Question

    for (iy = 0; iy < h; iy++)
    {
        double angy = (camera.fov_y / h) * iy;
        for (ix = 0; ix < w; ix++)
        {
            double angx = (camera.fov_x / w) * ix;
            //output[ix,iy].r = (int)Math.Round(255 * (angy / camera.fov_y);
            //output[ix,iy].b = (int)Math.Round(255 * (angy / camera.fov_y); 
            double tr = (angx / camera.fov_x) * 255D;
            double tb = (angy / camera.fov_y) * 255D;
            Console.Write("({0},{1})",Math.Round(tr),Math.Round(tb));

            output.SetPixel(ix, iy, Color.FromArgb(Convert.ToInt32(tr), 0, Convert.ToInt32(tb)) );
            Console.Write(".");
        }
        Console.WriteLine();
    }

Can anyone see any immediate problems with that code?
The variables tr and tb always evaluate to 0.

I’m happy to provide more information if it is needed.

Answer 1

You haven’t given the types for the other variables – in particular, what are the types of camera.fov_x and camera.fov_y? If they’re both integers, then the lines initializing angx and angy will be evaluated using integer arithmetic.

This can be fixed by casting one of the operands:

double angy = ((double) camera.fov_y / h) * iy;

The fovy and fovx variables are already doubles though, this isn’t the problem.

Could you give a complete example of this, which we can compile and test ourselves?

EDIT: Koistya Navin’s edit is overkill. You only need one operand of an expression to be a double for the whole thing to be computed using double arithmetic. (It needs to be the right expression though – if you do (a/b) * c and cast c a double, the multiplication will be done with double arithmetic but a/b might still be done as integers.)

Here’s the listing changed appropriately to make sure double arithmetic is used everywhere it should be:

// Changed loops to declare the variable, for stylistic purposes
for (int iy = 0; iy < h; iy++)
{
    // Changed here - cast camera.fov_y
    double angy = ((double) camera.fov_y / h) * iy;
    for (int ix = 0; ix < w; ix++)
    {
        // Changed here - cast camera.fov_x
        double angx = ((double) camera.fov_x / w) * ix;
        //output[ix,iy].r = (int)Math.Round(255 * (angy / camera.fov_y);
        //output[ix,iy].b = (int)Math.Round(255 * (angy / camera.fov_y); 
        double tr = (angx / camera.fov_x) * 255D;
        double tb = (angy / camera.fov_y) * 255D;
        Console.Write("({0},{1})", Math.Round(tr), Math.Round(tb));

        output.SetPixel(ix, iy, Color.FromArgb(Convert.ToInt32(tr), 
                                               0,
                                               Convert.ToInt32(tb)) );
        Console.Write(".");
    }
    Console.WriteLine();
}