Add a -transparent-dim=percent flag to set the extra dimming of transparent materials each depth meter.

common/colors.go

@@ -13,10 +13,14 @@ import (
 	"strings"
 )
 
+// Dim transparent 2% every node.
+const DefaultTransparentDim = 2.0 / 100.0
+
 type Colors struct {
 	Colors         []color.RGBA
 	NameIndex      map[string]int32
 	NumTransparent int32
+	TransparentDim float32
 }
 
 type namedColor struct {
@@ -81,7 +85,8 @@ func ParseColors(filename string) (colors *Colors, err error) {
 	colors = &Colors{
 		Colors:         cs,
 		NameIndex:      nameIndex,
-		NumTransparent: numTransparent}
+		NumTransparent: numTransparent,
+		TransparentDim: DefaultTransparentDim}
 	return
 }
 
@@ -89,13 +94,6 @@ func (colors *Colors) IsTransparent(index int32) bool {
 	return index < colors.NumTransparent
 }
 
-func min(a, b int32) int32 {
-	if a < b {
-		return a
-	}
-	return b
-}
-
 func BlendColor(c1, c2 color.RGBA, a float32) color.RGBA {
 	b := float32(1) - a
 	return color.RGBA{
@@ -113,12 +111,12 @@ func (colors *Colors) BlendColors(span *Span, col color.RGBA, pos int32) color.R
 	if curr == nil {
 		return col
 	}
-	const scale = float32(1) / 100
+	dim := colors.TransparentDim
 	for ; curr != nil; curr = curr.Next {
 		c := colors.Colors[curr.Value]
-		// At least alpha channel attenuation + 2% extra for each depth meter.
-		base := (int32(c.A) * 100) / 255
-		factor := float32(min(100, base+(curr.To-curr.From)*2)) * scale
+		// At least alpha channel attenuation + dim% extra for each depth meter.
+		base := float32(c.A) / 255.0
+		factor := min32f(1.0, base+float32(curr.To-curr.From)*dim)
 		col = BlendColor(c, col, factor)
 	}
 	return col

common/math.go

@@ -34,3 +34,20 @@ func min16(a, b int16) int16 {
 	}
 	return b
 }
+
+func min32f(a, b float32) float32 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func Clamp32f(x, a, b float32) float32 {
+	switch {
+	case x < a:
+		return a
+	case x > b:
+		return b
+	}
+	return x
+}