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try to generate at least one tick #264

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79 changes: 40 additions & 39 deletions src/ticks.js
Original file line number Diff line number Diff line change
@@ -1,54 +1,55 @@
var e10 = Math.sqrt(50),
const e10 = Math.sqrt(50),
e5 = Math.sqrt(10),
e2 = Math.sqrt(2);

export default function ticks(start, stop, count) {
var reverse,
i = -1,
n,
ticks,
step;
function tickSpec(start, stop, count) {
const step = (stop - start) / Math.max(0, count),
power = Math.floor(Math.log10(step)),
error = step / Math.pow(10, power),
factor = error >= e10 ? 10 : error >= e5 ? 5 : error >= e2 ? 2 : 1;
let i1, i2, inc;
if (power < 0) {
inc = Math.pow(10, -power) / factor;
i1 = Math.round(start * inc);
i2 = Math.round(stop * inc);
if (i1 / inc < start) ++i1;
if (i2 / inc > stop) --i2;
inc = -inc;
} else {
inc = Math.pow(10, power) * factor;
i1 = Math.round(start / inc);
i2 = Math.round(stop / inc);
if (i1 * inc < start) ++i1;
if (i2 * inc > stop) --i2;
}
if (i2 < i1 && 0.5 <= count && count < 2) return tickSpec(start, stop, count * 2);
return [i1, i2, inc];
}

export default function ticks(start, stop, count) {
stop = +stop, start = +start, count = +count;
if (start === stop && count > 0) return [start];
if (reverse = stop < start) n = start, start = stop, stop = n;
if ((step = tickIncrement(start, stop, count)) === 0 || !isFinite(step)) return [];

if (step > 0) {
let r0 = Math.round(start / step), r1 = Math.round(stop / step);
if (r0 * step < start) ++r0;
if (r1 * step > stop) --r1;
ticks = new Array(n = r1 - r0 + 1);
while (++i < n) ticks[i] = (r0 + i) * step;
if (!(count > 0)) return [];
if (start === stop) return [start];
const reverse = stop < start, [i1, i2, inc] = reverse ? tickSpec(stop, start, count) : tickSpec(start, stop, count);
if (!(i2 >= i1)) return [];
const n = i2 - i1 + 1, ticks = new Array(n);
if (reverse) {
if (inc < 0) for (let i = 0; i < n; ++i) ticks[i] = (i2 - i) / -inc;
else for (let i = 0; i < n; ++i) ticks[i] = (i2 - i) * inc;
} else {
step = -step;
let r0 = Math.round(start * step), r1 = Math.round(stop * step);
if (r0 / step < start) ++r0;
if (r1 / step > stop) --r1;
ticks = new Array(n = r1 - r0 + 1);
while (++i < n) ticks[i] = (r0 + i) / step;
if (inc < 0) for (let i = 0; i < n; ++i) ticks[i] = (i1 + i) / -inc;
else for (let i = 0; i < n; ++i) ticks[i] = (i1 + i) * inc;
}

if (reverse) ticks.reverse();

return ticks;
}

export function tickIncrement(start, stop, count) {
var step = (stop - start) / Math.max(0, count),
power = Math.floor(Math.log(step) / Math.LN10),
error = step / Math.pow(10, power);
return power >= 0
? (error >= e10 ? 10 : error >= e5 ? 5 : error >= e2 ? 2 : 1) * Math.pow(10, power)
: -Math.pow(10, -power) / (error >= e10 ? 10 : error >= e5 ? 5 : error >= e2 ? 2 : 1);
stop = +stop, start = +start, count = +count;
return tickSpec(start, stop, count)[2];
}

export function tickStep(start, stop, count) {
var step0 = Math.abs(stop - start) / Math.max(0, count),
step1 = Math.pow(10, Math.floor(Math.log(step0) / Math.LN10)),
error = step0 / step1;
if (error >= e10) step1 *= 10;
else if (error >= e5) step1 *= 5;
else if (error >= e2) step1 *= 2;
return stop < start ? -step1 : step1;
stop = +stop, start = +start, count = +count;
const reverse = stop < start, inc = reverse ? tickIncrement(stop, start, count) : tickIncrement(start, stop, count);
return (reverse ? -1 : 1) * (inc < 0 ? 1 / -inc : inc);
}
16 changes: 16 additions & 0 deletions test/ticks-test.js
Original file line number Diff line number Diff line change
Expand Up @@ -109,3 +109,19 @@ it("ticks(start, stop, count) returns the reverse of ticks(stop, start, count)",
it("ticks(start, stop, count) handles precision problems", () => {
assert.deepStrictEqual(ticks(0.98, 1.14, 10), [0.98, 1, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14]);
});

it("ticks(start, stop, count) tries to return at least one tick if count >= 0.5", () => {
assert.deepStrictEqual(ticks(1, 364, 0.1), []);
assert.deepStrictEqual(ticks(1, 364, 0.499), []);
assert.deepStrictEqual(ticks(1, 364, 0.5), [200]);
assert.deepStrictEqual(ticks(1, 364, 1), [200]);
assert.deepStrictEqual(ticks(1, 364, 1.5), [200]);
assert.deepStrictEqual(ticks(1, 499, 1), [200, 400]);
assert.deepStrictEqual(ticks(364, 1, 0.5), [200]);
assert.deepStrictEqual(ticks(0.001, 0.364, 0.5), [0.2]);
assert.deepStrictEqual(ticks(0.364, 0.001, 0.5), [0.2]);
assert.deepStrictEqual(ticks(-1, -364, 0.5), [-200]);
assert.deepStrictEqual(ticks(-364, -1, 0.5), [-200]);
assert.deepStrictEqual(ticks(-0.001, -0.364, 0.5), [-0.2]);
assert.deepStrictEqual(ticks(-0.364, -0.001, 0.5), [-0.2]);
});