Summary of Schematic Editor Operations

ISSIE features developed over several years to help you create readable schematics very quickly.

Keys below are given for Windows and Linux. On macOS Ctrl is usually Cmd, and a few chords differ. The authoritative list for your platform is generated from the code: press Info → Keyboard Shortcuts. The same actions are also on the Edit and View menus, and on the right-click menus, each labelled with its key.

Placing and editing components

Feature	How	Explanation
Place a component	Click it in the Catalogue, then click the canvas — or drag it straight from the Catalogue and drop it where you want it	While you drag, a ghost of the real symbol follows the cursor. A drop onto space already occupied by another symbol is refused rather than overlapping them
Component tooltips	Hover any Catalogue entry, or any field label in Properties	Every component explains what it is for, and every field explains what it sets and what people get wrong about it
Find a component	Type in the Catalogue's search box	Matches the explanations as well as the names, so "subtract" finds the N bits XOR. Sections holding a match open themselves
Size-to-fit	`Ctrl-0`	Most often used keyboard shortcut: zooms and centres the schematic so it all fits on screen
Zoom the canvas	`Ctrl`+`+` / `Ctrl`+`-`; `Ctrl`+mouse wheel	`Ctrl` with `+` `-` `0` zooms whatever you are looking at — the schematic, or the waveforms in the wave simulator. Add `Alt` to zoom the whole application instead
Pan the canvas	`Space`+drag or `Shift`+drag (or two-finger scroll)
Rotate and flip components	`Ctrl`+`Right`: rotate clockwise `Ctrl`+`Left`: rotate anti-clockwise `Ctrl`+`Up`: flip vertically `Ctrl`+`Down`: flip horizontally	Also on the Edit menu and on a component's right-click menu
Undo / redo	`Ctrl-Z` / `Ctrl-Y`, or the on-screen buttons
Copy / paste	`Ctrl-C` / `Ctrl-V`, or the on-screen buttons	Duplicates keep the label with an incremented number. Works across sheets
Move a component's label	Drag the label; `Ctrl-Shift-Right` rotates it
Change port location on custom components	Hold `Ctrl` and drag a port to another position on the outline — or use Move ports on the component's right-click menu	Custom components can have a lot of ports; move them to make a readable symbol
Resize a custom component	Hold `Ctrl` and drag a corner, use Resize symbol on its right-click menu, or set `Width Scale` / `Height Scale` in Properties	Auto-sizing keeps port legends from overlapping; override it when you want a particular shape
Change anything about a component	Select it and use the Properties tab	Labels, bus widths, number of gate inputs, MUX input order, optional adder/counter ports, memory contents, Verilog source
Align / distribute	`Ctrl-Shift-A` / `Ctrl-Shift-D`; rotate a label with `Ctrl-Shift-R`	Same-type components in the selection are aligned or evenly spaced; other types are left alone
Rotate or scale a block	Drag a selection rectangle, then use the handles on the selection box	`Shift`-click adds or removes one component from the selection

Wires and connections

Feature	How	Explanation
Auto-routing with fixed segments	Automatic	Issie will nearly always route and separate all schematic connections neatly with no manual routing required. Any wire segment can be manually dragged to a desired position and "fixed", with other segments and wires auto-routed around it
Unfix a wire	Right-click the wire → Unfix Wire	Returns a hand-routed wire to auto-routing
Re-separate / re-route	Edit menu, or Reroute all wires on the canvas right-click menu	Applies the whole-sheet tidy-up to the selection, or to everything
Wire type	`View` → `Wire Type`	`Jump`, `Radiussed` or `Modern` wires. Purely a display choice — it does not change the design
Wire arrows	`View` → `Toggle Wire Arrows`	Show the direction of signals at wire end-points
Net labels	Catalogue → `Input / Output` → `Net Label`	Every net label with the same name is one net, joined without wires. Use for long connections and high fan-out. Exactly one label in a same-name set must be driven
Terminate an unused output	`Not Connected` component, or a `Viewer`	Issie will otherwise report the dangling output — and offer to insert the `Not Connected` for you

Sheets, hierarchy and the project

Feature	How	Explanation
Custom components	Catalogue → `This project`	Any design sheet can be placed in another sheet, any number of times
Design hierarchy tree	The Sheet menu	The whole project drawn as a tree with connector lines, showing which sheet contains which. The same tree appears in the waveform simulator
Sheet right-click menu	Right-click a sheet in that tree	Rename, Duplicate, Delete, Set as top, Save as library component, Write design as Verilog
Add a description to a sheet	De-select everything, open Properties, click `Add Description`	The description appears against the sheet as an ⓘ button, and is shown in Properties wherever the sheet is used as a custom component
Sheet parameters	Properties with nothing selected → `Add Parameter`	Named integer parameters, used in arithmetic expressions for bus widths and constants. Each instance of the sheet supplies its own values. Memory address and word widths are not yet parameterisable. See Parameter System
Component libraries	Catalogue → `Library`	Ready-made parameterised components. Choosing one copies its sheet into your project and asks for its parameter values, so it stays an ordinary editable sheet
Import a sheet	`Sheet` → `Import Sheet`	Copy a sheet in from another project
Project browser	`Project` → `New project` / `Open project`	An in-app file browser: the projects inside a folder are listed and can be opened with the arrow keys and `Enter`
Automatic backups	Automatic	Every sheet is continuously snapshotted into a `backup/` subdirectory of the project

Simulation, appearance and help

Feature	How	Explanation
Step simulation	`Simulations` → `Step Simulation`	Set inputs and read outputs immediately. `Viewer` components expose signals from any subsheet
Truth table for combinational logic	`Simulations` → `Truth Table`	For a full sheet, or for just the components you select. Reduce it with input constraints, hidden columns, redundancy removal, or algebraic inputs
Waveform simulation	`Simulations` → `Wave Simulation`	See Features for what it can do
Add waveforms from the schematic	Right-click a component while a wave simulation is running → Add waveforms to viewer
Read a value off the schematic	Rest the mouse on a wire while either simulator is running	The value that wire carries appears beside the pointer — at the waveform cursor's cycle, or at the step simulator's current clock tick — in that simulator's radix. Nothing is shown for a wire on a sheet the simulation holds more than one copy of, since there would be no single answer
Themes	`View` → `Theme`	`Grayscale`, `Light` or `Colourful`
Grid	`View` → `Toggle grid`
Right-click context menus	Right-click a component, a custom component, a wire, the canvas, a sheet in the tree, or the project path	Each offers exactly the actions that apply there, labelled with their shortcuts
Keyboard shortcuts	Info → Keyboard Shortcuts	Generated from the same table the app dispatches keys with, for your platform, so it is always correct
Errors	Automatic	Every error names what is wrong and how to correct it, highlights the components and connections responsible on the canvas, and where the fix is unambiguous offers a button that applies it and restarts the simulation

Details of wire routing and symbol alignment

Snapping

This allows symbol edges to stick to other symbol edges when moving them in ISSIE, or symbols to stick to positions that make wires straight.

Explicit arrangement

Selections of same-type components can be aligned vertically or horizontally, or distributed with equal spacing. Differing type components are omitted from the operation even if selected.

Manual wire routing

Manual routing has been reworked to have the following behaviour:

A non-binding segment can be dragged anywhere
A binding segment cannot be dragged past the nubLength of the wire, which is the minimum length of the nubs coming out of the ports (defined as static member nubLength in Wire type)

A segment is defined as binding for a particular port if it is the first segment of non-zero length perpendicular to the port's nub.

Wire auto-routing

Auto-routing is done in 5 stages:

Normalise the routing problem so that the output port is facing right
Generate the initial segment list
Rotate the problem back to it's in the original orientation
Run an iterative autorouting algorithm that attempts to create a valid route not overlapping any symbol by moving initial segments.
Run a whole-sheet segment separation algorithm that spreads wires out evenly.

Segments are generated based off of the two ports for each wire, with the assumption that the output port is always facing right. The orientation of the input port is checked as well as its relative position to the output port, allowing us to generate an initial segment list. This segment list consists of a small “nub” segment immediately joining the input and output port. These are followed by 0 length segments in order to facilitate previous functionality of ISSIE where we could drag wires fully. After these 0 length segments we create the remaining segments to link the two ports. These distances are either set to halfway between the two ports, or a small distance in order to get past the boundaries of a symbol.

Details of Operations

Copy and paste

The on-screen copy & paste buttons can duplicate single components, or selected sets of components (see selection below). They can also be used to copy components from one design sheet to a new one.

Canvas zooming

The canvas can be zoomed in or out with Ctrl++ and Ctrl+-, or auto-zoomed and panned to fit the whole circuit with Ctrl-0. The same chords work on macOS with Cmd. Adding Alt to any of the three zooms the whole application rather than the schematic.

Symbol rotation

Individual symbols can be rotated or flipped using the right-click menu or the Issie edit menu.

Wire display types

Wires can be displayed as radial, modern, or old-style jump. Switching display types can be done at any time and does not change the schematic.

Radial wires are the most interesting (and readable) form of wire display. Wire bends have small quadrant connections thus distinguishing between wires that cross and a wire joining two perpendicular wires. Visually, radial display makes connectivity easier to follow. The default radius for the wire quadrants is defined as static member radius = 5.0 in Wire type. However, for very small wires, this radius is changed to prevent visual bugs. When drawing radii, the length of the smallest segment the curve connects to is checked, and if its length is <5, the radius is shrunk to match it. Due to the limitations of drawing Arcs in SVG, these radii can only be integer valued, leading to small inconsistencies when a segment is a small non integer value (i.e. 1.5).

Symbol auto-sizing

Custom components (symbols) are dynamically resized depending on their port configuration. The minimum distance between 2 ports is set as GridSize = 30, which is defined as a [<Literal>] at the top of Symbol.fs. The dimensions of a component are determined as follows:

Height: Determined purely from the maximum number of ports on the left or right edge (n), setting the height to (n+1)GridSize, and spreading the ports GridSize apart.
Width: The distance between ports is determined by the maximum between the largest port label and GridSize. This ensures that the labels of the ports cannot overlap, whilst still being a minimum distance apart. The width can be calculated for both the Top and Bottom edges using the same approach as above using the maximum value, and taking the largest of these 2 values. In addition, the length of the longest labels from the Left and Right sides, as well as the component label (displayed in the center of the component) are added up and compared to the width obtained from the previous calculation. By selecting the component width as the maximum of these values, it can be ensured that labels associated with the component / ports do not overlap.

Custom components' ports can be placed to different edges on the Symbol by pressing Ctrl (Cmd) and dragging the port. When a port is dragged onto a different edge, the width and height of the component is automatically resized. The ports on one edge are always equidistant. The height of the component is determined purely from the number of ports on the left or right edge, depending on which one has more ports. The width of the component also considers the lengths of the ports on the top and bottom edges. The distance between ports on the top and bottom edges is big enough, such that it can fit the longest portlabel on the edge, but never smaller than 1 gridsize. The necessary width of the top/bottom edge is determined from this distance and from the number of ports on this edge. The width of the component is given by either the top or bottom edge width, whichever is bigger.

The same UI (dragging component corners) can be used manually to override auto-sizing and make the custom symbol a desired size.

Port placement

The ordering of the ports on a custom symbol is represented by its index in the list associated to a particular edge of the Symbol (Top, Left, Bottom, Right). We allow ports to be moved for custom components by clicking and dragging the port while holding down the Ctrl key.

Schematic rotation and scaling

Any group of components on the schematic can be selected, and then rotated and/or scaled.

Dragging the mouse will select a rectangle.
Shift-click will add or remove a component from the current selection.
A selected block of components will show icons for intuitive rotating and scaling.