add Random and RandomSeed

Author: psampaz

api.go

@@ -89,3 +89,15 @@ func Shear(x, y float64) {
 func Matrix(a, b, c, d, e, f float64) {
 	gproc.Matrix(a, b, c, d, e, f)
 }
+
+// RandomSeed changes the sequence of numbers generated by Random.
+func RandomSeed(seed int64) {
+	gproc.RandomSeed(seed)
+}
+
+// Random returns, as a float64, a pseudo-random number in [min,max).
+// Random will produce a different sequence of number every time the program runs.
+// To make the generated numbers deterministic, call RandomSeed with a specific seed.
+func Random(min, max float64) float64 {
+	return gproc.Random(min, max)
+}

api_test.go

@@ -90,3 +90,34 @@ func TestBezier(t *testing.T) {
 	gproc = proc.Proc
 	proc.Run(t)
 }
+
+func TestRandom(t *testing.T) {
+	old := gproc
+	defer func() {
+		gproc = old
+	}()
+
+	// Use a specific seed to make tests deterministic
+	RandomSeed(100)
+
+	tests := []struct {
+		min  float64
+		max  float64
+		want float64
+	}{
+		{0, 5, 4.082513468898083},
+		{-5, -0, -0.19869552746956476},
+		{1, 4, 1.181324427195803},
+		{-4, -1, -3.0641855722578617},
+		{0, 0, 0},
+		{-1, -1, -1},
+		{1, 1, 1},
+	}
+	for _, tt := range tests {
+		t.Run("", func(t *testing.T) {
+			if got := Random(tt.min, tt.max); got != tt.want {
+				t.Errorf("Random() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

proc.go

@@ -14,6 +14,7 @@ import (
 	"io"
 	"log"
 	"math"
+	"math/rand"
 	"os"
 	"path/filepath"
 	"strings"
@@ -99,6 +100,12 @@ func newProc(w, h int) *Proc {
 	proc.cfg.th = material.NewTheme(gofont.Collection())
 	proc.stk.cur().stroke.style.Width = 2
 
+	// If Seed is not called, the generator will produce the same sequence of number every time the
+	// program runs, since the default seed is 1 (see rand.Seed).
+	// Setting a different seed everytime the program starts will make the behavior of Random()
+	// similar to Processing/p5.js.
+	rand.Seed(time.Now().UTC().UnixNano())
+
 	return proc
 }
 
@@ -378,3 +385,15 @@ func (p *Proc) Screenshot(fname string) error {
 
 	return nil
 }
+
+// RandomSeed changes the sequence of numbers generated by Random.
+func (p *Proc) RandomSeed(seed int64) {
+	rand.Seed(seed)
+}
+
+// Random returns, as a float64, a pseudo-random number in [min,max).
+// Random will produce a different sequence of number every time the program runs.
+// To make the generated numbers deterministic, call RandomSeed with a specific seed.
+func (p *Proc) Random(min, max float64) float64 {
+	return rand.Float64()*(max-min) + min
+}