[dia] Bug 576548 - [cairo] Highlighted text editing

[Hans Breuer <hans src gnome org>]

commit 2aecb70084d0a2f31cf99d3e5dd2224a30858a45
Author: Hans Breuer <hans breuer org>
Date:   Sun Jan 9 19:11:19 2011 +0100

    Bug 576548 - [cairo] Highlighted text editing
    
    Rather than full blown highlighting which spreads across the
    whole renderer, this is just restricted to help text editing.
    And instead of a single text color an alternate one gets used
    if the contrast of the first one is just not strong enough.
    
    This is not using any special drawing capabilities from cairo,
    but could be implemented with the other interactive renderers,
    too.

 plug-ins/cairo/diacairo-interactive.c |   91 +++++++++++++++++++++++++++++++++
 1 files changed, 91 insertions(+), 0 deletions(-)
---
diff --git a/plug-ins/cairo/diacairo-interactive.c b/plug-ins/cairo/diacairo-interactive.c
index ff682cc..3e64d61 100644
--- a/plug-ins/cairo/diacairo-interactive.c
+++ b/plug-ins/cairo/diacairo-interactive.c
@@ -173,6 +173,94 @@ get_text_width(DiaRenderer *object,
   text_line_destroy(text_line);
   return result;
 }
+/** Used as background? for text editing */
+static Color text_edit_color = {1.0, 1.0, 0.7 };
+
+real
+calculate_relative_luminance (const Color *c)
+{
+  real R, G, B;
+
+  R = (c->red <= 0.03928) ? c->red / 12.92 : pow((c->red+0.055)/1.055, 2.4);
+  G = (c->green <= 0.03928) ? c->green / 12.92 : pow((c->green+0.055)/1.055, 2.4);
+  B = (c->blue <= 0.03928) ? c->blue / 12.92 : pow((c->blue+0.055)/1.055, 2.4);
+
+  return 0.2126 * R + 0.7152 * G + 0.0722 * B;
+}
+static void 
+draw_text_line (DiaRenderer *self, TextLine *text_line,
+		Point *pos, Alignment alignment, Color *color)
+{
+  DiaCairoRenderer *renderer = DIA_CAIRO_RENDERER (self);
+  DiaCairoInteractiveRenderer *interactive = DIA_CAIRO_INTERACTIVE_RENDERER (self);
+
+  if (interactive->highlight_color) {
+    /* the high_light color is just taken as a hint, alternative needs
+     * to have some contrast to cursor color (curently hard coded black)
+     */
+    static Color alternate_color = { 0.5, 0.5, 0.4 };
+    real rl, cr1, cr2;
+
+    /* just draw the box */
+    real h = text_line_get_height (text_line);
+    real w = text_line_get_width (text_line);
+    real x = pos->x;
+    real y = pos->y;
+
+    y -= text_line_get_ascent(text_line);    
+    x -= text_line_get_alignment_adjustment (text_line, alignment);
+
+    rl = calculate_relative_luminance (color) + 0.05;
+    cr1 = calculate_relative_luminance (interactive->highlight_color) + 0.05;
+    cr1 = (cr1 > rl) ? cr1 / rl : rl / cr1;
+    cr2 = calculate_relative_luminance (&alternate_color) + 0.05;
+    cr2 = (cr2 > rl) ? cr2 / rl : rl / cr2;
+
+    /* use color giving the better contrast ratio, if necessary 
+     * http://www.w3.org/TR/2008/REC-WCAG20-20081211/#visual-audio-contrast-contrast
+     */
+    if (cr1 > cr2)
+      cairo_set_source_rgba (renderer->cr, 
+			   interactive->highlight_color->red,
+			   interactive->highlight_color->green,
+			   interactive->highlight_color->blue,
+			   1.0);
+    else
+      cairo_set_source_rgba (renderer->cr, 
+			   alternate_color.red,
+			   alternate_color.green,
+			   alternate_color.blue,
+			   1.0);
+
+    cairo_rectangle (renderer->cr, x, y, w, h);
+    cairo_fill (renderer->cr);
+  }
+  DIA_RENDERER_CLASS (parent_class)->draw_text_line (self, text_line, pos, alignment, color);
+}
+static void
+draw_object_highlighted (DiaRenderer     *self, 
+			 DiaObject       *object,
+			 DiaHighlightType type)
+{
+  DiaCairoInteractiveRenderer *interactive = DIA_CAIRO_INTERACTIVE_RENDERER (self);
+
+  switch (type) {
+  case DIA_HIGHLIGHT_TEXT_EDIT:
+    interactive->highlight_color = &text_edit_color;
+    break;
+  case DIA_HIGHLIGHT_CONNECTIONPOINT_MAIN:
+  case DIA_HIGHLIGHT_CONNECTIONPOINT:
+  case DIA_HIGHLIGHT_NONE:
+    interactive->highlight_color = NULL;
+    break;
+  }
+  /* usually this method would need to draw the object twice,
+   * once with highlight and once without. But due to our
+   * draw_text_line implemntation we only need one run */
+  object->ops->draw(object, self);
+  /* always reset when done with this object */
+  interactive->highlight_color = NULL;
+}
 static void 
 dia_cairo_interactive_renderer_iface_init (DiaInteractiveRendererInterface* iface)
 {
@@ -183,6 +271,7 @@ dia_cairo_interactive_renderer_iface_init (DiaInteractiveRendererInterface* ifac
   iface->fill_pixel_rect = fill_pixel_rect;
   iface->copy_to_window = copy_to_window;
   iface->set_size = set_size;
+  iface->draw_object_highlighted = draw_object_highlighted;
 }
 
 GType
@@ -305,6 +394,8 @@ cairo_interactive_renderer_class_init (DiaCairoInteractiveRendererClass *klass)
 
   /* mostly for cursor placement */
   renderer_class->get_text_width = get_text_width;
+  /* highlight for text editing is special */
+  renderer_class->draw_text_line = draw_text_line;
 }
 
 static void