get chat and contact colors

src/dc_chat.c

@@ -259,6 +259,46 @@ cleanup:
 }
 
 
+/**
+ * Get a color for the chat.
+ * For 1:1 chats, the color is calculated from the contact's email address.
+ * Otherwise, the chat name is used.
+ * The color can be used for an fallback avatar with white initials
+ * as well as for headlines in bubbles of group chats.
+ *
+ * @memberof dc_chat_t
+ * @param chat The chat object.
+ * @return Color as 0x00rrggbb with rr=red, gg=green, bb=blue
+ *     each in the range 0-255.
+ */
+uint32_t dc_chat_get_color(const dc_chat_t* chat)
+{
+	uint32_t      color = 0;
+	dc_array_t*   contacts = NULL;
+	dc_contact_t* contact = NULL;
+
+	if (chat==NULL || chat->magic!=DC_CHAT_MAGIC) {
+		goto cleanup;
+	}
+
+	if(chat->type==DC_CHAT_TYPE_SINGLE) {
+		contacts = dc_get_chat_contacts(chat->context, chat->id);
+		if (contacts->count >= 1) {
+			contact = dc_get_contact(chat->context, contacts->array[0]);
+			color = dc_str_to_color(contact->addr);
+		}
+	}
+	else {
+		color = dc_str_to_color(chat->name);
+	}
+
+cleanup:
+	dc_array_unref(contacts);
+	dc_contact_unref(contact);
+	return color;
+}
+
+
 /**
  * Get archived state.
  *

src/dc_contact.c

@@ -217,7 +217,7 @@ char* dc_contact_get_first_name(const dc_contact_t* contact)
  * using dc_set_config(context, "selfavatar", image).
  *
  * @memberof dc_contact_t
- * @param chat The contact object.
+ * @param contact The contact object.
  * @return Path and file if the profile image, if any.
  *     NULL otherwise.
  *     Must be free()'d after usage.
@@ -245,6 +245,27 @@ cleanup:
 }
 
 
+/**
+ * Get a color for the contact.
+ * The color is calculated from the contact's email address
+ * and can be used for an fallback avatar with white initials
+ * as well as for headlines in bubbles of group chats.
+ *
+ * @memberof dc_contact_t
+ * @param chat The contact object.
+ * @return Color as 0x00rrggbb with rr=red, gg=green, bb=blue
+ *     each in the range 0-255.
+ */
+uint32_t dc_contact_get_color(const dc_contact_t* contact)
+{
+	if (contact==NULL || contact->magic!=DC_CONTACT_MAGIC) {
+		return 0x000000;
+	}
+
+	return dc_str_to_color(contact->addr);
+}
+
+
 /**
  * Check if a contact is blocked.
  *

src/dc_tools.c

@@ -604,6 +604,32 @@ clist* dc_str_to_clist(const char* str, const char* delimiter)
 }
 
 
+int dc_str_to_color(const char* str)
+{
+	static uint32_t colors[] = {
+		0xe56555,
+		0xf28c48,
+		0x8e85ee,
+		0x76c84d,
+		0x5bb6cc,
+		0x549cdd,
+		0xd25c99,
+		0xb37800
+	};
+
+	int checksum = 0;
+	int str_len = strlen(str);
+	for (int i = 0; i < str_len; i++) {
+		checksum += (i+1)*str[i];
+		checksum %= 0x00FFFFFF;
+	}
+
+	int color_index = checksum % (sizeof(colors)/sizeof(uint32_t));
+
+	return colors[color_index];
+}
+
+
 /*******************************************************************************
  * clist tools
  ******************************************************************************/

src/dc_tools.h

@@ -44,6 +44,7 @@ void    dc_free_splitted_lines     (carray* lines);
 char*   dc_insert_breaks           (const char*, int break_every, const char* break_chars); /* insert a break every n characters, the return must be free()'d */
 char*   dc_str_from_clist          (const clist*, const char* delimiter);
 clist*  dc_str_to_clist            (const char*, const char* delimiter);
+int     dc_str_to_color            (const char*);
 
 // from libetpan/src/data-types/base64.h (which cannot be included without adding libetpan/src/... to the include-search-paths, which would result in double-file-name-errors, so, for now, we use this hack)
 char*   encode_base64              (const char * in, int len);

src/deltachat.h

@@ -464,6 +464,7 @@ int             dc_chat_get_type             (const dc_chat_t*);
 char*           dc_chat_get_name             (const dc_chat_t*);
 char*           dc_chat_get_subtitle         (const dc_chat_t*);
 char*           dc_chat_get_profile_image    (const dc_chat_t*);
+uint32_t        dc_chat_get_color            (const dc_chat_t*);
 int             dc_chat_get_archived         (const dc_chat_t*);
 int             dc_chat_is_unpromoted        (const dc_chat_t*);
 int             dc_chat_is_self_talk         (const dc_chat_t*);
@@ -571,6 +572,7 @@ char*           dc_contact_get_display_name  (const dc_contact_t*);
 char*           dc_contact_get_name_n_addr   (const dc_contact_t*);
 char*           dc_contact_get_first_name    (const dc_contact_t*);
 char*           dc_contact_get_profile_image (const dc_contact_t*);
+uint32_t        dc_contact_get_color         (const dc_contact_t*);
 int             dc_contact_is_blocked        (const dc_contact_t*);
 int             dc_contact_is_verified       (dc_contact_t*);