{"id":56,"date":"2022-05-24T15:26:03","date_gmt":"2022-05-24T19:26:03","guid":{"rendered":"https:\/\/courses.ideate.cmu.edu\/53-353\/m2022\/?p=56"},"modified":"2022-05-24T15:26:03","modified_gmt":"2022-05-24T19:26:03","slug":"day-7-easy-pong-2-collisions-sound","status":"publish","type":"post","link":"https:\/\/courses.ideate.cmu.edu\/53-353\/m2022\/?p=56","title":{"rendered":"Day 7: Easy Pong 2 (Collisions & Sound)"},"content":{"rendered":"\n

Today we take a look at collisions – when objects bump into one another. These are some of the most commonly used events because so much of our game mechanics depend on whether or not two things have touched. We use them to determine if a hit was successful, if an enemy has touched us, if we are on the ground, if we should be making a sound. Understanding how collision events are generated and how to interpret them is incredibly important. And today, we will use them to generate game feedback in the form of sounds.<\/p>\n\n\n\n\n\n\n\n

It\u2019s fun to watch our ball bounce around, but we should add some sound to really make this pop.\u00a0 I\u2019ve uploaded\u00a0a few sounds to use for this demo (you can find them on Canvas), feel free to use those or a noise of your own creation.\u00a0 Just remember, the sound should be quick, and the noise should start at the very beginning of the file, otherwise you\u2019ll have a brief period of dead air and it will appear as though the sound is delayed.\u00a0 Import your sounds using\u00a0Assets > Import New Asset\u2026<\/strong>, or simply drag the files into the Assets folder.<\/p>\n\n\n\n

Since the only thing in our current design that should make a noise is when the ball collides with something, I\u2019ve decided to assign all noise making duties to the ball itself.  <\/p>\n\n\n\n

In order to make sounds, an object must have the AudioSource Component<\/strong> attached to it, so I add one to the \u201cball\u201d object.  When you add this component, you will notice an empty AudioClip<\/strong> property which is the audio file to be played \u2013 leave this empty, as we will fill it later using our script.You will also notice that, by default, Play On Awake<\/strong> is checked.  De-select this option, as we will control when we want things to play.<\/p>\n\n\n\n

We want our clip to play whenever the ball hits the paddle, so we need to figure out when that event occurs.  To do this, we will test every collision that the ball experiences.   <\/p>\n\n\n\n

Whenever a collision occurs, the game generates a Collision Event<\/strong>.  We can set our scripts to listen for these events and use them to perform actions, in this case playing our sound.  Add a new script to the Ball object (I called mine BallScript<\/strong>.   Add the following code for the variable declaration and Start ( )<\/strong> function:<\/p>\n\n\n\n

private AudioSource audio;\n\/\/ Start is called before the first frame update\nvoid Start()\n{\n    audio = GetComponent<AudioSource>();\n}<\/pre>\n\n\n\n
Just like we created a Rigidbody typed variable, here we create an AudioSource<\/strong> type variable and assign it using GetComponent<AudioSource> ( )<\/strong>.    Notice, however, that before we used a reference to a separate game object (\u201cballobject\u201d) as our source, and here we simply use \u201cthis\u201d.  This<\/strong> gives us access to the object which it is running through.  It is self-referential, so no extra association steps required.<\/p>\n\n\n\n
Our next step is to identify when a collision occurs, then look to see if we have hit the right type<\/em> of collision.<\/p>\n\n\n\n
private void OnCollisionEnter(Collision collision)\n{\n    if(collision.gameObject.tag == \"Wall\")\n    {\n        audio.Play();\n    }\n}<\/pre>\n\n\n\n
OnCollisionEnter ( )<\/strong> runs when a collision event occurs involving this object \u2013 meaning that this object\u2019s collider has initiated contact with another object\u2019s collider. It is only called one time per collision.  When the objects separate \/ stop touching, there is an OnCollisionExit ( )<\/strong> message that will be called.  If objects remain in contact, OnCollisionStay ( )<\/strong> messages will issue once per frame.<\/p>\n\n\n\n
Our collision event has a parameter that is of the type Collision<\/strong>, which here we assign to a variable \u201ccollision\u201d.  This Collision object contains data about the collision, such as the point of contact, the object that was hit, and the relative velocity of the two objects.  Here we test the Tag<\/strong> of the other object against a known value, and if it returns as true, we tell the audioSource to run the Play( ) <\/strong>command.   <\/p>\n\n\n\n
Unity projects have a few pre-existing tags that you can use, but I recommend creating your own.<\/p>\n\n\n\n
Select your paddle prefab, and in the inspector look for the Tag<\/strong> dropdown near the top.  In there, select Add New Tag\u2026<\/strong> and add a new named tag.  Call this one \u201cWall\u201d.  Now select your paddle again and from the dropdown give it the tag Wall<\/strong>.    Now play your game and you should get a satisfying \u201cbonk\u201d noise when your ball hits a wall.  Let’s look a little closer at the Audio Source component:<\/p>\n\n\n\n
\"\"<\/figure><\/div>\n\n\n\n
As the name suggests, this component makes our object the “source” of a bit of audio, by having it emit a sound.   The sound that will be emitted is defined using the AudioClip<\/strong> setting, which gives us access to the AudioSource.clip<\/strong> property.   Once a clip has been set, we can use AudioSource.Play( )<\/strong> to play the sound, and AudioSource.Stop( )<\/strong> to stop it.  <\/p>\n\n\n\n
But the AudioSource is only one half of the equation.  We also need to have an AudioListener<\/strong> <\/a>in our scene, to act as our “ears”.   By default, the AudioListener is added as component on the Main Camera.<\/p>\n\n\n\n
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That’s it.  No properties  to mess around with.  Just a single line in your inspector.<\/figcaption><\/figure><\/div>\n\n\n\n
The reason this configuration makes sense is that your Main Camera is usually your best representation of where you as the observer are in relation to the world of the game itself.  The Spatial<\/strong> slider in your AudioSource component allows you to set the sound to be:<\/p>\n\n\n\n