• 08/20/15 07:46 AM
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    The Challenge of Having Both Responsiveness and Naturalness in Game Animation

    Visual Arts

    Sector0
    • Posted By Sector0
    Video games as software need to meet functional requirements and it's obvious that the most important functional requirement of a video game is to provide entertainment. Users want to have interesting moments while playing video games and there exists many factors which can bring this entertainment to the players. One of the important factors is the animations within the game. Animation is important because it can affect the game from different aspects. Beauty, controls, narration and driving the logic of the game are among them. This post is trying to consider the animations in terms of responsiveness while trying to discuss some techniques to retain their naturalness as well. In this article I'm going to share some tips we used in the animations of the action-platforming side-scroller game named "Shadow Blade: Reload". SB:R is powered by Unity3D. The PC version has been released 10th 2015 August via Steam and the console versions are on the way. So before going further, let's have a look at some parts of the gameplay here:
    You may want to check the Steam page too. So here we can discuss the problem. First, consider a simple example in real world. You want to punch into a punching bag. You rotate your hip, torso and shoulder in order and consume energy to rotate and move your different limbs. You are feeling the momentum in your body limbs and muscles and then you are hearing the punch sound just after landing it into the bag. So you are sensing the momentum with your tactile sensation, hearing different voices and sounds related to your action and seeing the desired motion of your body. Everything is synchronized! You are feeling the whole process with your different senses. Everything is ordinary here and this is what our mind knows as something natural. Now consider another example in a virtual world like a video game. This time you have a controller, you are pressing a button and you want to see a desired motion. This motion can be any animation like a jump or a punch. But this punch is different from the mentioned example in real world because the player is just moving his thumb on the controller and the virtual character should move his whole body in response to it. Each time player presses a button the character should do an appropriate move. If you receive a desired motion with good visual and sounds after pressing each button, we can say that you are going to be merged within the game because it's something almost similar to the example of punching in real world. The synchronous response of the animations, controls and audios help the player feel himself more within the game. He uses his tactile sensation while interacting with the controller, uses his eyesight to see the desired motion and his hearing sensation to hear the audio. Having all these synchronously at the right moment can bring both responsiveness and naturalness which is what we like to see in our games. Now the problem is that when you want to have responsiveness, you have to kill some naturalness in animations. In a game like Shadow Blade: Reload, the responsiveness is very important because any extra move can lead the player to fall of the edges or be killed by enemies. However we need good-looking animations as well. So in the next section some tips are going to be listed which have been used to bring both responsiveness and naturalness into our playable character named Kuro.

    Cases Which Can Help Bring Both Naturalness and Responsiveness into Animations

    Some of the techniques used in "Shadow Blade: Reload" animations are listed here. They have been used to retain naturalness while having responsiveness: 1- Using Additive Animations: Additive animations can be used to show some asynchronous motions on top of the current animations. We used them in different situations to show the momentum over body while not interrupting the player to show different animations. An example is the land animation. After the player fall ends and he reaches the ground, he can continue running or attacking or throwing shurikens without any interruptions or land animations. So we are directly blending the fall with other animations like running. But blending directly between fall and run doesn't provide an acceptable motion. So here we're just adding an additive land animation on top of the run or other animations to show the momentum over upper body. The additive animations just have visual purposes and the player can continue running or doing other actions without any interruption. The video here shows the additive animation used for the purpose of landing momentum on player's body:
    In Unity, the additive animations are calculated with respect to the current animation's first frame. So the additive animation pose in each frame, is equal to the difference of the current frame and the first frame pose. The reference pose of the character is used here to bring more generic additive animation which can be added well on a range of different locomotion animations. This additive animation is not being applied on top of the standing idle animation. Standing idle uses a different animation for land. We also used some other additive animations there. For example a windmill additive animation on spine and hands. It's being played when the character stops and starts running consecutively. It can show momentum to hands and spine. As a side note, the additive animations have to be created carefully. If you are an indie developer with no full-time animator, you can do these kind of modifications like additive animations via some other procedural animation techniques like Inverse Kinematics. For instance an IK chain on spine can be defined and be used for modification. This is true for hands and feet as well. However the IK chain have to be defined carefully as well as the procedural animation of the end effector. 2- Specific Turn Animations: You see turn animations in many games. For instance, pressing the movement button in the opposite direction while running, makes the character slide and turn back. While this animation is very good for many games and brings good felling to the motions, it is not suitable for an action-platforming game like SB:R because you are always moving back and forth on the platforms with low areas and such an extra movement can make you fall unintentionally and it also kills responsiveness. So for turning, we just rotate the character 180 degrees in one frame. But again, rotating the character 180 degrees in just one frame, is not providing a good-looking motion. So here we used two different turn animations. They are showing the character turning and are starting in a direction opposite to character's forward vector and end in a direction equal to character's forward vector. When we turn the character in just one frame, we play this animation and the animation can show the turn completely. It has the same speed of run animation so nothing is just going to be changed in terms of responsiveness and you will just see a turn animation which is showing momentum of a turn motion over the body and it can bring good visuals to the game. One thing which has to be considered here is that the turn animation starts in a direction opposite the character's forward vector so for using this animation we turned off the transitional blending because it can make jerky motions on a root bone while blending. To avoid frame mismatches and foot-skating, we used two different turn animations and played them based on the feet phases in run animation. You may check out the turn animation here:
    3- Slower Enemies: While the main character is very agile, the enemies are not! Their animations have much more frames. This can help us to get the focus of players out from the main character in many situations . You might know that the human eye has a great ability to focus and zoom on different objects. So when you are looking at one enemy you can only see it clearly and not the others. Slower enemy animations with more frames help us to get the focus out from the player at many points. As a side note, I want to say that I was watching a scientific show about human eyes a while ago and it showed that the women eyes has wider view than men and men has better focusing. You might want to check this research if you are interested about this topic. 4- Safe Blending Intervals to Cancel Animations: Assume a grappling animation. It can be started from idle pose and ended in idle pose again. The animation can do its job in its 50% of length. So the rest of its time is just for the character to get back to its idle pose safe and smoothly. At the most times, players don't want to see the animations until their ending point. They prefer to do other actions. In our game, players usually tend to cancel the attack and grappling animations after they kill enemies. They want to run, jump or dash and continue navigating. So for each animation which can be cancelled, we are setting a safe interval for blending which is used as the time to start cancelling current animation(s). This interval provides poses which can be blended well with run, jump, dash or other attacks. It provides less foot-skating, frame mismatches and good velocity blending while blending between animations. 5- Continuous Animations: In SB:R, most of the animations are animated with respect to the animation(s) which is playing with higher probability before them. For example we have run attacks for the player. When animating them, the animators have concatenated one loop of run before it and created the run attack just after that. With this, we can have a good speed blending between source and destination animations because the run attack animation has been created with respect to the original run animation. Also we can retain the speed and responsiveness of the previous animations into the current animation. Another example here is the edge climb which is starting from the wall run animation. 6- Context-Based Combat: In SB:R we have context-based combat which is helping us using different animations based on the current state of the player (moving, standing, jumping, distance and/or direction to enemies). Attacking from each state, causing different animations to be selected which all are preserving almost the same speed and momentum of the player's current state (moving, standing, diving and so on). For instance, we have run attacks, dash attacks, dive attacks, back stabs, Kusarigama grapples and many other animations. All are being started from their respective animations like run, jump, dash and stand and all trying to preserve the previous motion speed and responsiveness. 7- Physically Simulated Cloths as Secondary Motion: Although responsiveness can lower the rate of naturalness but adding some secondary motions like cloth simulations can help solving this issue. In SB:R we have a scarf for the main character Kuro which helps us showing more acceptable motions. 8- Tense Ragdolls and Lower Crossfade Time in Contacts: Removing crossfade transition times in hits and applying more force to the ragdolls can help more in receiving better hit effects. However this is useful in many games not just in our case.

    Conclusion

    Responsiveness vs. naturalness is always a huge challenge in video games and there are ways to achieve both. Most times you have to do trade-offs between both to achieve a decent result. For those who are eager to find more about this topic, I can recommend this good paper from Motion in Games conference: Aline Normoyle, Sophie Jorg, "Trade-offs between Responsiveness and Naturalness for Player Characters", 2014. It shows interesting results about players' responses to animations with different amount of responsiveness and naturalness.

    Article Update Log

    14 August 2015: Initial release 18 August 2015: Added more reference videos to the article 20 August 2015: Minor edits to the texts


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