buttonImGuiMouseButton index: 0 left, 1 right, 2 middle.
True if the mouse button is currently held down; false otherwise.
To refer to a mouse button, you may use named enums in your code e.g. ImGuiMouseButton.Left, ImGuiMouseButton.Right.
You can also use regular integer: it is forever guaranteed that 0=Left, 1=Right, 2=Middle.
Dragging is reported only after the mouse moves far enough from the initial click (see lock_threshold and io.MouseDragThreshold, where io is the field view returned by ImGui.viewImGuiIO(ioHandle)).
is mouse button held?
Test whether a mouse button is held down.