/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 Metal Particle System for Metal Shader Showpiece. Initializes the particle system data that is sent to the GPU.

 */

#import "AAPLParticleSystem.h"

static const unsigned int NUM_PARTICLES = 200;

static const float SPREAD = 0.1f;

static const float LIFESPAN = 1.0f;

@implementation AAPLParticleSystem

{

    float* _initialDirection;

    float* _birthOffsets;

}

- (instancetype)initWithDevice:(id <MTLDevice>)device

{

    self = [super init];

    if (self)

    {

        // Allocate and initialize the initial direction buffer

        unsigned int initialDirectionDataSize = NUM_PARTICLES * 3 * sizeof(float);

        _initialDirection = (float*) malloc(initialDirectionDataSize);

        // Set the initial direction as a random vector mostly pointing up with the variable

        // SPREAD controlling the ammount the particles go out from the center.

        for (unsigned int i = 0; i < NUM_PARTICLES; i++) {

            float d_0_x = ( (2.0f * ( (float)rand()/RAND_MAX ) ) - 1.0f) * SPREAD;

            float d_0_y = ( (float)rand()/RAND_MAX );

            float d_0_z = ( (2.0f * ( (float)rand()/RAND_MAX ) ) - 1.0f) * SPREAD;

            float length = sqrtf(d_0_x*d_0_x + d_0_y*d_0_y + d_0_z*d_0_z);

            // Normalize the initial direction vector so the length of the vectoris always

            // one.

            _initialDirection[i*3] = d_0_x / length;

            _initialDirection[i*3+1] = d_0_y / length;

            _initialDirection[i*3+2] = d_0_z / length;

        }

        _initial_direction_buffer = [device newBufferWithBytes:_initialDirection  length:initialDirectionDataSize  options:MTLResourceOptionCPUCacheModeDefault];

        _initial_direction_buffer.label = @"Velocities";

        // Allocate and initialize the birth offsets. These are random numbers between 0 and

        // the lifespan that make it so all the particles don't come out of the emitter at

        // the same time.

        unsigned int birthOffsetsDataSize = NUM_PARTICLES * sizeof(float);

        _birthOffsets = (float*) malloc(birthOffsetsDataSize);

        for (unsigned int i = 0; i < NUM_PARTICLES; i++) {

            _birthOffsets[i] = ( (float)rand()/RAND_MAX ) * LIFESPAN;

        }

        _birth_offsets_buffer = [device newBufferWithBytes:_birthOffsets  length:birthOffsetsDataSize  options:MTLResourceOptionCPUCacheModeDefault];

        _birth_offsets_buffer.label = @"Birth Offsets";

        _num_particles = NUM_PARTICLES;

        _lifespan = LIFESPAN;

    }

    return self;

}

@end