Add charting facility

1 files changed, 82 insertions, 0 deletions

diff --git a/label.go b/label.go
new file mode 100644
index 0000000..b90d8f3
--- /dev/null
+++ b/label.go
@@ -0,0 +1,82 @@
+package gofpdf
+
+// Adapted from Nice Numbers for Graph Labels by Paul Heckbert from "Graphics
+// Gems", Academic Press, 1990
+
+// Paul Heckbert	2 Dec 88
+
+// https://github.com/erich666/GraphicsGems
+
+// LICENSE
+
+// This code repository predates the concept of Open Source, and predates most
+// licenses along such lines. As such, the official license truly is:
+
+// EULA: The Graphics Gems code is copyright-protected. In other words, you
+// cannot claim the text of the code as your own and resell it. Using the code
+// is permitted in any program, product, or library, non-commercial or
+// commercial. Giving credit is not required, though is a nice gesture. The
+// code comes as-is, and if there are any flaws or problems with any Gems code,
+// nobody involved with Gems - authors, editors, publishers, or webmasters -
+// are to be held responsible. Basically, don't be a jerk, and remember that
+// anything free comes with no guarantee.
+
+import (
+	"math"
+)
+
+// niceNum returns a "nice" number approximately equal to x. The number is
+// rounded if round is true, converted to its ceiling otherwise.
+func niceNum(val float64, round bool) float64 {
+	var nf float64
+
+	exp := int(math.Floor(math.Log10(val)))
+	f := val / math.Pow10(exp)
+	if round {
+		switch {
+		case f < 1.5:
+			nf = 1
+		case f < 3.0:
+			nf = 2
+		case f < 7.0:
+			nf = 5
+		default:
+			nf = 10
+		}
+	} else {
+		switch {
+		case f <= 1:
+			nf = 1
+		case f <= 2.0:
+			nf = 2
+		case f <= 5.0:
+			nf = 5
+		default:
+			nf = 10
+		}
+	}
+	return nf * math.Pow10(exp)
+}
+
+// TickmarkPrecision returns an appropriate precision value for label
+// formatting.
+func TickmarkPrecision(div float64) int {
+	return int(math.Max(-math.Floor(math.Log10(div)), 0))
+}
+
+// Tickmarks returns a slice of tickmarks appropriate for a chart axis and an
+// appropriate precision for formatting purposes. The values min and max will
+// be contained within the tickmark range.
+func Tickmarks(min, max float64) (list []float64, precision int) {
+	if max > min {
+		spread := niceNum(max-min, false)
+		d := niceNum((spread / 4), true)
+		graphMin := math.Floor(min/d) * d
+		graphMax := math.Ceil(max/d) * d
+		precision = TickmarkPrecision(d)
+		for x := graphMin; x < graphMax+0.5*d; x += d {
+			list = append(list, x)
+		}
+	}
+	return
+}