Function calcTanTransform

src/traces/pie/plot.js:815–826

(textBB, r, ring, halfAngle, midAngle)

}

function calcTanTransform(textBB, r, ring, halfAngle, midAngle) {
    r = Math.max(0, r - 2 * TEXTPAD);

    // max size if text is rotated tangentially
    var a = textBB.height / textBB.width;
    var s = calcMaxHalfSize(a, halfAngle, r, ring);
    return {
        scale: (s * 2) / textBB.width,
        rCenter: calcRCenter(a, s / r),
        rotate: calcRotate(midAngle + Math.PI / 2)
    };
}

function calcRCenter(a, b) {
    return Math.cos(b) - a * b;