[sdf] Fixed corner checks and improved performance.

* src/sdf/ftsdf.c (sdf_generate_bounding_box): Always check for
  corner if two distance (for different curves) are very close.

* src/sdf/ftsdf.c (sdf_conic_to): Added check to figure out if
  the conic can be treated as a line (which happens if the control
  point coincide with any end-point).

  Also, replace tabs `\t` with spaces.

src/sdf/ftsdf.c

@@ -738,6 +738,18 @@
 
     contour = shape->contours;
 
+    /* If the control point coincide with any of the end point */
+    /* then it's a line and should be treated as one to avoid  */
+    /* unnecessary complexity later in the algorithm.          */
+    if ( ( contour->last_pos.x == control_1->x &&
+           contour->last_pos.y == control_1->y ) ||
+         ( control_1->x == to->x &&
+           control_1->y == to->y ) )
+    {
+      sdf_line_to( to, user );
+      goto Exit;
+    }
+
     FT_CALL( sdf_edge_new( memory, &edge ) );
 
     edge->edge_type = SDF_EDGE_CONIC;
@@ -1160,9 +1172,9 @@
     /* we check the deviation of the bezier and stop if it is     */
     /* lower than a pre-defined `threhold` value.                 */
     if ( FT_ABS( 2 * cpos[0].x - 3 * cpos[1].x + cpos[3].x ) < threshold &&
-	 FT_ABS( 2 * cpos[0].y - 3 * cpos[1].y + cpos[3].y ) < threshold &&
+         FT_ABS( 2 * cpos[0].y - 3 * cpos[1].y + cpos[3].y ) < threshold &&
          FT_ABS( cpos[0].x - 3 * cpos[2].x + 2 * cpos[3].x ) < threshold &&
-	 FT_ABS( cpos[0].y - 3 * cpos[2].y + 2 * cpos[3].y ) < threshold )
+         FT_ABS( cpos[0].y - 3 * cpos[2].y + 2 * cpos[3].y ) < threshold )
     {
       split_cubic( cpos );
       goto Append;
@@ -1264,29 +1276,29 @@
           /* Subdivide the curve and add it to the list. */
           {
             FT_26D6_Vec  ctrls[3];
-	    FT_26D6      dx, dy;
-	    FT_UInt      num_splits;
+            FT_26D6      dx, dy;
+            FT_UInt      num_splits;
 
 
             ctrls[0] = edge->start_pos;
             ctrls[1] = edge->control_a;
             ctrls[2] = edge->end_pos;
 
-	    dx = FT_ABS( ctrls[2].x + ctrls[0].x - 2 * ctrls[1].x );
-	    dy = FT_ABS( ctrls[2].y + ctrls[0].y - 2 * ctrls[1].y );
+            dx = FT_ABS( ctrls[2].x + ctrls[0].x - 2 * ctrls[1].x );
+            dy = FT_ABS( ctrls[2].y + ctrls[0].y - 2 * ctrls[1].y );
             if ( dx < dy )
-	      dx = dy;
-
-	    /* Here we calculate the number of necessary bisections. Each */
-	    /* bisection reduces the deviation by exactly 4-fold, hence   */
-	    /* we bisect the bezier until the deviation becomes less than */
-	    /* 1/8th of a pixel. For more details check `ftgrays.c`.      */
-	    num_splits = 1;
-	    while ( dx > ONE_PIXEL / 8 )
-	    {
-	      dx >>= 2;
-	      num_splits <<= 1;
-	    }
+              dx = dy;
+
+            /* Here we calculate the number of necessary bisections. Each */
+            /* bisection reduces the deviation by exactly 4-fold, hence   */
+            /* we bisect the bezier until the deviation becomes less than */
+            /* 1/8th of a pixel. For more details check `ftgrays.c`.      */
+            num_splits = 1;
+            while ( dx > ONE_PIXEL / 8 )
+            {
+              dx >>= 2;
+              num_splits <<= 1;
+            }
 
             error = split_sdf_conic( memory, ctrls, num_splits, &new_edges );
           }
@@ -3316,6 +3328,7 @@
             FT_26D6_Vec          grid_point = zero_vector;
             SDF_Signed_Distance  dist       = max_sdf;
             FT_UInt              index      = 0;
+            FT_16D16             diff       = 0;
 
 
             if ( x < 0 || x >= width )
@@ -3343,7 +3356,7 @@
             if ( dist.distance > sp_sq )
               continue;
 
-            /* square_root the values and fit in a 6.10 fixed-point */
+            /* square_root the values if required */
             if ( USE_SQUARED_DISTANCES )
               dist.distance = square_root( dist.distance );
 
@@ -3355,11 +3368,15 @@
             /* check whether the pixel is set or not */
             if ( dists[index].sign == 0 )
               dists[index] = dist;
-            else if ( dists[index].distance > dist.distance )
-              dists[index] = dist;
-            else if ( FT_ABS( dists[index].distance - dist.distance )
-                        < CORNER_CHECK_EPSILON )
-              dists[index] = resolve_corner( dists[index], dist );
+            else
+            {
+              diff = FT_ABS( dists[index].distance - dist.distance );
+
+              if ( diff <= CORNER_CHECK_EPSILON )
+                dists[index] = resolve_corner( dists[index], dist );
+              else if ( dists[index].distance > dist.distance )
+                dists[index] = dist;
+            }
           }
         }