is that animations are controlled by ActionScript. The reusing of animations means this technique fits those game designs that require many animations. A dancing virtual world that requires a lot of different unique animations is one example that may need this technique.

One disadvantage is that the large amount of mathematic calculation for the animations makes it difficult to implement.

Every rendering methods has its own advantages and disadvantages and not one of the methods fits all type of games. It is the game designer’s job to decide a suitable rendering method for a game or virtual world project. Therefore, it is important to know their limitations and consider thoughtfully before getting started with development.

We can take a look at how other Flash virtual worlds render avatars by checking the showcase of the SmartFoxServer (http://www.smartfoxserver.com/showcase/).

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