From 53991e791a53697aca742c4567121374724bf293 Mon Sep 17 00:00:00 2001
From: Matthew Hague <matthewhague@zoho.com>
Date: Sat, 2 May 2015 12:43:11 +0100
Subject: [PATCH] keep alpha channel on mapnik rendering, scale alpha to alpha
 of mapnik layer

Signed-off-by: Rob Norris <rw_norris@hotmail.com>
---
 src/mapnik_interface.cpp | 34 +++-------------------------------
 src/ui_util.c            | 34 ++++++++++++++++++++++++++++++++++
 src/ui_util.h            |  1 +
 src/vikmapniklayer.c     |  2 +-
 4 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/src/mapnik_interface.cpp b/src/mapnik_interface.cpp
index 6253523f..087e0138 100644
--- a/src/mapnik_interface.cpp
+++ b/src/mapnik_interface.cpp
@@ -189,34 +189,6 @@ gchar* mapnik_interface_load_map_file ( MapnikInterface* mi,
 	return msg;
 }
 
-// These two functions copied from gpsdrive 2.11
-/**
- * convert the color channel
- */
-inline unsigned char
-convert_color_channel (unsigned char Source, unsigned char Alpha)
-{
-	return Alpha ? ((Source << 8) - Source) / Alpha : 0;
-}
-
-/**
- * converting argb32 to gdkpixbuf
- */
-static void
-convert_argb32_to_gdkpixbuf_data (unsigned char const *Source, unsigned int width, unsigned int height, unsigned char *Dest)
-{
-	unsigned char const *SourcePixel = Source;
-	unsigned char *DestPixel = Dest;
-	for (int y = 0; y < height; y++) {
-		for (int x = 0; x < width; x++) {
-			DestPixel[0] = convert_color_channel(SourcePixel[0], SourcePixel[3]);
-			DestPixel[1] = convert_color_channel(SourcePixel[1], SourcePixel[3]);
-			DestPixel[2] = convert_color_channel(SourcePixel[2], SourcePixel[3]);
-			DestPixel += 3;
-			SourcePixel += 4;
-		}
-	}
-}
 
 /**
  * mapnik_interface_render:
@@ -253,11 +225,11 @@ GdkPixbuf* mapnik_interface_render ( MapnikInterface* mi, double lat_tl, double
 		render.apply();
 
 		if ( image.painted() ) {
-			unsigned char *ImageRawDataPtr = (unsigned char *) g_malloc(width * 3 * height);
+			unsigned char *ImageRawDataPtr = (unsigned char *) g_malloc(width * 4 * height);
 			if (!ImageRawDataPtr)
 				return NULL;
-			convert_argb32_to_gdkpixbuf_data(image.raw_data(), width, height, ImageRawDataPtr);
-			pixbuf = gdk_pixbuf_new_from_data(ImageRawDataPtr, GDK_COLORSPACE_RGB, FALSE, 8, width, height, width * 3, NULL, NULL);
+			memcpy(ImageRawDataPtr, image.raw_data(), width * height * 4);
+			pixbuf = gdk_pixbuf_new_from_data(ImageRawDataPtr, GDK_COLORSPACE_RGB, TRUE, 8, width, height, width * 4, NULL, NULL);
 		}
 		else
 			g_warning ("%s not rendered", __FUNCTION__ );
diff --git a/src/ui_util.c b/src/ui_util.c
index ec0976b4..bc061ea5 100644
--- a/src/ui_util.c
+++ b/src/ui_util.c
@@ -211,6 +211,40 @@ GdkPixbuf *ui_pixbuf_set_alpha ( GdkPixbuf *pixbuf, guint8 alpha )
   return pixbuf;
 }
 
+
+/**
+ * Reduce the alpha value of the specified pixbuf by alpha / 255
+ */
+GdkPixbuf *ui_pixbuf_scale_alpha ( GdkPixbuf *pixbuf, guint8 alpha )
+{
+  guchar *pixels;
+  gint width, height, iii, jjj;
+
+  if ( ! gdk_pixbuf_get_has_alpha ( pixbuf ) )
+  {
+    GdkPixbuf *tmp = gdk_pixbuf_add_alpha(pixbuf,FALSE,0,0,0);
+    g_object_unref(G_OBJECT(pixbuf));
+    pixbuf = tmp;
+    if ( !pixbuf )
+      return NULL;
+  }
+
+  pixels = gdk_pixbuf_get_pixels(pixbuf);
+  width = gdk_pixbuf_get_width(pixbuf);
+  height = gdk_pixbuf_get_height(pixbuf);
+
+  /* r,g,b,a,r,g,b,a.... */
+  for (iii = 0; iii < width; iii++) for (jjj = 0; jjj < height; jjj++)
+  {
+    pixels += 3;
+    *pixels = (guint8)(((guint16)*pixels * (guint16)alpha) / 255);
+    pixels++;
+  }
+  return pixbuf;
+}
+
+
+
 /**
  *
  */
diff --git a/src/ui_util.h b/src/ui_util.h
index 2fff065a..42370188 100644
--- a/src/ui_util.h
+++ b/src/ui_util.h
@@ -38,6 +38,7 @@ GtkWidget *ui_lookup_widget(GtkWidget *widget, const gchar *widget_name);
 GtkWidget* ui_label_new_selectable ( const gchar* text );
 
 GdkPixbuf *ui_pixbuf_set_alpha ( GdkPixbuf *pixbuf, guint8 alpha );
+GdkPixbuf *ui_pixbuf_scale_alpha ( GdkPixbuf *pixbuf, guint8 alpha );
 void ui_add_recent_file ( const gchar *filename );
 
 G_END_DECLS
diff --git a/src/vikmapniklayer.c b/src/vikmapniklayer.c
index dc64985d..486125ee 100644
--- a/src/vikmapniklayer.c
+++ b/src/vikmapniklayer.c
@@ -671,7 +671,7 @@ static void render ( VikMapnikLayer *vml, VikCoord *ul, VikCoord *br, MapCoord *
 
 	// NB Mapnik can apply alpha, but use our own function for now
 	if ( vml->alpha < 255 )
-		pixbuf = ui_pixbuf_set_alpha ( pixbuf, vml->alpha );
+		pixbuf = ui_pixbuf_scale_alpha ( pixbuf, vml->alpha );
 	a_mapcache_add ( pixbuf, (mapcache_extra_t){ tt }, ulm->x, ulm->y, ulm->z, MAP_ID_MAPNIK_RENDER, ulm->scale, vml->alpha, 0.0, 0.0, vml->filename_xml );
 }
 
-- 
2.39.5