Program custom condition
You should use hook “wdp_conditions” to append new condition + load new PHP class and html template.
You should use one plugin to add many custom conditions.
Please, review simple addon.
For example, we have custom product field “area” (different for each product).
Sample addon embeds new condition to section “Cart Conditions”.
Template custom-template-area-size.php describes supported operations and input for comparable value.
The addon uses method check (class WDP_Custom_Condition_Area_Size) to get total area and compare with defined value.