docs: That Viewtype::Sticker may be changed to Image and how to disable that (#6352)

Author: iequidoo

deltachat-ffi/deltachat.h

@@ -5393,6 +5393,8 @@ int64_t         dc_lot_get_timestamp     (const dc_lot_t* lot);
 
 /**
  * Message containing a sticker, similar to image.
+ * NB: When sending, the message viewtype may be changed to `Image` by some heuristics like checking
+ * for transparent pixels.
  * If possible, the UI should display the image without borders in a transparent way.
  * A click on a sticker will offer to install the sticker set in some future.
  */

deltachat-jsonrpc/src/api/types/message.rs

@@ -273,6 +273,9 @@ pub enum MessageViewtype {
     Gif,
 
     /// Message containing a sticker, similar to image.
+    /// NB: When sending, the message viewtype may be changed to `Image` by some heuristics like
+    /// checking for transparent pixels. Use `Message::force_sticker()` to disable them.
+    ///
     /// If possible, the ui should display the image without borders in a transparent way.
     /// A click on a sticker will offer to install the sticker set in some future.
     Sticker,

src/message.rs

@@ -2094,6 +2094,9 @@ pub enum Viewtype {
     Gif = 21,
 
     /// Message containing a sticker, similar to image.
+    /// NB: When sending, the message viewtype may be changed to `Image` by some heuristics like
+    /// checking for transparent pixels. Use `Message::force_sticker()` to disable them.
+    ///
     /// If possible, the ui should display the image without borders in a transparent way.
     /// A click on a sticker will offer to install the sticker set in some future.
     Sticker = 23,