[sdf] Add function to copy source bitmap to distance map.

* src/sdf/ftbsdf.c (bsdf_init_distance_map): New function.

2 files changed, 207 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 73d50efb8..48b028395 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2020-08-20  Anuj Verma  <anujv@iitbhilai.ac.in>
 
+	[sdf] Add function to copy source bitmap to distance map.
+
+	* src/sdf/ftbsdf.c (bsdf_init_distance_map): New function.
+
+2020-08-20  Anuj Verma  <anujv@iitbhilai.ac.in>
+
 	[sdf] Add functions to compute pixel edge distances.
 
 	* src/sdf/ftbsdf.c (compute_edge_distance, bsdf_approximate_edge):
diff --git a/src/sdf/ftbsdf.c b/src/sdf/ftbsdf.c
index 9dc6953b7..da4d9f91e 100644
--- a/src/sdf/ftbsdf.c
+++ b/src/sdf/ftbsdf.c
@@ -494,4 +494,205 @@
     return error;
   }
 
+
+  /**************************************************************************
+   *
+   * @Function:
+   *   bsdf_init_distance_map
+   *
+   * @Description:
+   *   Initialize the distance map according to the '8-point sequential
+   *   Euclidean distance mapping' (8SED) algorithm.  Basically it copies
+   *   the `source` bitmap alpha values to the `distance_map->alpha`
+   *   parameter of `worker`.
+   *
+   * @Input:
+   *   source ::
+   *     Source bitmap to copy the data from.
+   *
+   * @Output:
+   *   worker ::
+   *     Target distance map to copy the data to.
+   *
+   * @Return:
+   *   FreeType error, 0 means success.
+   *
+   */
+  static FT_Error
+  bsdf_init_distance_map( const FT_Bitmap*  source,
+                          BSDF_Worker*      worker )
+  {
+    FT_Error  error = FT_Err_Ok;
+
+    FT_Int    x_diff, y_diff;
+    FT_Int    t_i, t_j, s_i, s_j;
+    FT_Byte*  s;
+    ED*       t;
+
+
+    /* again check the parameters (probably unnecessary) */
+    if ( !source || !worker )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    /* Because of the way we convert a bitmap to SDF, */
+    /* i.e., aligning the source to the center of the */
+    /* target, the target's width and rows must be    */
+    /* checked before copying.                        */
+    if ( worker->width < (FT_Int)source->width ||
+         worker->rows  < (FT_Int)source->rows  )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    /* check pixel mode */
+    if ( source->pixel_mode == FT_PIXEL_MODE_NONE )
+    {
+      FT_ERROR(( "bsdf_copy_source_to_target:"
+                 " Invalid pixel mode of source bitmap" ));
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+#ifdef FT_DEBUG_LEVEL_TRACE
+    if ( source->pixel_mode == FT_PIXEL_MODE_MONO )
+    {
+      FT_TRACE0(( "bsdf_copy_source_to_target:"
+                  " The `bsdf' renderer can convert monochrome\n" ));
+      FT_TRACE0(( "                           "
+                  " bitmaps to SDF but the results are not perfect\n" ));
+      FT_TRACE0(( "                           "
+                  " because there is no way to approximate actual\n" ));
+      FT_TRACE0(( "                           "
+                  " outlines from monochrome bitmaps.  Consider\n" ));
+      FT_TRACE0(( "                           "
+                  " using an anti-aliased bitmap instead.\n" ));
+    }
+#endif
+
+    /* Calculate the width and row differences */
+    /* between target and source.              */
+    x_diff = worker->width - source->width;
+    y_diff = worker->rows - source->rows;
+
+    x_diff /= 2;
+    y_diff /= 2;
+
+    t = (ED*)worker->distance_map;
+    s = source->buffer;
+
+    /* For now we only support pixel mode `FT_PIXEL_MODE_MONO`  */
+    /* and `FT_PIXEL_MODE_GRAY`.  More will be added later.     */
+    /*                                                          */
+    /* [NOTE]: We can also use @FT_Bitmap_Convert to convert    */
+    /*         bitmap to 8bpp.  To avoid extra allocation and   */
+    /*         since the target bitmap can be 16bpp we manually */
+    /*         convert the source bitmap to the desired bpp.    */
+
+    switch ( source->pixel_mode )
+    {
+    case FT_PIXEL_MODE_MONO:
+      {
+        FT_Int  t_width = worker->width;
+        FT_Int  t_rows  = worker->rows;
+        FT_Int  s_width = source->width;
+        FT_Int  s_rows  = source->rows;
+
+
+        for ( t_j = 0; t_j < t_rows; t_j++ )
+        {
+          for ( t_i = 0; t_i < t_width; t_i++ )
+          {
+            FT_Int   t_index = t_j * t_width + t_i;
+            FT_Int   s_index;
+            FT_Int   div, mod;
+            FT_Byte  pixel, byte;
+
+
+            t[t_index] = zero_ed;
+
+            s_i = t_i - x_diff;
+            s_j = t_j - y_diff;
+
+            /* Assign 0 to padding similar to */
+            /* the source bitmap.             */
+            if ( s_i < 0 || s_i >= s_width ||
+                 s_j < 0 || s_j >= s_rows  )
+              continue;
+
+            if ( worker->params.flip_y )
+              s_index = ( s_rows - s_j - 1 ) * source->pitch;
+            else
+              s_index = s_j * source->pitch;
+
+            div = s_index + s_i / 8;
+            mod = 7 - s_i % 8;
+
+            pixel = s[div];
+            byte  = 1 << mod;
+
+            t[t_index].alpha = pixel & byte ? 255 : 0;
+
+            pixel = 0;
+          }
+        }
+      }
+      break;
+
+    case FT_PIXEL_MODE_GRAY:
+      {
+        FT_Int  t_width = worker->width;
+        FT_Int  t_rows  = worker->rows;
+        FT_Int  s_width = source->width;
+        FT_Int  s_rows  = source->rows;
+
+
+        /* loop over all pixels and assign pixel values from source */
+        for ( t_j = 0; t_j < t_rows; t_j++ )
+        {
+          for ( t_i = 0; t_i < t_width; t_i++ )
+          {
+            FT_Int  t_index = t_j * t_width + t_i;
+            FT_Int  s_index;
+
+
+            t[t_index] = zero_ed;
+
+            s_i = t_i - x_diff;
+            s_j = t_j - y_diff;
+
+            /* Assign 0 to padding similar to */
+            /* the source bitmap.             */
+            if ( s_i < 0 || s_i >= s_width ||
+                 s_j < 0 || s_j >= s_rows  )
+              continue;
+
+            if ( worker->params.flip_y )
+              s_index = ( s_rows - s_j - 1 ) * s_width + s_i;
+            else
+              s_index = s_j * s_width + s_i;
+
+            /* simply copy the alpha values */
+            t[t_index].alpha = s[s_index];
+          }
+        }
+      }
+      break;
+
+    default:
+      FT_ERROR(( "bsdf_copy_source_to_target:"
+                 " unsopported pixel mode of source bitmap\n" ));
+
+      error = FT_THROW( Unimplemented_Feature );
+      break;
+    }
+
+  Exit:
+    return error;
+  }
+
+
 /* END */