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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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param float2 idim;

// See MaskFillEllipse.jsl for a description of the coordinate system and
// parameters used by these calculations.  This shader simply performs those
// calculations twice, once with the values for the outer ellipse and again
// with the values for the inner ellipse, then subtracts the 2 coverages.

float ellipsemask(float2 abstco, float2 invarcradii)
{
    float2 absecctco = abstco * invarcradii;
    float ecclensq = dot(absecctco, absecctco);
    float delta = dot(absecctco, invarcradii) * 2.0;
    return clamp(0.5 + (1.0 - ecclensq)/delta, 0.0, 1.0);
}

float mask(float2 tco, float2 odim)
{
    // How far are we from the center?
    //float distance = length(tco);
    float2 abstco = abs(tco);

    float ocov = ellipsemask(abstco, odim);
    float icov = ellipsemask(abstco, idim);

    return clamp(ocov - icov, 0.0, 1.0);
}
