Add Length type.

svg/length.go

@@ -0,0 +1,61 @@
+package svg
+
+type Unit string
+
+// Relative units are:
+// em: the 'font-size' of the relevant font
+// ex: the 'x-height' of the relevant font
+// px: pixels, relative to the viewing device
+// ebisvg uses exactly one ebiten pixel for px unit.
+// const UnitEx = Unit(ex)
+// As the CSS2 standard states "1px thus corresponds to about 0.28 mm"
+// This then means that there are 3.571428571428571 pixels per mm.
+// ebisvg uses this scale factor for the absolute SVG units.
+//
+const MM2PX = 3.571428571428571
+const IN2MM = 254
+const PT2IN = 1 / 72
+const PC2IN = 1 / 6
+
+const UnitNo = Unit("")
+const UnitPx = Unit("px")
+const UnitEm = Unit("em")
+const UnitEx = Unit("ex")
+const UnitIn = Unit("in")
+const UnitCm = Unit("cm")
+const UnitMm = Unit("mm")
+const UnitPt = Unit("pt")
+const UnitPc = Unit("pc")
+const UnitPe = Unit("%")
+
+type Length struct {
+	Magnitude float32
+	Unit
+}
+
+func (l Length) Pixels(parent ...float32) float32 {
+
+	switch l.Unit {
+	case UnitNo, UnitPx:
+		return l.Magnitude
+	case UnitEx, UnitEm, UnitPe:
+		if len(parent) > 0 {
+			return l.Magnitude * parent[0]
+		} else {
+			return l.Magnitude
+		}
+
+	case UnitPc:
+		return l.Magnitude * PC2IN * IN2MM * MM2PX
+	case UnitPt:
+		return l.Magnitude * PT2IN * IN2MM * MM2PX
+	case UnitMm:
+		return l.Magnitude * MM2PX
+	case UnitCm:
+		return l.Magnitude * MM2PX * 100
+	case UnitIn:
+		return l.Magnitude * IN2MM * MM2PX
+	default:
+		return l.Magnitude
+	}
+}