Martino Ferrari
f238e717b2
A review of the whole node editor. The hit test measured the distance to the 24 curve samples rather than to the segments between them, so a wire spanning several rows was unpickable between two samples -- the probe now places its boxes 280 units apart and prints the nearest sample's own 8.4 against a 3.0 tolerance, which the point test would have missed. A refused connection said nothing: the message is now carried in `MathDialog::refusal` and shown once by the single writer of the label, and a self-wire is refused through the real drag-end path instead of only through `math_connect()`. Two defects were found only by the new assertions. `math_dialog_sync()` re-entered itself -- `gtk_drop_down_set_selected()` emits `notify::selected` for a programmatic set too, and the handler answers by syncing again, which consumed the refusal before it could be drawn -- so the body is now guarded one level deep. And a deleted node left `selected_wire` naming an index that afterwards belongs to a different wire, so `Delete` cleared an input on the wrong node. A node is placed in the first free grid cell rather than at the end of the list's own cell, so a node added after a delete no longer lands on top of a survivor; the label ellipsizes with a tooltip rather than wrapping, because a wrapped line makes the dialog's height depend on the text in it.
62 lines
3.9 KiB
Plaintext
62 lines
3.9 KiB
Plaintext
<b>Math channels</b>
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A math channel is a signal computed from other signals. You build it as a small graph — source
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nodes, operations, one output — and udpscope then treats the result as an ordinary channel.
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<b>How to reach it</b>
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The math button in the toolbar, or <tt>g</tt>. The pane's <tt>+</tt> adds a channel, and opening
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one shows the graph editor: nodes as boxes, click a box to select it and edit its parameters beside
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the canvas. Inside the editor, <i>add node</i> is a menu button whose popover picks the op, so the
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node arrives as the operation you asked for.
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<b>Graph gestures:</b> <b>drag</b> from an output port to an input port to wire them; drag a
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wired input port off its connection to detach it; click a wire and press <tt>Delete</tt> to remove
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it; drag a box to move it. <b>Wheel</b> zooms about the pointer. <b>Drag the background</b> to
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pan. <tt>f</tt> fits all nodes into view; <tt>Ctrl+0</tt> resets the view. <i>tidy</i>, the button
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beside <i>fit</i> in the editor, lays the graph out in topological columns and frames it. The orange
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dot marks the output node; click <i>set as output</i> to move it.
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<b>Worth knowing</b>
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• The graph is evaluated as an ordered list, so a node may only read ones <i>above</i> it. A
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wire drawn right to left re-sorts the list silently so the graph stays valid. A cycle is
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unrepresentable: the connection is refused rather than created, and the line beneath the form
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says why — a loop, or a node asked to read itself.
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• A derived channel <i>is</i> a channel. It appears in the signal panel, can be plotted,
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measured, exported, and used as a source for another math channel.
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• The math runs on the <b>stored</b> samples — decimated and averaged — so a cutoff you type in
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Hz means the rate the filter will actually run at. Change the window across a decimation
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boundary and the coefficients are rebuilt for the new rate.
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• A source may only name an <i>acquired</i> channel. The stream's timestamp signal is not one:
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a graph sourced from it validates and then reads NaN for ever, so the dropdown does not
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offer it.
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• The output defaults to the <i>last</i> node, and a node added to a linear graph becomes the
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output. Choosing an earlier node explicitly is respected.
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• Every numeric field starts at its own identity value — gain 1, offset 0 — not at the bottom
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of its range.
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<b>Example</b>
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<tt>[sine] → [gain x2]</tt> gives a channel reading <tt>y=[-2, 2]</tt>. A 100 Hz low pass on the
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same source passes 50 Hz at 0.97 and 2 kHz at 0.002; a 1 kHz band pass with Q=2 passes 200 Hz at
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0.05, 1 kHz at 0.95 and 4 kHz at 0.05. Each derived channel must hold exactly as many samples as
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the shared clock has time slots.
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<b>Why an operation sometimes does nothing</b>. A graph's <i>output</i> is the node whose value
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becomes the channel, and it is drawn as the orange dot. A new graph is built source, then operation,
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and the last node added becomes the output -- but a graph whose output is left on the source is
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valid and simply passes its input through, which is the usual reason a gain or a filter appears to
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have no effect. <i>Set as output</i> moves the dot.
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<b>Apply is insensitive while the graph is incomplete.</b> A line beneath the form says why:
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an input that is not connected, no output chosen, or a <i>channel</i> node naming a signal the
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scope is not acquiring. Only the channels being acquired are offered, because a source that is not
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acquired reads as no data for ever — and a graph that reads NaN is harder to diagnose than one that
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would not save.
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<b>The filters are real filters.</b> A math channel's samples are produced as the stream arrives,
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once per stored slot, so a low pass carries the history a filter needs. A cutoff typed in hertz is
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against the <i>stored</i> rate, which is the wire rate until a wide window makes the buffer decimate
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-- the status line's rate is that number, and the filters are rebuilt whenever it changes.
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