How to fill an ellipse shape?

Question

I have a function in C++ which draws an ellipse. Now I want to add a fill option to that ellipse. How do I do that? I tried using the flood fill algorithm, but it does not work correctly when the surface already contains paintings.

Here is my current algorithm:

const double TwoPI = ( PI * 2 );
const double Step = ( PI / 180.0f );

for( double i = 0;  i < TwoPI;  i += Step )
{
    float x_offset = ( radiusX * cos( (float) i ) );
    float y_offset = ( radiusY * sin( (float) i ) );

    int x = int( a_X + x_offset );
    int y = int( a_Y + y_offset );

    if( prevX == -1  &&  prevY == -1 )
        Plot( x, y, color );
    else
        Line( prevX, prevY, x, y, color );
}

Answer 1

Well, one idea could be to just traverse half the circle, and instead compute points that are symmetrically placed around ie the y axis. Then draw a horizontal line between them, filling in all the pixels.

Answer 2

You travel in both directions and drow a line from edge to edge Something like this: I did not try to run it.It's just the idea.Its supposed to paint a filled circle.

const double TwoPI = ( PI * 2 );
const double Step = ( PI / 180.0f );
double start=0;
for( double i = 0;  i < TwoPI;  i += Step )
{
    float x_offset = ( radiusX * cos( (float)start+ i ) );
    float y_offset = ( radiusY * sin( (float) start+i ) );

    float x2_offset = ( radiusX * cos( (float)start - i ) );


    int x = int( a_X + x_offset );
    int x2 = int( a_X + x_offset );
    int y = int( a_Y + y_offset );


    Line( x, y, x2, y, color );
}