added bump map

bumpmap.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"image"
+	"image/color"
+	"math"
+)
+
+// GenerateBumpMap creates a bump map from a heightmap.
+func GenerateBumpMap(heightmap *image.RGBA, width, height int, depth float64) *image.RGBA {
+	bumpMap := image.NewRGBA(image.Rect(0, 0, width, height))
+
+	sobelX := [][]int{
+		{-1, 0, 1},
+		{-2, 0, 2},
+		{-1, 0, 1},
+	}
+
+	sobelY := [][]int{
+		{-1, -2, -1},
+		{0, 0, 0},
+		{1, 2, 1},
+	}
+
+	for y := 1; y < height-1; y++ {
+		for x := 1; x < width-1; x++ {
+			var gx, gy float64
+
+			for i := 0; i < 3; i++ {
+				for j := 0; j < 3; j++ {
+					gray, _, _, _ := heightmap.At(x+i-1, y+j-1).RGBA()
+					intensity := float64(gray >> 8)
+					gx += intensity * float64(sobelX[j][i])
+					gy += intensity * float64(sobelY[j][i])
+				}
+			}
+
+			nx := gx
+			ny := gy
+			nz := 1.0 / depth
+
+			length := math.Sqrt(nx*nx + ny*ny + nz*nz)
+			if length > 0 {
+				nx /= length
+				ny /= length
+				nz /= length
+			}
+
+			r := uint8((nx + 1.0) * 127.5)
+			g := uint8((ny + 1.0) * 127.5)
+			b := uint8(nz * 255.0)
+
+			bumpMap.Set(x, y, color.RGBA{R: r, G: g, B: b, A: 255})
+		}
+	}
+	return bumpMap
+}