Belal's Blog

How to break out of a nested for-loop in Java

2016-04-30T16:52:00.000-07:00

You'd normally think that it's impossible to break out of a double, triple or n-times nest loops in Java without using some convoluted piece of code that involves some kind of boolean checking but it is possible, and it's pretty darn simple. It's just one of those things that you never learned about in your high school or college java class.

Anyway, here it is, with all its beauty:

outerloop: for(int i = 0; i < 20; i++) {

for(int j = 0; j < 10; j++) {

if(i == 10) {

break outerloop;

}

Yes, it's that simple. Who knew you could label loops in Java.

Efficient Vectors in C#

2013-03-02T10:02:00.000-08:00

Making the raytracing made me in an efficiency craze. I had to think about the efficiency for everything. One of the basic things to think about is vectors! Consider the following vectors. In this code, there are three vector structs, each with different x, y, z implementations. The three vectors overload the multiplication, addition, and subtraction operators to apply them to x, y, and z. I created a simple test to see the efficiency of the 3 implementations. The test was very simple it involved two vectors one with the x, y, and z equal to PI and vector with the x, y, and z values set to 1. The vector with the 1 value is multiplied, added, and subtracted with a PI vector in a for loop that goes 1,000,000 times. Here are the results:

Struct	*	+	-
Vec	1665	255	316
Vec2	2104	569	781
Vec3	1603	224	346

The result show that properties are the least efficient way, taking 100% more time.

Online Raytracer

2012-12-24T17:48:00.001-08:00

I have finished 95% percent of the raytracer, and since it is written in C# and doesn't use unsafe code, I could use it with asp.net. A parser interprets XML for the raytracer and produces a final image at the bottom of the page. The online sample lacks textures and meshes, which I plan to add later. Also the documentation of the markup language is not complete, but you can get the hang of it by taking a look at the samples. Everyday I will update the raytracer and parser for the bugs. Please use the report page to report any bug or exception that comes up! You can find the website here.

Update: More raytracer images

2012-09-17T15:50:00.000-07:00

I haven't posted in a while. Today I will not post much except some more of images of my C# raytracer. I have added reflection, transparency, and textures.
Here are the images:

Break: Calculating perfect numbers

2012-09-07T18:03:00.000-07:00

Till now there have been 4 perfect numbers discovered, but it would be also nice to know how to calculate them. The logic is very simple. I will write the logic and code in C++/CLI.
First lets define perfect numbers. Perfect numbers are numbers that are equal to their divisors. For example number 6, its divisors are 1,2,3 (excluding the number itself). 1 + 2 + 3 = 6. There are about 47 perfect numbers discovered till now, the first 4 are very easy to get; the rest go from 8 digits to millions of digits. The logic is very simple, Here is the code:

long count = 1;
for( ; ;)
{
long current = 0;
for(long i = count - 1; i > 0; i--)
{
if(count % i == 0) // make sure the current number is divisble with the numbers smaller than it
{
current += i;
}
}
if(current == count)
{
Console::WriteLine(count);
}
count++;
}

C# raytracer from scratch

2012-08-27T12:25:00.001-07:00

I am building a complete C# raytracer. It uses my own math library and it will be part of the Disque Engine. The raytracer is close to completion. Right now it can render the basic shapes such as spheres, cubes, cones, cylinders, disks, rectangles, and triangles. I am also trying to implement a ply file reader so that I can render the Stanford bunny or other standard models. After I finish the raytracer I will post tutorials on how to build your own.

Here are some samples(time format is h:m:s.ms) :

Simple image rendered at 256 samples per pixel, total render time: 00:09:43.838

An image of 1000 random spheres rendered at 121 samples per pixel, total render time: 02:13:45.002

I will provide more samples as the raytracer advances.

How to create a sphere programmatically in XNA

2012-07-12T09:14:00.001-07:00

I "discovered" an easy but silly way to create a sphere programmatically in XNA, it is very simple. The idea came to me when I wanted to create huge planets in XNA to make an endless map. Any way the method is very simple, I don't know If someone knows it or it was used before, but till now it is working and efficient. You can control the resolution or how "round" the sphere is.

The code is written in C# with microsoft's XNA 4.0.

Here is a high resolution sphere in wire frame:

The sphere contains 8100 vertices and 48600 indices.

Code:

    public class Sphere
    {
        VertexPositionColor[] vertices; //later, I will provide another example with VertexPositionNormalTexture
        VertexBuffer vbuffer;
        short[] indices; //my laptop can only afford Reach, no HiDef :(
        IndexBuffer ibuffer;
        float radius;
        int nvertices, nindices;
        BasicEffect effect;
        GraphicsDevice graphicd;
        public Sphere(float Radius, GraphicsDevice graphics)
        {
            radius = Radius;
            graphicd = graphics;
            effect = new BasicEffect(graphicd);
            nvertices = 90 * 90; // 90 vertices in a circle, 90 circles in a sphere
            nindices = 90 * 90 * 6;
            vbuffer = new VertexBuffer(graphics, typeof(VertexPositionNormalTexture), nvertices, BufferUsage.WriteOnly);
            ibuffer = new IndexBuffer(graphics, IndexElementSize.SixteenBits, nindices, BufferUsage.WriteOnly);
            createspherevertices();
            createindices();
            vbuffer.SetData<VertexPositionColor>(vertices);
            ibuffer.SetData<short>(indices);
            effect.VertexColorEnabled = true;
        }
        void createspherevertices()
        {
            vertices = new VertexPositionColor[nvertices];
            Vector3 center = new Vector3(0, 0, 0);
            Vector3 rad = new Vector3((float)Math.Abs(radius), 0, 0);
            for (int x = 0; x < 90; x++) //90 circles, difference between each is 4 degrees
            {
                float difx = 360.0f / 90.0f;
                for (int y = 0; y < 90; y++) //90 veritces, difference between each is 4 degrees 
                {
                    float dify = 360.0f / 90.0f;
                    Matrix zrot = Matrix.CreateRotationZ(MathHelper.ToRadians(y * dify)); rotate vertex around z
                    Matrix yrot = Matrix.CreateRotationY(MathHelper.ToRadians(x * difx)); rotate circle around y
                    Vector3 point = Vector3.Transform(Vector3.Transform(rad, zrot), yrot);//transformation

                    vertices[x + y * 90] = new VertexPositionColor(point, Color.Black);
                }
            }
        }
        void createindices()
        {
            indices = new short[nindices];
            int i = 0;
            for (int x = 0; x < 90; x++)
            {
                for (int y = 0; y < 90; y++)
                {
                    int s1 = x == 89 ? 0 : x + 1;
                    int s2 = y == 89 ? 0 : y + 1;
                    short upperLeft = (short)(x * 90 + y);
                    short upperRight = (short)(s1 * 90 + y);
                    short lowerLeft = (short)(x * 90 + s2);
                    short lowerRight = (short)(s1 * 90 + s2);
                    indices[i++] = upperLeft;
                    indices[i++] = upperRight;
                    indices[i++] = lowerLeft;
                    indices[i++] = lowerLeft;
                    indices[i++] = upperRight;
                    indices[i++] = lowerRight;
                }
            }
        }
        public void Draw(Camera cam) // the camera class contains the View and Projection Matrices
        {
            effect.View = cam.View;
            effect.Projection =  cam.Projection;
            graphicd.RasterizerState = new RasterizerState() { FillMode = FillMode.WireFrame }; // Wireframe as in the picture
            foreach (EffectPass pass in effect.CurrentTechnique.Passes)
            {
                pass.Apply();
                graphicd.DrawUserIndexedPrimitives<VertexPositionColor>(PrimitiveType.TriangleList, vertices, 0, nvertices, indices, 0, indices.Length / 3);
            }
        }
    }