From cf9cbe70874801c177ff70dd2c6328888ca25b83 Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Tue, 28 Oct 2014 11:53:18 +0100
Subject: [PATCH] Fixed hill shading for transparent structures a bit. Still
 not optimal.

---
 common/renderer.go | 30 ++++++++++++++++++++++++++----
 common/spans.go    |  6 ++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/common/renderer.go b/common/renderer.go
index 3ca50a3..d5046f3 100644
--- a/common/renderer.go
+++ b/common/renderer.go
@@ -55,6 +55,13 @@ func max(a, b int) int {
 	return b
 }
 
+func max32(a, b int32) int32 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
 func copyData(data []byte) []byte {
 	l := len(data)
 	ndata := make([]byte, l, max(l, 8*1024))
@@ -429,17 +436,32 @@ func (r *Renderer) CreateShadedImage(
 					pix[iofs+2] = background.B
 					pix[iofs+3] = 0xff
 				} else {
-					var y, y1, y2 int32
-					y = r.yBuffer[ofs]
+					y := r.yBuffer[ofs]
+					t := r.tBuffer[ofs]
+
+					opaque := t == nil || t.Top() < y
+
+					var y1, y2 int32
+
 					if x == 0 {
 						y1 = y
 					} else {
 						y1 = r.yBuffer[ofs-1]
+						if opaque {
+							if s := r.tBuffer[ofs-1]; s != nil {
+								y1 = max32(y1, s.Top())
+							}
+						}
 					}
 					if z == 0 {
 						y2 = y
 					} else {
 						y2 = r.yBuffer[ofs+pw]
+						if opaque {
+							if s := r.tBuffer[ofs+pw]; s != nil {
+								y1 = max32(y1, s.Top())
+							}
+						}
 					}
 					d := ((y - y1) + (y - y2)) * 12
 					if d > 36 {
@@ -451,8 +473,8 @@ func (r *Renderer) CreateShadedImage(
 						G: safeColor(int32(col.G) + d),
 						B: safeColor(int32(col.B) + d),
 						A: 0xff}
-					if r.tBuffer[ofs] != nil {
-						col = cols.BlendColors(r.tBuffer[ofs], col, y)
+					if !opaque {
+						col = cols.BlendColors(t, col, y)
 					}
 					pix[iofs] = col.R
 					pix[iofs+1] = col.G
diff --git a/common/spans.go b/common/spans.go
index 00b1738..7623a86 100644
--- a/common/spans.go
+++ b/common/spans.go
@@ -136,6 +136,12 @@ func (s *Span) Len() int {
 	return n
 }
 
+func (s *Span) Top() int32 {
+	for ; s.Next != nil; s = s.Next {
+	}
+	return s.To
+}
+
 func (s *Span) String() string {
 	var buf bytes.Buffer
 	first := true