start redoing projections?

engine/hexprisms.go

@@ -0,0 +1,10 @@
+package engine
+
+type HexPrismMap struct {
+	Map map[Point3]*HexPrism
+}
+
+type HexPrism struct {
+	pos Point3
+	hpm *HexPrismMap
+}

engine/projection.go

@@ -0,0 +1,24 @@
+package engine
+
+const (
+	// Oblique projections
+	CabinetProjection  = ParallelProjection{0.5, 0.5}
+	CavalierProjection = ParallelProjection{1, 1}
+
+	// Axonometric projections
+	DimetricProjection  = ParallelProjection{0, 0.5}
+	ElevationProjection = ParallelProjection{0, 0}
+	IsometricProjection = ParallelProjection{0, 0.707106781186548} // 1 ÷ √2
+	TrimetricProjection = ParallelProjection{0, 1}
+	HexPrismProjection  = ParallelProjection{0, 0.816496580927726} // √2 ÷ √3
+)
+
+type ParallelProjection struct {
+	ZX, ZY float64
+}
+
+func (π ParallelProjection) Project(p Point3) (px, py float64) {
+	px = float64(p.X) + π.ZX*float64(p.Z)
+	py = float64(p.Y) + π.ZY*float64(p.Z)
+	return px, py
+}