private void initParticle(Particle particle) {
// Init the position of the particle. This is based on the source position of the particle
// emitter
// plus a configured variance. The random_minus_1_to_1 macro allows the number to be both
// positive
// and negative
particle.position.x =
(float) (sourcePosition.x + sourcePositionVariance.x * random_minus_1_to_1());
particle.position.y =
(float) (sourcePosition.y + sourcePositionVariance.y * random_minus_1_to_1());
particle.startPos.x = sourcePosition.x;
particle.startPos.y = sourcePosition.y;
// Init the direction of the particle. The newAngle is calculated using the angle passed in and
// the
// angle variance.
float newAngle =
(float) degreesToRadians((float) (angle + angleVariance * random_minus_1_to_1()));
// Create a new Vector2 using the newAngle
Vector2 vector = new Vector2((float) Math.cos(newAngle), (float) Math.sin(newAngle));
// Calculate the vectorSpeed using the speed and speedVariance which has been passed in
float vectorSpeed = (float) (speed + speedVariance * random_minus_1_to_1());
// The particles direction vector is calculated by taking the vector calculated above and
// multiplying that by the speed
particle.direction = Vector2.multiply(vector, vectorSpeed);
// Set the default diameter of the particle from the source position
particle.radius = (float) (maxRadius + maxRadiusVariance * random_minus_1_to_1());
particle.radiusDelta = (maxRadius / particleLifespan) * (1.0f / MAXIMUM_UPDATE_RATE);
particle.angle = degreesToRadians((float) (angle + angleVariance * random_minus_1_to_1()));
particle.degreesPerSecond =
degreesToRadians(
(float) (rotatePerSecond + rotatePerSecondVariance * random_minus_1_to_1()));
particle.radialAcceleration = radialAcceleration;
particle.tangentialAcceleration = tangentialAcceleration;
// Calculate the particles life span using the life span and variance passed in
particle.timeToLive =
(float) Math.max(0, particleLifespan + particleLifespanVariance * random_minus_1_to_1());
// Calculate the particle size using the start and finish particle sizes
float particleStartSize =
(float) (startParticleSize + startParticleSizeVariance * random_minus_1_to_1());
float particleFinishSize =
(float) (finishParticleSize + finishParticleSizeVariance * random_minus_1_to_1());
particle.particleSizeDelta =
((particleFinishSize - particleStartSize) / particle.timeToLive)
* (1.0f / MAXIMUM_UPDATE_RATE);
particle.particleSize = Math.max(0, particleStartSize);
// Calculate the color the particle should have when it starts its life. All the elements
// of the start color passed in along with the variance are used to calculate the star color
Color4f start = new Color4f(0, 0, 0, 0);
start.red = (float) (startColor.red + startColorVariance.red * random_minus_1_to_1());
start.green = (float) (startColor.green + startColorVariance.green * random_minus_1_to_1());
start.blue = (float) (startColor.blue + startColorVariance.blue * random_minus_1_to_1());
start.alpha = (float) (startColor.alpha + startColorVariance.alpha * random_minus_1_to_1());
// Calculate the color the particle should be when its life is over. This is done the same
// way as the start color above
Color4f end = new Color4f(0, 0, 0, 0);
end.red = (float) (finishColor.red + finishColorVariance.red * random_minus_1_to_1());
end.green = (float) (finishColor.green + finishColorVariance.green * random_minus_1_to_1());
end.blue = (float) (finishColor.blue + finishColorVariance.blue * random_minus_1_to_1());
end.alpha = (float) (finishColor.alpha + finishColorVariance.alpha * random_minus_1_to_1());
// Calculate the delta which is to be applied to the particles color during each cycle of its
// life. The delta calculation uses the life span of the particle to make sure that the
// particles color will transition from the start to end color during its life time. As the
// game
// loop is using a fixed delta value we can calculate the delta color once saving cycles in the
// update method
particle.color = start;
particle.deltaColor.red =
((end.red - start.red) / particle.timeToLive) * (1.0f / MAXIMUM_UPDATE_RATE);
particle.deltaColor.green =
((end.green - start.green) / particle.timeToLive) * (1.0f / MAXIMUM_UPDATE_RATE);
particle.deltaColor.blue =
((end.blue - start.blue) / particle.timeToLive) * (1.0f / MAXIMUM_UPDATE_RATE);
particle.deltaColor.alpha =
((end.alpha - start.alpha) / particle.timeToLive) * (1.0f / MAXIMUM_UPDATE_RATE);
// Calculate the rotation
float startA = (float) (rotationStart + rotationStartVariance * random_minus_1_to_1());
float endA = (float) (rotationEnd + rotationEndVariance * random_minus_1_to_1());
particle.rotation = startA;
particle.rotationDelta = (endA - startA) / particle.timeToLive;
}