Do the hillshading in alpha layer only

src/map/hillshading.cpp

@@ -59,8 +59,8 @@ static void getSubmatrix(int x, int y, const Matrix &m, SubMatrix &sm)
 	sm.z9 = m.m(bottom, right);
 }
 
-QImage HillShading::render(const Matrix &m, quint8 alpha, double azimuth,
-  double elevation)
+QImage HillShading::render(const Matrix &m, quint8 alpha, double z,
+  double azimuth, double elevation)
 {
 	QImage img(m.w() - 2, m.h() - 2, QImage::Format_ARGB32_Premultiplied);
 	uchar *bits = img.bits();
@@ -69,7 +69,6 @@ QImage HillShading::render(const Matrix &m, quint8 alpha, double azimuth,
 	Constants c;
 	SubMatrix sm;
 	Derivatives d;
-	double z = (double)alpha / 0xFF;
 
 	getConstants(azimuth, elevation, c);
 
@@ -86,7 +85,7 @@ QImage HillShading::render(const Matrix &m, quint8 alpha, double azimuth,
 				pixel = 0;
 			else {
 				quint8 val = (L < 0) ? 0 : L * alpha;
-				pixel = alpha<<24 | val<<16 | val<<8 | val;
+				pixel = (alpha - val)<<24;
 			}
 
 			*(quint32*)(bits + (y - 1) * bpl + (x - 1) * 4) = pixel;

src/map/hillshading.h

@@ -7,7 +7,7 @@
 class HillShading
 {
 public:
-	static QImage render(const Matrix &m, quint8 alpha = 64,
+	static QImage render(const Matrix &m, quint8 alpha = 64, double z = 0.3,
 	  double azimuth = 315, double elevation = 25);
 };