[gtk/dotted-lines] Implement dashed and dotted underlines

[Matthias Clasen <matthiasc src gnome org>]

commit c890348ad9f48e56297860a06e1181d49436f5f8
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Mar 30 23:31:37 2021 -0400

    Implement dashed and dotted underlines
    
    This is implementing new support in Pango for
    rendering dashed and dotted lines. This is currently
    not very optimized - it is just emitting the a
    rounded clip for each dot.

 gtk/gskpango.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
---
diff --git a/gtk/gskpango.c b/gtk/gskpango.c
index cfe868cb7a..ffaf0987a9 100644
--- a/gtk/gskpango.c
+++ b/gtk/gskpango.c
@@ -127,6 +127,106 @@ gsk_pango_renderer_draw_rectangle (PangoRenderer     *renderer,
                                                   (double)height / PANGO_SCALE));
 }
 
+static void
+gsk_pango_renderer_draw_line (PangoRenderer        *renderer,
+                              PangoRenderPart       part,
+                              PangoRenderLineStyle  style,
+                              int                   x,
+                              int                   y,
+                              int                   width,
+                              int                   height)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+  GdkRGBA rgba;
+  double xx, yy, ww, hh;
+
+  xx = (double)x / PANGO_SCALE;
+  yy = (double)y / PANGO_SCALE;
+  ww = (double)width / PANGO_SCALE;
+  hh = (double)height / PANGO_SCALE;
+
+  get_color (crenderer, part, &rgba);
+  switch (style)
+    {
+    case PANGO_RENDER_LINE_SOLID:
+      gtk_snapshot_append_color (crenderer->snapshot,
+                                 &rgba,
+                                 &GRAPHENE_RECT_INIT (xx, yy, ww, hh));
+      break;
+
+    case PANGO_RENDER_LINE_DOTTED:
+      {
+#if 0
+        GskRoundedRect dot;
+        double d = MIN (ww, hh);
+        graphene_rect_t bounds = GRAPHENE_RECT_INIT (xx, yy, d, d);
+        graphene_size_t rr = GRAPHENE_SIZE_INIT (d/2, d/2);
+        GdkRGBA transparent = { 0.f, 0.f, 0.f, 0.f };
+
+        gsk_rounded_rect_init (&dot, &bounds, &rr, &rr, &rr, &rr);
+
+        gtk_snapshot_push_repeat (crenderer->snapshot,
+                                  &GRAPHENE_RECT_INIT (xx, yy, ww, hh),
+                                  NULL);
+
+        gtk_snapshot_push_rounded_clip (crenderer->snapshot, &dot);
+        gtk_snapshot_append_color (crenderer->snapshot, &rgba, &bounds);
+        gtk_snapshot_pop (crenderer->snapshot);
+        gtk_snapshot_append_color (crenderer->snapshot, &transparent, &GRAPHENE_RECT_INIT (xx + d, yy, 0.5 * 
d, d));
+        gtk_snapshot_pop (crenderer->snapshot);
+#else
+        double d = MIN (ww, hh);
+        double xend = xx + ww;
+
+        gtk_snapshot_push_clip (crenderer->snapshot,
+                                &GRAPHENE_RECT_INIT (xx, yy, ww, hh));
+
+        while (xx <= xend)
+          {
+            GskRoundedRect dot;
+            graphene_rect_t bounds = GRAPHENE_RECT_INIT (xx, yy, d, d);
+            graphene_size_t rr = GRAPHENE_SIZE_INIT (d/2, d/2);
+
+            gsk_rounded_rect_init (&dot, &bounds, &rr, &rr, &rr, &rr);
+            gtk_snapshot_push_rounded_clip (crenderer->snapshot, &dot);
+            gtk_snapshot_append_color (crenderer->snapshot, &rgba, &bounds);
+            gtk_snapshot_pop (crenderer->snapshot);
+            xx += 1.5 * d;
+          }
+
+        gtk_snapshot_pop (crenderer->snapshot);
+#endif
+      }
+      break;
+
+    case PANGO_RENDER_LINE_DASHED:
+      {
+        GskColorStop stops[4];
+        GdkRGBA transparent = { 0.f, 0.f, 0.f, 0.f };
+
+        stops[0].offset = 0;
+        stops[0].color = rgba;
+        stops[1].offset = 0.66;
+        stops[1].color = rgba;
+        stops[2].offset = 0.66;
+        stops[2].color = transparent;
+        stops[3].offset = 1;
+        stops[3].color = transparent;
+
+        gtk_snapshot_append_repeating_linear_gradient (
+                                  crenderer->snapshot,
+                                  &GRAPHENE_RECT_INIT (xx, yy, ww, hh),
+                                  &GRAPHENE_POINT_INIT (xx, yy),
+                                  &GRAPHENE_POINT_INIT (xx + 9 * MIN (ww, hh), yy),
+                                  stops, 4);
+      }
+      break;
+
+    default:
+      g_assert_not_reached ();
+    }
+}
+
 static void
 gsk_pango_renderer_draw_trapezoid (PangoRenderer   *renderer,
                                    PangoRenderPart  part,
@@ -409,6 +509,11 @@ gsk_pango_renderer_prepare_run (PangoRenderer  *renderer,
     }
   else
     text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_UNDERLINE, fg_rgba);
+
+  if (appearance->overline_rgba)
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_OVERLINE, appearance->overline_rgba);
+  else
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_OVERLINE, fg_rgba);
 }
 
 static void
@@ -426,6 +531,7 @@ gsk_pango_renderer_class_init (GskPangoRendererClass *klass)
   renderer_class->draw_trapezoid = gsk_pango_renderer_draw_trapezoid;
   renderer_class->draw_error_underline = gsk_pango_renderer_draw_error_underline;
   renderer_class->draw_shape = gsk_pango_renderer_draw_shape;
+  renderer_class->draw_line = gsk_pango_renderer_draw_line;
   renderer_class->prepare_run = gsk_pango_renderer_prepare_run;
 }