Calculate sound value with distance - math

Question

I have a more mathematical than programming question, sorry if I'm not in the right section. In my 2D game, we can move the camera on a map where there are objects that can emit sound, and this sound volume (defined by a float from 0 to 1) must increase when the screen center is near this object. For example, when the object is at the screen center, the sound volume is 1, and when we move away, the volume must decrease. Each object has its own scope value. (for example 1000 pixels).
I don't know how to write a method that can calculate it.
Here is some of my code (which is not the right calculation) :
private function setVolumeWithDistance():Void
{
sound.volume = getDistanceFromScreenCenter() / range;
// So the volume is a 0 to 1 float, the range is the scope in pixels and
// and the getDistanceFromScreenCenter() is the distance in pixels
}
I already have the method which calculates the distance of the object from the center screen :
public function getDistanceFromScreenCenter():Float
{
return Math.sqrt(Math.pow((Cameraman.getInstance().getFocusPosition().x - position.x), 2) +
Math.pow((Cameraman.getInstance().getFocusPosition().y - position.y), 2));

Answer 1

Simple acoustics can help.
Here is the formula for sound intensity from a point source. It follows an inverse square of distance rule. Build that into your code.
You need to consider the mapping between global and screen coordinates. You have to map pixel location on the screen to physical coordinates and back.
Your distance code is flawed. No one should use pow() to square numbers. Yours is susceptible to round off errors.
This code combines the distance calculation, done properly, and attempts to solve the inverse square intensity calculation. Note: Inverse square is singular for zero distance.
package physics;
/**
* Simple model for an acoustic point source
* Created by Michael
* Creation date 1/16/2016.
* #link https://stackoverflow.com/questions/34827629/calculate-sound-value-with-distance/34828300?noredirect=1#comment57399595_34828300
*/
public class AcousticPointSource {
// Units matter here....
private static final double DEFAULT_REFERENCE_INTENSITY = 0.01;
private static final double DEFAULT_REFERENCE_DISTANCE = 1.0;
// Units matter here...
private double referenceDistance;
private double referenceIntensity;
public static void main(String[] args) {
int numPoints = 20;
double x = 0.0;
double dx = 0.05;
AcousticPointSource source = new AcousticPointSource();
for (int i = 0; i < numPoints; ++i) {
x += dx;
Point p = new Point(x);
System.out.println(String.format("point %s intensity %-10.6f", p, source.intensity(p)));
}
}
public AcousticPointSource() {
this(DEFAULT_REFERENCE_DISTANCE, DEFAULT_REFERENCE_INTENSITY);
}
public AcousticPointSource(double referenceDistance, double referenceIntensity) {
if (referenceDistance <= 0.0) throw new IllegalArgumentException("distance must be positive");
if (referenceIntensity <= 0.0) throw new IllegalArgumentException("intensity must be positive");
this.referenceDistance = referenceDistance;
this.referenceIntensity = referenceIntensity;
}
public double distance2D(Point p1) {
return distance2D(p1, Point.ZERO);
}
public double distance2D(Point p1, Point p2) {
double distance = 0.0;
if ((p1 != null) && (p2 != null)) {
double dx = Math.abs(p1.x - p2.x);
double dy = Math.abs(p1.y - p2.y);
double ratio;
if (dx > dy) {
ratio = dy/dx;
distance = dx;
} else {
ratio = dx/dy;
distance = dy;
}
distance *= Math.sqrt(1.0 + ratio*ratio);
if (Double.isNaN(distance)) {
distance = 0.0;
}
}
return distance;
}
public double intensity(Point p) {
double intensity = 0.0;
if (p != null) {
double distance = distance2D(p);
if (distance != 0.0) {
double ratio = this.referenceDistance/distance;
intensity = this.referenceIntensity*ratio*ratio;
}
}
return intensity;
}
}
class Point {
public static final Point ZERO = new Point(0.0, 0.0, 0.0);
public final double x;
public final double y;
public final double z;
public Point(double x) {
this(x, 0.0, 0.0);
}
public Point(double x, double y) {
this(x, y, 0.0);
}
public Point(double x, double y, double z) {
this.x = x;
this.y = y;
this.z = z;
}
#Override
public String toString() {
return String.format("(%-10.4f,%-10.4f,%-10.4f)", x, y, z);
}
}