text: Add delete_surrounding_text to protocol

Add delete_surrounding_text event in the text_model interface and the
request in the input_method_context interface. Implement it in the
example editor client and in the example keyboard so that the backspace
key works with it.

Signed-off-by: Jan Arne Petersen <jpetersen@openismus.com>

clients/editor.c

@@ -212,6 +212,8 @@ static void text_entry_insert_at_cursor(struct text_entry *entry, const char *te
 static void text_entry_set_preedit(struct text_entry *entry,
 				   const char *preedit_text,
 				   int preedit_cursor);
+static void text_entry_delete_text(struct text_entry *entry,
+				   uint32_t index, uint32_t length);
 
 static void
 text_model_commit_string(void *data,
@@ -249,6 +251,31 @@ text_model_preedit_string(void *data,
 	widget_schedule_redraw(entry->widget);
 }
 
+static void
+text_model_delete_surrounding_text(void *data,
+				   struct text_model *text_model,
+				   int32_t index,
+				   uint32_t length)
+{
+	struct text_entry *entry = data;
+	uint32_t cursor_index = index + entry->cursor;
+
+	if (cursor_index > strlen(entry->text)) {
+		fprintf(stderr, "Invalid cursor index %d\n", index);
+		return;
+	}
+
+	if (cursor_index + length > strlen(entry->text)) {
+		fprintf(stderr, "Invalid length %d\n", length);
+		return;
+	}
+
+	if (length == 0)
+		return;
+
+	text_entry_delete_text(entry, cursor_index, length);
+}
+
 static void
 text_model_preedit_styling(void *data,
 			   struct text_model *text_model)
@@ -304,6 +331,7 @@ text_model_deactivated(void *data,
 static const struct text_model_listener text_model_listener = {
 	text_model_commit_string,
 	text_model_preedit_string,
+	text_model_delete_surrounding_text,
 	text_model_preedit_styling,
 	text_model_key,
 	text_model_selection_replacement,
@@ -515,6 +543,21 @@ text_entry_set_anchor_position(struct text_entry *entry,
 	widget_schedule_redraw(entry->widget);
 }
 
+static void
+text_entry_delete_text(struct text_entry *entry,
+		       uint32_t index, uint32_t length)
+{
+	if (entry->cursor > index)
+		entry->cursor -= length;
+
+	entry->text[index] = '\0';
+	strcat(entry->text, entry->text + index + length);
+
+	text_entry_update_layout(entry);
+
+	widget_schedule_redraw(entry->widget);
+}
+
 static void
 text_entry_draw_selection(struct text_entry *entry, cairo_t *cr)
 {

clients/keyboard.c

@@ -222,6 +222,10 @@ keyboard_handle_key(struct keyboard *keyboard, const struct key *key)
 							    strlen(keyboard->keyboard->preedit_string));
 			break;
 		case keytype_backspace:
+			if (strlen(keyboard->keyboard->preedit_string) == 0) {
+				input_method_context_delete_surrounding_text(keyboard->keyboard->context,
+									     -1, 1);
+			}
 			break;
 		case keytype_enter:
 			break;