#version 460 core

struct GenericData
{
  //! Delta time
  float dt;

  //! Elapsed time of the application
  float elapsedTime;

  //! Viewport width of the scene (excluding imgui, that means smaller than window)
  uint viewportWidth;

  //! Ditto but for height
  uint viewportHeight;
};


struct ParticleData
{
  vec4 position;
  vec4 rotation;
  vec4 velocity;
  vec4 acceleration;
  vec4 scaleAndDecay;
  float life;
  uint textureIndex;
};

layout (set = 0, binding = 0) uniform GenericDataBuffer
{
  GenericData data;
} genericDataBuffer;


layout(set = 1, binding = 0) uniform CameraData
{
  vec4 position; 
  mat4 vpMat;
  mat4 viewMat;
  mat4 projMat;
} cameraData;

// output buffer not needed
layout (std430, set = 2, binding = 2) coherent restrict buffer ParticlesOutputBuffer
{
  ParticleData data[];
} outputParticles;

layout (std430, set = 2, binding = 4) coherent restrict buffer IndicesData
{
  uint indices[];
};

// between shader stages
layout(location = 0) out struct
{
  vec2 uv; // location = 0

} Out;

vec2 CreateQuad (in uint vertexID)
{
  uint b = 1 << vertexID;
  return vec2 ((0x3 & b) != 0, (0x9 & b) != 0);
}

void main()
{
  // Create a quad and its texture coordinates
  Out.uv = CreateQuad (gl_VertexIndex);
  vec3 vertexPos = vec3 (Out.uv - vec2(0.5f), 0.0f);

  ParticleData particle = outputParticles.data[indices[gl_InstanceIndex]];

  vec3 normalized = normalize (particle.velocity.xyz);
	float angle = atan (normalized.y, normalized.x);
  vec2 particleScaleData = particle.scaleAndDecay.xz; // x and y

	mat4 localModel = mat4 (1.0f);
  localModel[0][0] = particleScaleData.x;
  localModel[1][1] = particleScaleData.y;

  mat4 rotate = mat4(1.0f);
	rotate[0][0] = cos(angle);
  rotate[0][1] = sin(angle);
  rotate[1][0] = -sin(angle);
  rotate[1][1] = cos(angle);
	localModel = rotate * localModel;

	localModel[3] = vec4 (particle.position.xyz, 1.0f);
  gl_Position = cameraData.vpMat * localModel * vec4(vertexPos, 1.0f);
}