Issue #2303 - Please add Constant type of gradient interpolation ...

... to make multi-color hard-edge gradient fills possible

Add a new "step" gradient-segment blending function, which is 0
before the midpoint, and 1 at, and after, the midpoint.  This
creates a hard-edge transition between the two adjacent color stops
at the midpoint.  Creating such a transition was already possible,
but required duplicating the same color at the opposing ends of two
adjacent stops, which is cumbersome.

app/actions/gradient-editor-actions.c

@@ -339,6 +339,11 @@ static const GimpRadioActionEntry gradient_editor_blending_actions[] =
     GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING,
     GIMP_HELP_GRADIENT_EDITOR_BLENDING },
 
+  { "gradient-editor-blending-step", NULL,
+    NC_("gradient-editor-blending", "S_tep"), NULL, NULL,
+    GIMP_GRADIENT_SEGMENT_STEP,
+    GIMP_HELP_GRADIENT_EDITOR_BLENDING },
+
   { "gradient-editor-blending-varies", NULL,
     NC_("gradient-editor-blending", "(Varies)"), NULL, NULL,
     -1,
@@ -826,6 +831,7 @@ gradient_editor_actions_update (GimpActionGroup *group,
   SET_SENSITIVE ("gradient-editor-blending-sine",              editable);
   SET_SENSITIVE ("gradient-editor-blending-sphere-increasing", editable);
   SET_SENSITIVE ("gradient-editor-blending-sphere-decreasing", editable);
+  SET_SENSITIVE ("gradient-editor-blending-step",              editable);
 
   if (blending_equal && gradient)
     {
@@ -846,6 +852,9 @@ gradient_editor_actions_update (GimpActionGroup *group,
         case GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING:
           SET_ACTIVE ("gradient-editor-blending-sphere-decreasing", TRUE);
           break;
+        case GIMP_GRADIENT_SEGMENT_STEP:
+          SET_ACTIVE ("gradient-editor-blending-step", TRUE);
+          break;
         }
     }
   else

app/core/gimpgradient-load.c

@@ -199,7 +199,7 @@ gimp_gradient_load (GimpContext   *context,
         case 2:
           seg->type  = (GimpGradientSegmentType) type;
           if (seg->type < GIMP_GRADIENT_SEGMENT_LINEAR ||
-              seg->type > GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING)
+              seg->type > GIMP_GRADIENT_SEGMENT_STEP)
             {
               g_set_error (error, GIMP_DATA_ERROR, GIMP_DATA_ERROR_READ,
                            _("Corrupt segment %d."), i);

app/core/gimpgradient.c

@@ -90,6 +90,8 @@ static inline gdouble  gimp_gradient_calc_sphere_increasing_factor (gdouble  mid
                                                                     gdouble  pos);
 static inline gdouble  gimp_gradient_calc_sphere_decreasing_factor (gdouble  middle,
                                                                     gdouble  pos);
+static inline gdouble  gimp_gradient_calc_step_factor              (gdouble  middle,
+                                                                    gdouble  pos);
 
 
 G_DEFINE_TYPE_WITH_CODE (GimpGradient, gimp_gradient, GIMP_TYPE_DATA,
@@ -503,6 +505,10 @@ gimp_gradient_get_color_at (GimpGradient                *gradient,
       factor = gimp_gradient_calc_sphere_decreasing_factor (middle, pos);
       break;
 
+    case GIMP_GRADIENT_SEGMENT_STEP:
+      factor = gimp_gradient_calc_step_factor (middle, pos);
+      break;
+
     default:
       g_warning ("%s: Unknown gradient type %d.", G_STRFUNC, seg->type);
       break;
@@ -2273,3 +2279,10 @@ gimp_gradient_calc_sphere_decreasing_factor (gdouble middle,
   /* Works for convex decreasing and concave increasing */
   return 1.0 - sqrt(1.0 - pos * pos);
 }
+
+static inline gdouble
+gimp_gradient_calc_step_factor (gdouble middle,
+                                gdouble pos)
+{
+  return pos >= middle;
+}

libgimpbase/gimpbaseenums.c

@@ -708,6 +708,7 @@ gimp_gradient_segment_type_get_type (void)
     { GIMP_GRADIENT_SEGMENT_SINE, "GIMP_GRADIENT_SEGMENT_SINE", "sine" },
     { GIMP_GRADIENT_SEGMENT_SPHERE_INCREASING, "GIMP_GRADIENT_SEGMENT_SPHERE_INCREASING", "sphere-increasing" },
     { GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING, "GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING", "sphere-decreasing" },
+    { GIMP_GRADIENT_SEGMENT_STEP, "GIMP_GRADIENT_SEGMENT_STEP", "step" },
     { 0, NULL, NULL }
   };
 
@@ -724,6 +725,7 @@ gimp_gradient_segment_type_get_type (void)
     /* Translators: this is an abbreviated version of "Spherical (decreasing)".
        Keep it short. */
     { GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING, NC_("gradient-segment-type", "Spherical (dec)"), NULL },
+    { GIMP_GRADIENT_SEGMENT_STEP, NC_("gradient-segment-type", "Step"), NULL },
     { 0, NULL, NULL }
   };
 

libgimpbase/gimpbaseenums.h

@@ -506,7 +506,8 @@ typedef enum
   GIMP_GRADIENT_SEGMENT_CURVED,             /*< desc="Curved"                                           >*/
   GIMP_GRADIENT_SEGMENT_SINE,               /*< desc="Sinusoidal"                                       >*/
   GIMP_GRADIENT_SEGMENT_SPHERE_INCREASING,  /*< desc="Spherical (increasing)", abbrev="Spherical (inc)" >*/
-  GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING   /*< desc="Spherical (decreasing)", abbrev="Spherical (dec)" >*/
+  GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING,  /*< desc="Spherical (decreasing)", abbrev="Spherical (dec)" >*/
+  GIMP_GRADIENT_SEGMENT_STEP                /*< desc="Step"                                             >*/
 } GimpGradientSegmentType;
 
 

menus/gradient-editor-menu.xml

@@ -85,6 +85,7 @@
       <menuitem action="gradient-editor-blending-sine" />
       <menuitem action="gradient-editor-blending-sphere-increasing" />
       <menuitem action="gradient-editor-blending-sphere-decreasing" />
+      <menuitem action="gradient-editor-blending-step" />
       <menuitem action="gradient-editor-blending-varies" />
     </menu>
     <menu action="gradient-editor-coloring-type">

pdb/enums.pl

@@ -230,12 +230,14 @@ package Gimp::CodeGen::enums;
 			  GIMP_GRADIENT_SEGMENT_CURVED
 			  GIMP_GRADIENT_SEGMENT_SINE
 			  GIMP_GRADIENT_SEGMENT_SPHERE_INCREASING
-			  GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING) ],
+			  GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING
+			  GIMP_GRADIENT_SEGMENT_STEP) ],
 	  mapping => { GIMP_GRADIENT_SEGMENT_LINEAR => '0',
 		       GIMP_GRADIENT_SEGMENT_CURVED => '1',
 		       GIMP_GRADIENT_SEGMENT_SINE => '2',
 		       GIMP_GRADIENT_SEGMENT_SPHERE_INCREASING => '3',
-		       GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING => '4' }
+		       GIMP_GRADIENT_SEGMENT_SPHERE_DECREASING => '4',
+		       GIMP_GRADIENT_SEGMENT_STEP => '5' }
 	},
     GimpGradientType =>
 	{ contig => 1,