Disable trapping by default.

Build with ENABLE_TRAPPING to reenable it. Add explanation and
warnings to doc/Devices.htm.

2 files changed, 86 insertions, 48 deletions

diff --git a/base/gxdownscale.c b/base/gxdownscale.c
index 0cf052ad9..489f10a20 100644
--- a/base/gxdownscale.c
+++ b/base/gxdownscale.c
@@ -1595,6 +1595,57 @@ static int get_planar_line_for_trap(void *arg, unsigned char *buf)
     return code;
 }
 
+static int check_trapping(gs_memory_t *memory, int trap_w, int trap_h,
+                          int num_comps, const int *comp_order)
+{
+#ifndef ENABLE_TRAPPING
+    if (trap_w > 0 || trap_h > 0)
+    {
+        dmprintf(memory,
+                 "Trapping is disabled in this build. To enable trapping,\n"
+                 "follow the instructions in the documentation. Please note\n"
+                 "that if you do this, you are responsible for ensuring that\n"
+                 "you have any and all patent licenses that may be required.\n");
+        return gs_error_rangecheck;
+    }
+#endif
+
+    if (trap_w < 0 || trap_h < 0)
+    {
+        dmprintf(memory, "Trapping range must be >= 0");
+        return gs_error_rangecheck;
+    }
+
+    if (trap_w > 0 || trap_h > 0)
+    {
+        if (comp_order == NULL)
+        {
+            emprintf(memory, "Trapping cannot be used without comp_order being defined");
+            return gs_error_rangecheck;
+        }
+
+        /* Check that the comp_order we have been passed is sane */
+        {
+            char comps[GS_CLIENT_COLOR_MAX_COMPONENTS] = { 0 };
+            int i;
+
+            for (i = 0; i < num_comps; i++)
+            {
+                int n = comp_order[i];
+                if (n < 0 || n >= num_comps || comps[n] != 0)
+                    break;
+                comps[n] = 1;
+            }
+            if (i != num_comps)
+            {
+                emprintf(memory, "Illegal component order passed to trapping");
+                return gs_error_rangecheck;
+            }
+        }
+    }
+    return 0;
+}
+
 int gx_downscaler_init_planar(gx_downscaler_t      *ds,
                               gx_device            *dev,
                               gs_get_bits_params_t *params,
@@ -1642,20 +1693,12 @@ int gx_downscaler_init_planar_trapped(gx_downscaler_t      *ds,
     ds->scaled_data = NULL;
     ds->scaled_span = bitmap_raster((dst_bpc*dev->width*upfactor + downfactor-1)/downfactor);
 
-    if (trap_w < 0 || trap_h < 0)
-    {
-        dmprintf(dev->memory, "Trapping range must be >= 0");
-        return gs_error_rangecheck;
-    }
+    code = check_trapping(dev->memory, trap_w, trap_h, num_comps, comp_order);
+    if (code < 0)
+        return code;
 
     if (trap_w > 0 || trap_h > 0)
     {
-        if (comp_order == NULL)
-        {
-            dmprintf(dev->memory, "Trapping cannot be used without comp_order being defined");
-            return gs_error_rangecheck;
-        }
-
         ds->claptrap = ClapTrap_Init(dev->memory, width, dev->height, num_comps, comp_order, trap_w, trap_h, get_planar_line_for_trap, ds);
         if (ds->claptrap == NULL)
         {
@@ -1828,40 +1871,13 @@ int gx_downscaler_init_trapped(gx_downscaler_t   *ds,
     ds->factor     = factor;
     ds->num_planes = 0;
     ds->src_bpc    = src_bpc;
-    
-    if (trap_w < 0 || trap_h < 0)
-    {
-        dmprintf(dev->memory, "Trapping range must be >= 0");
-        return gs_error_rangecheck;
-    }
+
+    code = check_trapping(dev->memory, trap_w, trap_h, num_comps, comp_order);
+    if (code < 0)
+        return code;
 
     if (trap_w > 0 || trap_h > 0)
     {
-        if (comp_order == NULL)
-        {
-            emprintf(dev->memory, "Trapping cannot be used without comp_order being defined");
-            return gs_error_rangecheck;
-        }
-
-        /* Check that the comp_order we have been passed is sane */
-        {
-            char comps[GS_CLIENT_COLOR_MAX_COMPONENTS] = { 0 };
-            int i;
-
-            for (i = 0; i < num_comps; i++)
-            {
-                int n = comp_order[i];
-                if (n < 0 || n >= num_comps || comps[n] != 0)
-                    break;
-                comps[n] = 1;
-            }
-            if (i != num_comps)
-            {
-                emprintf(dev->memory, "Illegal component order passed to trapping");
-                return gs_error_rangecheck;
-            }
-        }
-
         ds->claptrap = ClapTrap_Init(dev->memory, width, dev->height, num_comps, comp_order, trap_w, trap_h, get_line_for_trap, ds);
         if (ds->claptrap == NULL)
         {
diff --git a/doc/Devices.htm b/doc/Devices.htm
index 5694b708e..60339dc3d 100644
--- a/doc/Devices.htm
+++ b/doc/Devices.htm
@@ -731,7 +731,8 @@ to 32760.
 
 <p>The <code>tiffsep</code> device (along with the <code>tiffscaled32</code> and
 <code>psdcmyk</code> devices) can perform rudimentary automatic bitmap
-'trapping' on the final rendered bitmap.
+'trapping' on the final rendered bitmap. This code is disabled by default; see
+the <a href="trapping_patent_note">note</a> below as to why.
 
 <p>Trapping is a process whereby the output is adjusted to minimise the
 visual impact of offsets between each printed plane. Typically this involves
@@ -741,8 +742,8 @@ revealed in the final printout if the different color plates do not exactly
 line up.
 
 <p>This trapping is controlled by 3 device parameters. Firstly the maximum
-X and Y offsets are specified using <tt>-dTrapX=N</tt> and <tt>-dTrapY=N</tt> (where <tt>N</tt> is a
-figure in pixels, before the downscaler is applied).
+X and Y offsets are specified using <tt>-dTrapX=N</tt> and <tt>-dTrapY=N</tt>
+(where <tt>N</tt> is a figure in pixels, before the downscaler is applied).
 
 <p>The final control is to inform the trapping process in what order inks
 should be processed, from darkest to lightest. For a typical CMYK device
@@ -757,7 +758,27 @@ example:
 <blockquote><code>
     gs -sDEVICE=psdcmyk -dTrapX=2 -dTrapY=2 -o out.psd -c "&lt;&lt; [ 4 5 3 1 0 2 ] &gt;&gt; setpagedevice" -f examples\tiger.eps
 </code></blockquote>
-  
+
+<h4><a name="trapping_patent_note"></a>Trapping patents</h4>
+
+<p>Trapping is an technology area encumbered by many patents. Until
+we can convince ourselves that our trapping code is not covered by
+any of these patents, the functionality is disabled by default.</p>
+
+<p>It can be enabled by building with the <tt>ENABLE_TRAPPING</tt>
+define, but before you do so you should convince yourself that
+either:</p>
+
+<ul>
+<li>The trapping code is not covered by any existing patent.
+<li>Any patents that do cover the code are invalid in your
+jurisdiction.
+<li>That you have appropriate patent licenses for any patents
+  that do apply.
+</ul>
+
+<p>You bear full responsibility for choosing to build with
+<tt>ENABLE_TRAPPING</tt>.
 
 <h3><a name="fax"></a>FAX</h3>
 
@@ -804,8 +825,9 @@ colors.  <a href="#tiffsep">See the comments under the <tt>tiffsep</tt> and <tt>
 device about the maximum number of spot colors supported by Ghostscript</a>
 
 <p>
-These devices support the same -dDownScaleFactor= ratios as <tt>tiffsep</tt>. <tt>tiffscaled32</tt>
-supports the same trapping options as <tt>tiffsep</tt>.
+These devices support the same -dDownScaleFactor= ratios as <tt>tiffsep</tt>.
+<tt>psdcmyk</tt> supports the same trapping options as <tt>tiffsep</tt>
+(but see <a href="trapping_patent_note">this note</a>).
 
 <p>
 NOTE: The PSD format is a single image per file format, so you must use the &quot%d&quot