Working plasma pattern

Signed-off-by: Martyn Ranyard <m@rtyn.berlin>

internal/patterns/plasma.go

@@ -1,9 +1,15 @@
 package patterns
 
-import "math"
+import (
+	"math"
+)
 
 type RGBcolor = [3]byte
 
+func floatColorToIntColor(val float64) byte {
+	return byte(val*256 - 0.5)
+}
+
 func plasmaRGBFromVal(val byte) (byte, byte, byte) {
 	var r byte
 	var g byte
@@ -24,7 +30,6 @@ func plasmaRGBFromVal(val byte) (byte, byte, byte) {
 	return r, g, b
 }
 
-
 func LinearPlasma(l int) []byte {
 	line := make([]byte, l*3)
 	for i := 0; i < l*3; i += 3 {
@@ -37,26 +42,66 @@ func LinearPlasma(l int) []byte {
 	return line
 }
 
-var offset float64 = 0.5
+func linearFromVal(val byte) (byte, byte, byte) {
+	var r byte = val
+	var g byte = 0
+	var b byte = 0
+	return r, g, b
+}
+
+func positiveModF(val float64) float64 {
+	_, val = math.Modf(val)
+	if val < 0 {
+		return val + 1.0
+	}
+	return val
+}
+
+func colorPlasmaFromFloatVal(val float64) (byte, byte, byte) {
+	var r byte
+	var g byte
+	var b byte
+	val = positiveModF(val) * 3.0
+	if val < 1.0 {
+		r = floatColorToIntColor(val)
+		g = floatColorToIntColor(1.0 - val)
+		b = 0
+	} else if val < 2.0 {
+		b = floatColorToIntColor(val - 1.0)
+		r = floatColorToIntColor(1.0 - (val - 1.0))
+		g = 0.0
+	} else {
+		g = floatColorToIntColor(val - 2.0)
+		b = floatColorToIntColor(1.0 - (val - 2.0))
+		r = 0.0
+	}
+	return r, g, b
+}
+
+var palletteOffset float64 = 0.0
 
 func PlasmaPanel(w int, h int, speed uint16) [][]RGBcolor {
 	grid := make([][]RGBcolor, w)
 	for i := 0; i < w; i++ {
 		grid[i] = make([]RGBcolor, h)
 	}
-	scale := math.Pi * 2.0 / float64(w)
-	step := float64(5 * speed / 40)
-	offset -= step
-	if offset < 0 {
-		offset += 1.0
+
+	// pbrook didn't say what DT is for... so it resolves to 0.05
+	palletteOffset -= 0.05 / 1.0
+	if palletteOffset < 0 {
+		palletteOffset += 1.0
 	}
+
+	offset := 0.5 // center offset
+	scale := math.Pi * 2.0 / float64(w)
+
 	for y := 0; y < h; y++ {
 		for x := 0; x < w; x++ {
 			u := math.Cos((float64(x) + offset) * scale)
 			v := math.Cos((float64(y) + offset) * scale)
-			w := math.Cos((float64(w) + offset) * scale)
-			e := (u + v + w + 3.0) / 6.0
-			r, g, b := plasmaRGBFromVal(byte((offset + e) * 255))
+			j := math.Cos(offset * scale) // 2D - No Z
+			e := (u + v + j + 3.0) / 6.0
+			r, g, b := colorPlasmaFromFloatVal(palletteOffset + e)
 			var rgb [3]byte
 			rgb[0] = r
 			rgb[1] = g