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diff --git a/lib/art/art_render_mask.c b/lib/art/art_render_mask.c
new file mode 100644
index 0000000..ce82608
--- /dev/null
+++ b/lib/art/art_render_mask.c
@@ -0,0 +1,168 @@
+/*
+ * art_render_mask.c: Alpha mask source for modular rendering.
+ *
+ * Libart_LGPL - library of basic graphic primitives
+ * Copyright (C) 2000 Raph Levien
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Authors: Raph Levien <raph@acm.org>
+ */
+
+#include "config.h"
+#include "art_render_mask.h"
+
+#include <string.h>
+
+
+typedef struct _ArtMaskSourceMask ArtMaskSourceMask;
+
+struct _ArtMaskSourceMask {
+  ArtMaskSource super;
+  ArtRender *render;
+  art_boolean first;
+  int x0;
+  int y0;
+  int x1;
+  int y1;
+  const art_u8 *mask_buf;
+  int rowstride;
+};
+
+static void
+art_render_mask_done (ArtRenderCallback *self, ArtRender *render)
+{
+  art_free (self);
+}
+
+static int
+art_render_mask_can_drive (ArtMaskSource *self, ArtRender *render)
+{
+  return 0;
+}
+
+static void
+art_render_mask_render (ArtRenderCallback *self, ArtRender *render,
+			art_u8 *dest, int y)
+{
+  ArtMaskSourceMask *z = (ArtMaskSourceMask *)self;
+  int x0 = render->x0, x1 = render->x1;
+  int z_x0 = z->x0, z_x1 = z->x1;
+  int width = x1 - x0;
+  int z_width = z_x1 - z_x0;
+  art_u8 *alpha_buf = render->alpha_buf;
+
+  if (y < z->y0 || y >= z->y1 || z_width <= 0)
+    memset (alpha_buf, 0, width);
+  else
+    {
+      const art_u8 *src_line = z->mask_buf + (y - z->y0) * z->rowstride;
+      art_u8 *dst_line = alpha_buf + z_x0 - x0;
+
+      if (z_x0 > x0)
+	memset (alpha_buf, 0, z_x0 - x0);
+      
+      if (z->first)
+	memcpy (dst_line, src_line, z_width);
+      else
+	{
+	  int x;
+	  
+	  for (x = 0; x < z_width; x++)
+	    {
+	      int v;
+	      v = src_line[x];
+	      if (v)
+		{
+		  v = v * dst_line[x] + 0x80;
+		  v = (v + (v >> 8)) >> 8;
+		  dst_line[x] = v;
+		}
+	      else
+		{
+		  dst_line[x] = 0;
+		}
+	    }
+	}
+      
+      if (z_x1 < x1)
+	memset (alpha_buf + z_x1 - x0, 0, x1 - z_x1);
+    }
+}
+
+static void
+art_render_mask_prepare (ArtMaskSource *self, ArtRender *render,
+			 art_boolean first)
+{
+  ArtMaskSourceMask *z = (ArtMaskSourceMask *)self;
+  self->super.render = art_render_mask_render;
+  z->first = first;
+}
+
+/**
+ * art_render_mask: Use an alpha buffer as a render mask source.
+ * @render: Render object.
+ * @x0: Left coordinate of mask rect.
+ * @y0: Top coordinate of mask rect.
+ * @x1: Right coordinate of mask rect.
+ * @y1: Bottom coordinate of mask rect.
+ * @mask_buf: Buffer containing 8bpp alpha mask data.
+ * @rowstride: Rowstride of @mask_buf.
+ *
+ * Adds @mask_buf to the render object as a mask. Note: @mask_buf must
+ * remain allocated until art_render_invoke() is called on @render.
+ **/
+void
+art_render_mask (ArtRender *render,
+		 int x0, int y0, int x1, int y1,
+		 const art_u8 *mask_buf, int rowstride)
+{
+  ArtMaskSourceMask *mask_source;
+
+  if (x0 < render->x0)
+    {
+      mask_buf += render->x0 - x0;
+      x0 = render->x0;
+    }
+  if (x1 > render->x1)
+    x1 = render->x1;
+
+  if (y0 < render->y0)
+    {
+      mask_buf += (render->y0 - y0) * rowstride;
+      y0 = render->y0;
+    }
+  if (y1 > render->y1)
+    y1 = render->y1;
+
+  mask_source = art_new (ArtMaskSourceMask, 1);
+
+  mask_source->super.super.render = NULL;
+  mask_source->super.super.done = art_render_mask_done;
+  mask_source->super.can_drive = art_render_mask_can_drive;
+  mask_source->super.invoke_driver = NULL;
+  mask_source->super.prepare = art_render_mask_prepare;
+  mask_source->render = render;
+  mask_source->x0 = x0;
+  mask_source->y0 = y0;
+  mask_source->x1 = x1;
+  mask_source->y1 = y1;
+  mask_source->mask_buf = mask_buf;
+  mask_source->rowstride = rowstride;
+
+  art_render_add_mask_source (render, &mask_source->super);
+
+}