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Simple Ray Tracing in C#

, 9 Apr 2013 GPL3
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Simple Ray Tracing in C#
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    Introduction

    This article demonstrates how to make a simple and very basic Ray Tracing with spheres; it can serve you as a base for implementing more complex algorithms. In a future article I will show how to improve this using image mapping.

    Background

    The Ray Tracing process is an approach to generate high quality computer graphics, as deeper the level of recursivity interaction with the 3D objects it has more photo realistic appearing.

    The Ray Tracing Algorithm is implemented by calculating the intersection of 3D lines with the 3D objects in the model. The first point of the 3D line we define as the viewer position, the endpoint is located at the projection plane chosen. So for each discrete point at the projection plane an equation for the line is obtained and it is calculated all intersections with all objects selecting the intersection which are nearest to the viewer, so the color is plotted. Using this approach the implemented algorithm can handle opacity, light, shadows and so on.

    3D lines equations can be represented in the form:

    • x = px + t*vx
    • y = py + t*vy
    • z = pz + t*vz

    Where (px,py,pz) are all the points lying in the 3D line, t is a scalar parameter, and (vx,vy,vz) is a direction vector.

    The above equation can be obtained by the definition where a line can be defined by 2 points, so given P1(x1,y1,z1) and P2(x2,y2,z2) we have:

    • v = (x2-x1,y2-y1,z2-z1)

    replacing the found v and p we have:

    • x = x1 + t*(x2-x1)
    • y = y1 + t*(y2-y1)
    • z = z1 + t*(z2-z1)

    So we can be sure that all (x,y,z) which satisfies the above equation belongs to the line defined by P1P2.

    Spheres can be represented in the form:

    • r2 = (x-cx)2+(y-cy)2+(z-cz)2

    where

    • r is the sphere radius
    • (cx,cy,cz) is the center of the sphere

    So we can be sure that all x,y,x points lies on the sphere surface.

    Our objective now is to determine the intersection equation between a given line and a sphere it must be a set of (x,y,z) points which satisfies both equations. It is simple to imagine that a line intersecting a sphere can result 0 intersections, 1 intersection (if tangent) or at most 2 intersections.

    The Equations

    • r2 = (x-cx)2+(y-cy)2+(z-cz)2
    • x = x1 + t*(x2-x1)
    • y = y1 + t*(y2-y1)
    • z = z1 + t*(z2-z1)

    Replacing x, y and z we have:

    • r2 = (x1 + t*(x2-x1)-cx)2 + (y1 + t*(y2-y1) -cy)2 + (z1+ t*(z2-z1)-cz)2

    Let's create a variable for the vector:

    • vx = x2 - x1
    • vy = y2 - y1
    • vz = z2 - z1

    So now we have:

    • r2 = (x1-cx+t*vx)2 + (y1-cy+t*vy)2 + (z1-cz+t*vz)2
    • (x1-cx+t*vx)2 + (y1-cy+t*vy)2 + (z1-cz+t*vz)2 - r2 = 0

    Let's replace (x1,y1,z1) with (px,py,pz) just to simplify...

    Now we have a perfect 2nd degree equation which can give us 0, 1 or 2 different solutions for 't':

    double A = (vx * vx + vy * vy + vz * vz);
    double B = 2.0 * (px * vx + py * vy + pz * vz - vx * cx - vy * cy - vz * cz);
    double C = px * px - 2 * px * cx + cx * cx + py * py - 2 * py * cy + cy * cy +
               pz * pz - 2 * pz * cz    + cz * cz - radius * radius;
    double D = B * B - 4 * A * C;
    double t = -1.0;
    if (D >= 0)
         {
         double t1 = (-B - System.Math.Sqrt(D)) / (2.0 * A);
         double t2 = (-B + System.Math.Sqrt(D)) / (2.0 * A);
         if (t1 > t2)
              t = t1;
         else
              t = t2;  // we choose the nearest t from the first point
         }

    The Source Code

    <script language="C#" runat="server">
    private void Page_Load(object sender, System.EventArgs e)
        {
        Bitmap newBitmap = new Bitmap(200, 200, PixelFormat.Format32bppArgb);
        Graphics g = Graphics.FromImage(newBitmap);
    
        Color clrBackground = Color.Black;
        g.FillRectangle(new SolidBrush(clrBackground), new Rectangle(0, 0, 200,
                        200));
        Rectangle rect = new Rectangle(0, 0, 200, 200);
    
        System.Collections.ArrayList obj3dArrayList;
        obj3dArrayList = new System.Collections.ArrayList();
        obj3dArrayList.Add(new Sphere(0.0, 0.0, 90.0, 100.0, 0.0, 0.0, 255.0));
        obj3dArrayList.Add(new Sphere(-180.0, -130.0, -110.0, 15.0, 255.0, 0.0,
                           0.0));
        obj3dArrayList.Add(new Sphere(-140.0, -140.0, -150.0, 20.0, 255.0, 200.0,
                           0.0));
        Graphics graphics = g;
        // viewer position
        double px = (double)Session["eyex"],
        py = (double)Session["eyey"],
        pz = (double)Session["eyez"];
        // light position
        double lpx = (double)Session["lpx"],
        lpy = (double)Session["lpy"],
        lpz = (double)Session["lpz"];
        // light direction
        double lvx = (double)Session["lvx"],
        lvy = (double)Session["lvy"],
        lvz = (double)Session["lvz"];
        double fMax = 200.0;
        for (int i = rect.Left; i <= rect.Right; i++)
            {
            double x = Sphere.GetCoord(rect.Left, rect.Right, -fMax, fMax, i);
            for (int j = rect.Top; j <= rect.Bottom; j++)
            {
                double y = Sphere.GetCoord(rect.Top, rect.Bottom, fMax, -fMax, j);
                double t = 1.0E10;
                double vx = x - px, vy = y - py, vz = -pz;
                double mod_v = Sphere.modv(vx, vy, vz);
                vx = vx / mod_v;
                vy = vy / mod_v;
                vz = vz / mod_v;
                bool bShadow = false;
                Sphere spherehit = null;
                for (int k = 0; k < (int)obj3dArrayList.Count; k++)
                    {
                    Sphere sphn = (Sphere)obj3dArrayList[k];
                    double taux = Sphere.GetSphereIntersec(sphn.cx, sphn.cy,
                                  sphn.cz,
                                  sphn.radius, px, py, pz, vx, vy, vz);
                    if (taux < 0) continue;
                    if (taux > 0 && taux < t)
                    {
                        t = taux;
                        spherehit = sphn;
                    }
                }
                Color color = Color.FromArgb(10, 20, 10);
                if (spherehit != null)
                {
                    double itx = px + t * vx, ity = py + t * vy, itz = pz +
                    t * vz;
                    // shadow
                    double tauxla = Sphere.GetSphereIntersec(spherehit.cx,
                                    spherehit.cy, spherehit.cz, spherehit.radius,
                                    lpx, lpy, lpz, itx - lpx,
                                    ity - lpy, itz - lpz);
    
                    for (int k = 0; k < (int)obj3dArrayList.Count; k++)
                    {
                        Sphere sphnb = (Sphere)(obj3dArrayList[k]);
                        if (sphnb != spherehit)
                        {
                            double tauxlb = Sphere.GetSphereIntersec(sphnb.cx,
                                            sphnb.cy, sphnb.cz, sphnb.radius, lpx,
                                            lpy, lpz, itx - lpx, ity - lpy, itz -
                                            lpz);
                            if (tauxlb > 0 && tauxla < tauxlb)
                            {
                                bShadow = true;
                                break;
                            }
                        }
                    }
                    double cost = Sphere.GetCosAngleV1V2(lvx, lvy, lvz, itx -
                                  spherehit.cx, ity - spherehit.cy, itz -
                                  spherehit.cz);
                    if (cost < 0) cost = 0;
                    double fact = 1.0;
                    if (bShadow == true) fact = 0.5; else fact = 1.0;
                    double rgbR = spherehit.clR * cost * fact;
                    double rgbG = spherehit.clG * cost * fact;
                    double rgbB = spherehit.clB * cost * fact;
                    color = Color.FromArgb((int)rgbR, (int)rgbG, (int)rgbB);
                    pen = new Pen(color);
                }
                Brush brs = new SolidBrush(color);
                graphics.FillRectangle(brs, i, j, 1, 1);
                brs.Dispose();
    
            }// for pixels lines
        }// for pixels columns
        ///////////////////////////////////////
        MemoryStream tempStream = new MemoryStream();
        newBitmap.Save(tempStream, ImageFormat.Png);
        Response.ClearContent();
        Response.ContentType = "image/png";
        Response.BinaryWrite(tempStream.ToArray());
        Response.Flush();
        }
    </script>

    The Sphere Class

    public class Sphere
    {
        public Sphere(double x, double y, double z, double r, double clr,
                      double clg, double clb)
        {
            cx = x;
            cy = y;
            cz = z;
            radius = r;
            clR = clr;
            clG = clg;
            clB = clb;
        }
        public static double GetCoord(double i1, double i2, double w1, double w2,
            double p)
        {
            return ((p - i1) / (i2 - i1)) * (w2 - w1) + w1;
        }
        public static double modv(double vx, double vy, double vz)
        {
            return System.Math.Sqrt(vx * vx + vy * vy + vz * vz);
        }
        void Move(double vx, double vy, double vz)
        {
            cx += vx;
            cy += vy;
            cz += vz;
        }
        void MoveTo(double vx, double vy, double vz)
        {
            cx = vx;
            cy = vy;
            cz = vz;
        }
        void RotX(double angle)
        {
            double y = cy * System.Math.Cos(angle) - cz * System.Math.Sin(angle);
            double z = cy * System.Math.Sin(angle) + cz * System.Math.Cos(angle);
            cy = y;
            cz = z;
        }
        void RotY(double angle)
        {
            double x = cx * System.Math.Cos(angle) - cz * System.Math.Sin(angle);
            double z = cx * System.Math.Sin(angle) + cz * System.Math.Cos(angle);
            cx = x;
            cz = z;
        }
        public static double GetSphereIntersec(double cx, double cy, double cz,
                             double radius, double px, double py, double pz,
                             double vx, double vy, double vz)
        {
            // x-xo 2 + y-yo 2 + z-zo 2 = r 2
            // x,y,z = p+tv
            // At2 + Bt + C = 0
            double A = (vx * vx + vy * vy + vz * vz);
            double B = 2.0 * (px * vx + py * vy + pz * vz - vx * cx - vy *
                       cy - vz * cz);
            double C = px * px - 2 * px * cx + cx * cx + py * py - 2 * py *
                       cy + cy * cy + pz * pz - 2 * pz * cz + cz * cz -
                       radius * radius;
            double D = B * B - 4 * A * C;
            double t = -1.0;
            if (D >= 0)
            {
                double t1 = (-B - System.Math.Sqrt(D)) / (2.0 * A);
                double t2 = (-B + System.Math.Sqrt(D)) / (2.0 * A);
                if (t1 > t2) t = t1; else t = t2;
            }
            return t;
        }
        public static double GetCosAngleV1V2(double v1x, double v1y, double v1z,
                                             double v2x, double v2y, double v2z)
        {
            /* incident angle
             intersection pt (i)
            double ix, iy, iz;
            ix = px+t*vx;
            iy = py+t*vy;
            iz = pz+t*vz;
            normal at i
            double nx, ny, nz;
            nx = ix - cx;
            ny = iy - cy;
            nz = iz - cz;
    
            cos(t) = (v.w) / (|v|.|w|)
            */
            return (v1x * v2x + v1y * v2y + v1z * v2z) / (modv(v1x, v1y, v1z) *
                   modv(v2x, v2y, v2z));
        }
        public double cx, cy, cz, radius, clR, clG, clB;
    }

License

This article, along with any associated source code and files, is licensed under The GNU General Public License (GPLv3)

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Comments and Discussions

 
QuestionCan you recommend some resource for a newbie who wants to learn ray tracing? PinprofessionalShao Voon Wong2-Sep-14 16:55 
QuestionCode Error PinmemberAmin al-Zanki18-Nov-12 7:33 
GeneralMy vote of 5 Pinmembermanoj kumar choubey26-Feb-12 21:15 
QuestionMy 5* PinmemberThomas.D Williams13-Aug-11 23:23 
GeneralMy vote of 5 Pinmembermanu_221b28-Jul-11 0:55 
QuestionCan you help me please????? Pinmemberbobbyn9513-Jan-09 23:58 
Computer Graphics & Image Processing
 
Ray tracing is a well known technique to light up a scene in computer graphics .It involves the following steps which have to be adhered in order:
 
1. Parsing the scene (3D world) description file and identifying the object areas and filling in the Z buffers.
2. Calculate the ray object intersections.(A single ray is casted from a light source towards the scene)
3. Shade the object surfaces accordingly.
4. Recursive tracing.(A single ray will be reflect and refract through the surfaces. It’s sufficient to trace a ray till its energy becomes minimal or negligible.)
 

You are required to complete and submit the software and the report of the “Simple Ray Tracer” on or before the above mentioned deadline. Please follow the guidelines mentioned below:
 
1. Programming Language:- The best option for an application like this is C or C++ .If you are conversant in using the .NET platform you may choose any language which imports with it. JAVA is not recommended for this assignment.
2. Restrictions:-You cannot use any of the graphics packages or libraries which come with the language implementations or free to download (These include jME, XNA, OpenGL, JAI and other libraries which are free on net).
3. Mandatory Objects:-The program should be able to handle all the primitive 3D Graphic constructs and objects such as teapots in a textured environment.
4. Optional Objects and Effects:-If you could include features such as shadows, shading illumination, view frustum culling and transparency it will be regarded as a plus point.
5. Approach:-When developing the Ray Tracer the following guidelines will help you successfully complete it.
• Have a good idea what ray trcing is and find the equation(s) relating to this particular method.(Specially energy functions)
• Create a simple object and try o create matrices which will contain the distances from the light source.
• When shooting rays at first keep the light in equal grounds with the scene and once you succeed in doing so change the angle and the position.
• Also note that the energy of the bouncing ray is dependent on the surface it last bounced off. So surface properties do matter.
AnswerRe: Can you help me please????? Pinmemberandalmeida14-Jan-09 0:27 
GeneralRe: Can you help me please????? Pinmemberbobbyn9515-Jan-09 14:30 
GeneralNice nice nice PinmemberWindmiller13-Sep-07 1:09 
GeneralRe: Nice nice nice Pinmemberandalmeida13-Sep-07 2:07 

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