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Thread: Raytracing steps

  1. #1

    Raytracing steps

    Hi ,

    I have done a simple raytracing engine in Delphi,
    works well, until I have more than one light and set reflections
    on. I think I have problem in steps order...

    There is just for Each Pixel shot a ray
    for x 0 to 640 do
    for y 0 to 480 do
    raytrace ( ray , aColor )

    in Raytrace procedure is

    for i 0 to LightsCount do begin
    1. define shadow ray and shadow value (to variable called "shd")
    2. diffuse shading (simply draw a pixel in intersection point of aColor * shd)
    3. phong shading

    4. reflection ( I find reflection vector and call recursively Raytrace procedure )

    Is it right order ? find shadow / diffuse / phong / reflection / refractions etc.
    When I have two lights, without reflection set ON, it's ok,
    but when I have two lights, with reflections, reflections are not seen...

    Is here anybody that has some experience with raytracing ?

    thanks a lot.

  2. #2

    Raytracing steps

    I don't have any raytracing experience what so ever, but your order looks a bit off to me. Not so much in the order you render, but how your doing it.

    Seems you should calculate ALL light and shadow sources then render. Otherwise your 1st render of the light/shadow source gets removed when you render the 2nd light.

    Of course, I could be way off, as I have little idea of what your actually doing

  3. #3

    Raytracing steps

    Here is my raytrace function that I made a while ago, it handles multiple lights fine (sometimes theres some shadows messed up, but I think thats the optimisations that I've done.) *EDIT* yea, I found that the BBIntersect function is not working like it should in the shadow detection routine. I've modified the code below.

    BTW: a warning to anyone posting code, it was mangling my code when I posted it using the [ pascal ] tags (leaving out lines and whole segments of code), only after lots of trial and error did I figure out that the < and > signs were interfering with the HTML rendering, disable HTML in this post to fix it.

    Function Tscene.Raytrace(Ray: TRay;TraceDepth: integer; var HitPrim, ChangeIndicator: Integer): vector;
    Var I, J, TempHit, TempCh: integer;
    Dist, TempD, Dott: single;
    R: TRay;
    Pos, N: Vector;
    Shad, Diff, Spec: single;
    Hit: boolean;
    C, L: vector;
    Result := Makevector(0,0,0);
    if TraceDepth > 5 then exit;

    Dist := 1000000;
    Hit := false;
    HitPrim := -1;
    ChangeIndicator := -1;
    C := MakeVector(0,0,0);

    if (LRI[Tracedepth].Lastprim > -1) and (Prim[LRI[TraceDepth].LastPrim].Intersect(Ray, Dist) <> 0) then
    Hit := true;
    HitPrim := LRI[TraceDepth].LastPrim;
    ChangeIndicator := HitPrim+1;

    For I := 0 to NumPrims-1 do
    if I <> LRI[TraceDepth].LastPrim then
    if Prim[I].BBIntersect(Ray) then
    if (Prim[I].Intersect(Ray, Dist) <> 0) then
    Hit := true;
    HitPrim := I;
    ChangeIndicator := I+1;

    LRI[TraceDepth].LastPrim := HitPrim;

    if Hit then
    R := TRay.Create;

    Pos := VecAdd(Ray.Pos, VecMult(Ray.Dir, Dist));

    for I := 0 to NumLights-1 do

    R.Dir := Normalise(VecSub(Light[I].Pos, Pos));
    R.Pos := VecAdd(Pos, VecMult(R.Dir, 0.001));

    Shad := 1;
    TempD := Distance(VecSub(R.Pos, Light[I].Pos));

    if (LRI[Tracedepth].LastShad[I] > -1) and (Prim[LRI[TraceDepth].LastShad[I]].Intersect(R, TempD) <> 0) then
    Shad := 0;
    ChangeIndicator := ChangeIndicator + NumPrims;
    for J := 0 to NumPrims-1 do
    if J <> HitPrim then
    //if Prim[I].BBIntersect(R) then
    if Prim[J].Intersect(R, TempD) <> 0 then
    Shad := 0;
    ChangeIndicator := ChangeIndicator + NumPrims;
    LRI[TraceDepth].LastShad[I] := J;

    if Shad > 0 then
    N := Prim[HitPrim].GetNormal(Pos);
    L := Normalise(VecSub(Light[I].Pos, Pos));

    Dott := Dot(L, N); //Diffuse Shading
    if Dott > 0 then
    Diff := Shad*Dott*Prim[HitPrim].Mat.DiffPower;
    C := VecAdd(C, VecMult(VecMult(Light[I].Color, Prim[HitPrim].Mat.Diffuse), Diff));


    if Prim[HitPrim].Mat.Specular > 0 then //Specular Shading
    Dott := Dot(Ray.Dir, VecSub(L, VecMult(N, (Dot(L, N)* 2) )));
    if (Dott > 0) then
    Spec := Power(Dott, 20) * Prim[HitPrim].Mat.Specular * Shad;
    C := VecAdd(c, VecMult(Light[I].Color, Spec));


    if Prim[HitPrim].Mat.Reflect > 0 then //Reflection
    // Tr := TRay.Create;

    N := Prim[HitPrim].GetNormal(Pos);
    R.Dir := VecSub(Ray.Dir, VecMult(N, 2*Dot(Ray.Dir, N)));
    R.Pos := VecAdd(Pos, Vecmult(R.Dir, 0.01));

    C := VecAdd(C,
    VecMult(Raytrace(R, TraceDepth+1, TempHit, TempCh),

    HitPrim := TempHit;
    ChangeIndicator := ChangeIndicator+TempCh;

    If C[0] > 1 then C[0] := 1;
    If C[1] > 1 then C[1] := 1;
    If C[2] > 1 then C[2] := 1;

    // Blurry Reflections - Tr.Pos := R.Pos;
    // Tr.Dir := R.Dir;
    { if TraceDepth = 0 then
    TempCol := Makevector(0,0,0);

    For I := -1 to 1 do
    for J := -1 to 1 do
    Tr.Dir[0] := I*0.01;
    Tr.Dir[1] := J*0.01;
    Tr.Dir[2] := 0;
    Tr.Dir := VecAdd(Tr.Dir, R.Dir);

    TempCol := VecAdd(RayTrace(TR, TraceDepth+1, TempHit, TempCh), TempCol);

    TempCol := VecMult(TempCol, 1/9);

    C := VecAdd(C,
    VecMult(TempCol, //Raytrace(R, TraceDepth+1, TempHit, TempCh),

    Result := C;
    My site: (coming soon)...

    Download Font Studio 4.21 here.

  4. #4

    Raytracing steps

    Some results:

    My site: (coming soon)...

    Download Font Studio 4.21 here.

  5. #5

    Raytracing steps

    Hey Nitrogen, any chance you would post up a simple sample application showing this off. As I said, I've never played with ray tracing, but I'd love to see code around it

  6. #6

    Raytracing steps

    eh that looks very cool

    How long did it take to generate that image?? and what are your specs??
    Coders rule nr 1: Face ur bugz.. dont cage them with code, kill'em with ur cursor.

  7. #7

    Raytracing steps

    Thanks Nitrogen. I guess it's based on tutorial that is on flipcode.
    Looks very good.

    How have you made antialiased result ?? I haven't done antialiasing yet

  8. #8

    Raytracing steps

    I got it...finally, thanks to Nitro again. I noticed that I had a bug because I didn't Add vector of previous color and color after raytracing in the reflection block of code :-) thaanx This was just stupid misstake.

    Here is simple picture of my raytracer :

    render time : 3 seconds,
    2 lights in the scene. ground has reflection set on, both lights
    are casting shadows.

  9. #9
    Legendary Member NecroDOME's Avatar
    Join Date
    Mar 2004
    The Netherlands, Eindhoven

    Raytracing steps

    So.... in what part of a game could you use ray tracing? You don't want to render a frame in 3 seconds, but the results are great! Could raytracing be used for pre-calculated stuff? (lightmapping or something similar)
    NecroSOFT - End of line -

  10. #10

    Raytracing steps

    I'm not going to do a game, just would like to do some software renderer.
    I know that real-time raytracing is possible. I don't know algorithms for this, but somewhere I've seen real-time raytracing...
    but for games is better to use lightmaps I think..

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