//
// The graphics engine GLScene
//
unit GLS.LinePFX;

(* A PFX whose particles are lines *)

interface

{$I Stage.Defines.inc}

uses
  Winapi.OpenGL,
  System.Classes,
  System.SysUtils,

  Stage.OpenGLTokens,
  GLS.PersistentClasses,
  Stage.VectorGeometry,
  GLS.ParticleFX,
  GLS.Texture,
  GLS.Color,
  GLS.RenderContextInfo,
  GLS.Context,
  Stage.VectorTypes;

type

  // Linear particle.
  TGLLineParticle = class(TGLParticle)
  private
    FDirection: TAffineVector;
    FLength: Single;
  protected
  public
    procedure WriteToFiler(writer: TGLVirtualWriter); override;
    procedure ReadFromFiler(reader: TGLVirtualReader); override;
    // Direction of the line.
    property Direction: TAffineVector read FDirection write FDirection;
    // Length of the line
    property Length: Single read FLength write FLength;
  end;

  (* Polygonal particles FX manager.
    The particles of this manager are made of N-face regular polygon with
    a core and edge color. No texturing is available.
    If you render large particles and don't have T&L acceleration, consider
    using TGLPointLightPFXManager. *)
  TGLLinePFXManager = class(TGLLifeColoredPFXManager)
  private
    Fvx, Fvy: TAffineVector; // NOT persistent
    FNvx, FNvy: TAffineVector; // NOT persistent
    FDefaultLength: Single;
  protected
    function StoreDefaultLength: Boolean;
    function TexturingMode: Cardinal; override;
    procedure InitializeRendering(var rci: TGLRenderContextInfo); override;
    procedure BeginParticles(var rci: TGLRenderContextInfo); override;
    procedure RenderParticle(var rci: TGLRenderContextInfo;
      aParticle: TGLParticle); override;
    procedure EndParticles(var rci: TGLRenderContextInfo); override;
    procedure FinalizeRendering(var rci: TGLRenderContextInfo); override;
  public
    constructor Create(aOwner: TComponent); override;
    destructor Destroy; override;
    class function ParticlesClass: TGLParticleClass; override;
    function CreateParticle: TGLParticle; override;
  published
    property DefaultLength: Single read FDefaultLength write FDefaultLength
      stored StoreDefaultLength;
    property ParticleSize;
    property ColorInner;
    property ColorOuter;
    property LifeColors;
  end;

// ------------------------------------------------------------------
implementation
// ------------------------------------------------------------------

// ------------------
// ------------------ TGLLinePFXManager ------------------
// ------------------

constructor TGLLinePFXManager.Create(aOwner: TComponent);
begin
  inherited;
  FDefaultLength := 1;
end;

destructor TGLLinePFXManager.Destroy;
begin
  inherited Destroy;
end;

class function TGLLinePFXManager.ParticlesClass: TGLParticleClass;
begin
  Result := TGLLineParticle;
end;

function TGLLinePFXManager.CreateParticle: TGLParticle;
begin
  Result := inherited CreateParticle;
  TGLLineParticle(Result).FLength := DefaultLength;
end;

function TGLLinePFXManager.TexturingMode: Cardinal;
begin
  Result := 0;
end;

procedure TGLLinePFXManager.InitializeRendering(var rci: TGLRenderContextInfo);
var
  i: Integer;
  matrix: TGLMatrix;
begin
  inherited;
  gl.GetFloatv(GL_MODELVIEW_MATRIX, @matrix);
  for i := 0 to 2 do
  begin
    Fvx.V[i] := matrix.V[i].X;
    Fvy.V[i] := matrix.V[i].Y;
  end;
  FNvx := VectorNormalize(Fvx);
  FNvy := VectorNormalize(Fvy);
end;

procedure TGLLinePFXManager.BeginParticles(var rci: TGLRenderContextInfo);
begin
  ApplyBlendingMode(rci);
end;

procedure TGLLinePFXManager.RenderParticle(var rci: TGLRenderContextInfo;
  aParticle: TGLParticle);
var
  lifeTime, sizeScale, fx, fy, f: Single;
  inner, outer: TGLColorVector;
  pos, dir, start, stop, dv: TAffineVector;
begin
  lifeTime := CurrentTime - aParticle.CreationTime;
  ComputeColors(lifeTime, inner, outer);
  if ComputeSizeScale(lifeTime, sizeScale) then
    sizeScale := sizeScale * ParticleSize
  else
    sizeScale := ParticleSize;

  pos := aParticle.Position;

  with TGLLineParticle(aParticle) do
  begin
    dir := VectorNormalize(aParticle.Velocity);
    f := Length * 0.5;
  end;

  start := VectorCombine(pos, dir, 1, f);
  stop := VectorCombine(pos, dir, 1, -f);

  fx := VectorDotProduct(dir, FNvy) * sizeScale;
  fy := -VectorDotProduct(dir, FNvx) * sizeScale;

  dv := VectorCombine(Fvx, Fvy, fx, fy);

  gl.Begin_(GL_TRIANGLE_FAN);
  gl.Color4fv(@inner);
  gl.Vertex3fv(@start);
  gl.Color4fv(@outer);
  gl.Vertex3f(start.X + dv.X, start.Y + dv.Y, start.Z + dv.Z);
  gl.Vertex3f(stop.X + dv.X, stop.Y + dv.Y, stop.Z + dv.Z);
  gl.Color4fv(@inner);
  gl.Vertex3fv(@stop);
  gl.Color4fv(@outer);
  gl.Vertex3f(stop.X - dv.X, stop.Y - dv.Y, stop.Z - dv.Z);
  gl.Vertex3f(start.X - dv.X, start.Y - dv.Y, start.Z - dv.Z);
  gl.End_;
end;

procedure TGLLinePFXManager.EndParticles(var rci: TGLRenderContextInfo);
begin
  UnapplyBlendingMode(rci);
end;

procedure TGLLinePFXManager.FinalizeRendering(var rci: TGLRenderContextInfo);
begin
  inherited;
end;

function TGLLinePFXManager.StoreDefaultLength: Boolean;
begin
  Result := (FDefaultLength <> 1);
end;

// ------------------
// ------------------ TGLLineParticle ------------------
// ------------------

procedure TGLLineParticle.WriteToFiler(writer: TGLVirtualWriter);
begin
  inherited WriteToFiler(writer);
  with writer do
  begin
    WriteInteger(0); // Archive Version 0
    Write(FDirection, SizeOf(FDirection));
    WriteFloat(FLength);
  end;
end;

procedure TGLLineParticle.ReadFromFiler(reader: TGLVirtualReader);
var
  archiveVersion: Integer;
begin
  inherited ReadFromFiler(reader);
  archiveVersion := reader.ReadInteger;
  if archiveVersion = 0 then
    with reader do
    begin
      Read(FDirection, SizeOf(FDirection));
      FLength := ReadFloat;
    end
  else
    RaiseFilerException(archiveVersion);
end;

// ------------------------------------------------------------------
initialization
// ------------------------------------------------------------------

RegisterClasses([TGLLineParticle, TGLLinePFXManager]);

end.