can we have different color for the symbol outline from the scene background color? Now it is unclear in the rendering output what is still part of the billboard and what is already the background...

probably we don't need this #include of XML utils here anymore

probably we don't need this #include of XML utils here anymore

The comment should say that the ownership of the symbol object is transferred

Do we still need this constructor? If not better to remove it

Ummm.... this can be simplified - the returned symbolElem could be simply attached to DOM (without saving the XML to a text stream).

answer to Nyall's question is yes - it does take ownership if the image does not have a parent yet - it would be good to have a comment here that the image gets parented to texture2D so it is clear...

no memory leak here anymore :)

"dots per inch"

It is worth noting that the 'selected' parameter was added in 3.10

there should be no need to set unit scale and no rotation to the matrix - that should be the default already.

is there any reason for this line? maybe some leftover from debugging?

use "context" that is passed to readXml() method instead of creating an empty context - otherwise relative paths would not get resolved correctly to absolute paths

this code should use QgsSymbolLayerUtils::saveSymbol() - and the current read/write context should be passed to it so that any paths can be converted to relative.

we can make this method private - I guess client code should use the higher level calls (setTexture2DFrom...()) or actually its body could be moved to setTexture2DFromTextureImage() as that's the only place where it's used and it's single line only...

Is this method used anywhere? if not we can remove it...

```suggestion * \param set to TRUE to render the symbol in a selected state ```

Possible ownership issue here, depending on whether or not setBillboardSymbol takes ownership or internally makes a clone. (Ideally it should take ownership and follow the patterns from other parts of QGIS). In which case, this should use QgsSymbolButton::clonedSymbol instead.

remove

Does this take ownership?

This is leaked -- create it on the stack, not the heap

const?

Does this take ownership?

copy-paste error

wrong header (copy-paste error)

please remove commented out code

please remove commented out code