This is why it is important to be able to use background= instead of getElementById('board0').style.backgroundImage= in the JavaScript for a button. Since I would prefer to use my own buttons for better control of the layout, I'm hoping you can update Display() to change the background image to whatever the value of background is.
I don't think using Display would bring any solace: it would also not know what Diagram your hand-made buttons belong to. It would do the replacement in the currently active Diagram on the page, which might not at all be the Diagram you intended it to work for. If you want to get the same results as when Display() would do the replacement, you can write
The variable 'active' keeps the number of the Diagram that last received a mouse click. (Or any other activity, such as opening the AI panel.) Each clickable element in a Diagram knows the number of the Diagram it belongs to, and passes that to the click handler. If this is not the Diagram indicated by 'active', the routine SwitchDiag() is called to re-initialize the clicked Diagram before handling the click, and this becomes the new active Diagram. Display() uses this 'active' variable to address the squares it has to change, and would also use it to decide which background to alter.
The problem is that the Diagram numbers are dynamically generated during Initialization, on loading the page. The initialization routine collects all HTML element with class="idiagram", through getElementsByClassName('idiagram'). This delivers an array with the HTML elements as objects in it, in the order the Diagrams appear on the page. And the index in that array will be the Diagram number. When it then realizes the Diagrams one by one it uses this number in the id attribute of all Diagram elements, and as argument in the calls to event handlers attached to these elements. But as new Diagrams appear on the page, the numbers will change. So it is not possible to refer to the Diagrams through a hardcoded number in a button.
In principle the satellite parameter was introduced to associate external elements with a given Diagram. But that only works for elements that the Diagram initializator actively searches on the page (such as piece lists).
The only solution I can think of is to somehow 'broadcast' the Diagram numbers in a global associative array, indexed by the satellite value. That could be used to write things like
I don't think using Display would bring any solace: it would also not know what Diagram your hand-made buttons belong to. It would do the replacement in the currently active Diagram on the page, which might not at all be the Diagram you intended it to work for. If you want to get the same results as when Display() would do the replacement, you can write
getElementById('board' + active).style.backgroundImage=...The variable 'active' keeps the number of the Diagram that last received a mouse click. (Or any other activity, such as opening the AI panel.) Each clickable element in a Diagram knows the number of the Diagram it belongs to, and passes that to the click handler. If this is not the Diagram indicated by 'active', the routine SwitchDiag() is called to re-initialize the clicked Diagram before handling the click, and this becomes the new active Diagram. Display() uses this 'active' variable to address the squares it has to change, and would also use it to decide which background to alter.
The problem is that the Diagram numbers are dynamically generated during Initialization, on loading the page. The initialization routine collects all HTML element with class="idiagram", through getElementsByClassName('idiagram'). This delivers an array with the HTML elements as objects in it, in the order the Diagrams appear on the page. And the index in that array will be the Diagram number. When it then realizes the Diagrams one by one it uses this number in the id attribute of all Diagram elements, and as argument in the calls to event handlers attached to these elements. But as new Diagrams appear on the page, the numbers will change. So it is not possible to refer to the Diagrams through a hardcoded number in a button.
In principle the satellite parameter was introduced to associate external elements with a given Diagram. But that only works for elements that the Diagram initializator actively searches on the page (such as piece lists).
The only solution I can think of is to somehow 'broadcast' the Diagram numbers in a global associative array, indexed by the satellite value. That could be used to write things like
getElementById('board' + sats['xiangqiMainDiagram']).style.backgroundImage=...to make sure that you will always opperate on the Diagram with satellite=xiangqiMainDiagram in its specifications.