Programming continued... vol 3

Long time ago I crossed my limits of understanding in programming, but still, through luck and nice findings I still keep fiddling with my little project. During last week I have come from Qt's "Elastic nodes" example to something that almost looks like a functional prototype.

Biggest improvements are:

• major UI overhaul from node-editor to multiple dockable areas that contain DAG view, table view and node properties
• knob callbacks work! With some pure luck I managed to get the callback thing working
• knobs can be added to Op with only one line of code in Op::knobs method
• new Ops: simple sort (column and direction) and SQL queries
• nodes can be attached to existing edges by dragging
• keyboard shortcut to connect viewer to selected node
• properties view shows knobs for added nodes. Node parameters subwindow can be closed and opened again by double-clicking the node and last opened is positioned on top. 

UI is now based on dockable widgets so that layout can be changed. Look is customised with stylesheet file.

Knob callbacks work nicely, the idea how it should work came one morning and I quickly scribbled some code on a piece of paper. It worked without zero modifications! Adding knobs is very similar to how it works with Nuke plugin development. Syntax is like: "String_knob(callback, &value, label);" where callback is a knob_callback pointer, value is Op variable that is associated with knob, and label is knob label. Knobs get added into row layout that takes care of label and knob placement. In addition I created functions (Nuke style again) to modify last added knob. For example ADD_VALUES(callback, "Ascending, Descending"); adds value list to last knob (ComboBox or similar). Knobs show tooltips and whole node subwindow shows help info when you click on ? button :)

SQL queries took some fiddling with my datamodel because at the moment it is built on QStandardItemModel. To make queries I have to push items into sql database (QSQLITE internally), make the query, and then put items back to model. All Select commands work great but for some reason I can't get queries that modify table structure or delete row to work. They execute when they are hardwired into code but through UI these queries just don't work.

Node area got some love also, because I was annoyed by dragging every connection manually. So now nodes can be inserted into existing edges. One thing is yet to do with node editor - ability to resize backdrops. At the moment they show the resizing dot in the corner but resizing is not working.