Hello devs,

My current state of the wheel looks like this:


I want a white center that blends into the respective colors towards the circumference.
Here's a snippet from gimpcolorwheel.c

Function : static void paint_ring (GimpColorWheel *wheel, cairo_t *cr) { ...}

Snippet:

for (yy = 0; yy < height; yy++)

    {

      p = buf + yy * width;

      dy = -(yy - center_y);

      for (xx = 0; xx < width; xx++)

        {

          dx = xx - center_x;

          dist = dx * dx + dy * dy;

          if (dist < ((inner-1) * (inner-1)) || dist > ((outer+1) * (outer+1)))

            {

              *p++ = 0;

              continue;

            }

          angle = atan2 (dy, dx);

          if (angle < 0.0)

            angle += 2.0 * G_PI;

          hue = angle / (2.0 * G_PI);

          r = hue;

          g = 1.0;

          b = 1.0;

          hsv_to_rgb (&r, &g, &b);

          *p++ = (((int)floor (r * 255 + 0.5) << 16) |

                  ((int)floor (g * 255 + 0.5) << 8) |

                  (int)floor (b * 255 + 0.5));

        }

    }

this paints the colors of the wheel. Because we need to paint the center white, we have two options: ( I suppose ? )
One is to include a distance from the center that shall be the faintest white from the center  We can choose this distance to be 20% of the radius allocated. This white coloration can be accommodated into the above snippet but what I fail to solve is how to add the transparency ? Should I calculate a separate 'buf' that is then OR-ed (overlaid) with the 'p' buffer to create that effect ?

OR

I can create a smaller circular arc and use radial gradient (white at center and transparent at circumference , radius again 20% ) and overlay onto the same surface used to draw the initial color wheel as shown in the picture above. 

I personally feel, the second option is easier because the first option would require to know how rgb changes when a certain degree of white is added to it. Your views are looked forward to. 
Thanks.

--

Arshdeep Singh
Third Year, Computer Engineering
Delhi Technological University
Ph: +91-9654115614
https://sites.google.com/site/adsingh1729/home