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Purpose

Canvas displays are the paradigm for pixel art that happens to show live data. Process diagrams, P&IDs, equipment layouts, architectural overviews. Every element has an explicit Left / Top / Width / Height and you compose by placement, layering, and grouping.

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Prerequisite: load Skill Display Construction — Basics first. It covers theme-first thinking, write mechanics, the build loop, binding gotchassyntax, and spacing/typography tokens.

Section 1 — Canvas mental model

Think in zones, not elements

The worst Canvas displays are built element-first — you place a Rectangle, then another, then wonder why nothing aligns. The good ones are built zone-first.

1. Divide the canvas into zones. Rectangular regions for each process section (Intake, Treatment, Distribution) or each info panel (Equipment Detail, Live Metrics, Ontology Identity).
2. Lay zone background Rectangles first. These are the visual scaffolding — operators read the display by scanning zones, not individual shapes.
3. Place elements WITHIN zone coordinates. Everything in a zone has its Left/Top relative to the zone's origin.
4. Connect zones with flow indicators. Arrows, pipe lines, direction markers.

Canvas sizes

Zone math (any canvas size, N zones)

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margin   = 20
gap      = 15
titleBar = 60          // top strip for display title + status
bottomPanel = 140      // for trend/alarm/summary
zoneHeight = Height - titleBar - bottomPanel - margin
zoneWidth  = (Width - 2*margin - (N-1)*gap) / N
zone[i].Left  = margin + i * (zoneWidth + gap)
zone[i].Top   = titleBar
zone[i].Width = zoneWidth
zone[i].Height = zoneHeight

For a 1600×900 canvas with 3 zones: each zone is ~515 wide × 640 tall. For 4 zones: ~381 wide. For 2 zones: ~780 wide.

Z-order by Elements array order

Canvas has no z-index property. The order of the Elements array IS the z-order — earlier elements render behind, later elements in front. Always place:

1. Full-canvas background Rectangle first (if overriding root Background)
2. Zone background Rectangles next
3. Zone-internal shapes and symbols
4. Labels and text (on top of their containing zones)
5. Interactive overlays (click-zones, hover highlights) last

Section 2 — Shapes (the 7 primitives)

All Canvas-only. All theme-aware (Fill/FillTheme, Stroke/StrokeTheme, StrokeThickness).

Pipe segment pattern

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{
  "Type": "Gridline",
  "Left": 300, "Top": 200,
  "Points": "0,0 100,0 100,60 200,60",
  "StrokeTheme": "Water",
  "StrokeThickness": 6,
  "StrokeLineJoin": "Round",
  "StrokeLineCap": "Round"
}

Then a direction arrow (Polygon, no stretch):

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{
  "Type": "Polygon",
  "Left": 490, "Top": 253,
  "Width": 20, "Height": 14,
  "Points": "0,0 20,7 0,14",
  "Stretch": "None",
  "FillTheme": "Water"
}

Reactor coil overlay (Path)

Zigzag heat-exchange coils over a reactor body:

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{
  "Type": "Path",
  "Left": 305, "Top": 220,
  "Width": 130, "Height": 240,
  "Data": "M0,0 Q65,20 130,0 M0,40 Q65,60 130,40 M0,80 Q65,100 130,80",
  "StrokeTheme": "StateRed",
  "StrokeThickness": 2,
  "Fill": "#00000000",
  "FillTheme": ""
}

Note the stroked-but-unfilled pattern: Fill: "#00000000" + FillTheme: "" gives a transparent fill so the stroke shows without a filled shape underneath.

Section 3 — First-class auto-shapes

These are first-class shape primitives that write with just Type + geometry + colors. The platform auto-injects the underlying Path/Polygon geometry on save. Massive productivity win over composing from primitives.

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{ "Type": "Cylinder", "Left": 300, "Top": 200, "Width": 80, "Height": 180, "FillTheme": "ElementBlue" }

That's an entire vessel. No Points, no Data, no compositing.

Writer normalization — read-back shows expanded form

When you read a display back after writing a Cylinder, you'll see a Path with auto-generated Data. This is expected — the shortcut is a write-time macro. For edits, either add new Cylinders (which normalize the same way) or edit the Path directly.

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Runtime discovery over hardcoded lists

list_elements() also reports Triangle, Octagon, Parallelogram, Hill, Curve, Senoid, Wave, T-Junction under the Control category. Do NOT use these. They're schema phantoms — neither Type: "X" alone nor Type: "X" + SymbolName: "Wizard/X" works. For a triangle, use Polygon with three Points. For a "T-junction" on a pipe, use two Gridlines is the authoritative runtime catalog. Any shape entry not returned by list_elements() in the current release should be treated as non-existent. For shapes beyond the standard set (e.g., triangle, octagon, custom forms), compose from primitives: Polygon with explicit Points handles most custom 2D shapes, and Path handles curves.

Section 4 — Containers (ShapeGroup, SvgGroup, Group)

ShapeGroup — compose equipment with unified state

The killer feature: a FillColorDynamic on the ShapeGroup changes the fill of ALL children at once. Build a vessel from primitives, and the entire vessel can turn red on alarm:

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{
  "Type": "ShapeGroup",
  "Left": 300, "Top": 200,
  "Width": 180, "Height": 220,
  "Stretch": "None",
  "Children": [
    { "Type": "Ellipse",   "Left": 40, "Top": 0,   "Width": 100, "Height": 20 },
    { "Type": "Rectangle", "Left": 40, "Top": 10,  "Width": 100, "Height": 180 },
    { "Type": "Ellipse",   "Left": 40, "Top": 180, "Width": 100, "Height": 20 }
  ],
  "FillTheme": "ElementBlue",
  "Dynamics": [
    {
      "Type": "FillColorDynamic",
      "LinkedValue": "@Tag.Reactor/Alarm",
      "ChangeColorItems": [
        { "Type": "ChangeColorItem", "ChangeLimit": 0, "LimitColor": "#FF1E3A8A" },
        { "Type": "ChangeColorItem", "ChangeLimit": 1, "LimitColor": "#FFEF4444" }
      ]
    }
  ]
}

SvgGroup — when you'd rather author in SVG

Any inline SVG string becomes a ShapeGroup with native WPF shapes:

...

:

{
  "Type": "SvgGroup",
  "Left": 224, "Top": 240,
  "Width": 180, "Height": 220,
  "SvgContent": "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 180 220'><ellipse cx='90' cy='14' rx='60' ry='10' fill='#95a5a6'/><rect x='30' y='14' width='120' height='180' fill='#3498db'/><ellipse cx='90' cy='194' rx='60' ry='10' fill='#95a5a6'/></svg>",
  "Name": "ReactorVessel"
}

Supported SVG elements: rect, circle, ellipse, line, path, polyline, polygon, g.
Supported attributes: fill, stroke, stroke-width, transform, style, class, opacity, rx, ry.
Supported transforms: translate(), scale(), rotate(), matrix().
Avoid: gradients, filters, clip-paths, text, embedded images.

Trade-off: SvgContent hex colors are opaque to the theme system. Fine for process-meaning colors (heat red, water blue), wrong for UI chrome. If you need theme-reactive composed equipment, use ShapeGroup directly.

Group — for interactive panels

Use Group when children need INDEPENDENT dynamics:

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{
  "Type": "Group",
  "Left": 100, "Top": 100,
  "Width": 400, "Height": 280,
  "Children": [
    { "Type": "Rectangle", "Left": 0, "Top": 0, "Width": 400, "Height": 280, "FillTheme": "PanelBackground" },
    { "Type": "TextBlock", "Left": 16, "Top": 16, "Width": 360, "Height": 24, "LinkedValue": "Reactor Control" },
    { "Type": "Button",    "Left": 16, "Top": 220, "Width": 120, "Height": 40, "LabelLink": "Start",
      "Dynamics": [{ "Type": "ActionDynamic", "MouseLeftButtonDown": { "Type": "DynamicActionInfo", "ActionType": "SetValue", "ObjectLink": "@Tag.Reactor/Running", "ObjectValueLink": 1 }}] }
  ]
}

Section 5 — The equipment cookbook

Recipe 1 — Vessel with jacket

The archetype: a cylindrical vessel with a heating jacket that changes color when the heater is running.

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{ "Type": "Ellipse",   "Left": 300, "Top": 180, "Width": 96, "Height": 24, "FillTheme": "ElementGray" },
{ "Type": "Rectangle", "Left": 328, "Top": 150, "Width": 40, "Height": 36, "FillTheme": "ElementGray" },
{ "Type": "Cylinder",  "Left": 276, "Top": 200, "Width": 144, "Height": 300, "FillTheme": "ElementBlue" },
{ "Type": "Rectangle", "Left": 256, "Top": 280, "Width": 22, "Height": 180, "FillTheme": "OffFill",
  "Dynamics": [
    { "Type": "FillColorDynamic", "LinkedValue": "@Tag.Reactor/Heater/Running",
      "ChangeColorItems": [
        { "Type": "ChangeColorItem", "ChangeLimit": 0, "LimitColor": "#FF7F1D1D" },
        { "Type": "ChangeColorItem", "ChangeLimit": 1, "LimitColor": "#FFEF4444" }
      ] }
  ] },
{ "Type": "Rectangle", "Left": 418, "Top": 280, "Width": 22, "Height": 180, "FillTheme": "OffFill",
  "Dynamics": [ /* same FillColorDynamic */ ] }

Elements top to bottom: drive cap (Ellipse), motor housing (Rectangle), vessel body (Cylinder with ElementBlue), left jacket rail (Rectangle with heater-gated FillColorDynamic), right jacket rail (same).

For an impeller shaft: add a thin vertical Rectangle, apply RotateDynamic gated by Running:

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{ "Type": "Rectangle", "Left": 344, "Top": 230, "Width": 8, "Height": 240, "FillTheme": "DefaultStroke",
  "Dynamics": [
    { "Type": "RotateDynamic", "LinkedValue": "30", "IsRpm": true, "OnOffLink": "@Tag.Reactor/Agitator/Running" }
  ] }

LinkedValue: "30" and IsRpm: true means "rotate at 30 rpm." OnOffLink gates the rotation — the shaft only spins when Running=1.

Recipe 2 — Centrifugal pump (Wizard symbol with live dynamics)

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{
  "Type": "Symbol",
  "SymbolName": "Wizard/PUMP",
  "Left": 500, "Top": 300,
  "Width": 80, "Height": 80,
  "SymbolLabels": [
    { "Type": "SymbolLabel", "Key": "State", "LabelName": "State", "LabelValue": "@Tag.Pump1/Running",  "FieldType": "Expression" },
    { "Type": "SymbolLabel", "Key": "RPM",   "LabelName": "RPM",   "LabelValue": "@Tag.Pump1/Speed",    "FieldType": "Expression" }
  ]
}

The symbol itself knows how to change its fill based on State — no extra dynamics needed.

To add a click-to-open-detail action, add the dynamic directly on the Symbol:

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"Dynamics": [
  { "Type": "ActionDynamic",
    "MouseLeftButtonDown": { "Type": "DynamicActionInfo", "ActionType": "OpenDisplay", "ObjectLink": "PumpDetail" } }
]

Recipe 3 — Pipe segment with flow direction

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{ "Type": "Gridline", "Left": 200, "Top": 400, "Width": 300, "Height": 60,
  "Points": "0,30 100,30 100,0 200,0 200,60 300,60",
  "StrokeTheme": "Water", "StrokeThickness": 6,
  "StrokeLineJoin": "Round", "StrokeLineCap": "Round" },

{ "Type": "Polygon", "Left": 490, "Top": 53, "Width": 20, "Height": 14,
  "Points": "0,0 20,7 0,14", "Stretch": "None",
  "FillTheme": "Water",
  "Dynamics": [
    { "Type": "VisibilityDynamic", "LinkedValue": "@Tag.Pipe1/FlowRate" }
  ] }

The arrow only appears when FlowRate is non-zero — a simple, strong visual cue.

For multi-colored pipe based on flow threshold:

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"Dynamics": [
  { "Type": "LineColorDynamic", "LinkedValue": "@Tag.Pipe1/FlowRate",
    "ChangeColorItems": [
      { "Type": "ChangeColorItem", "ChangeLimit": 0,   "LimitColor": "#FF64748B" },
      { "Type": "ChangeColorItem", "ChangeLimit": 10,  "LimitColor": "#FF38BDF8" },
      { "Type": "ChangeColorItem", "ChangeLimit": 50,  "LimitColor": "#FF0369A1" }
    ] }
]

Recipe 4 — Reactor with heating coils

Uses Recipe 1 (vessel) + Path overlay for coils:

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{ /* Recipe 1 elements for vessel body with jacket */ },

{ "Type": "Path", "Left": 305, "Top": 220, "Width": 130, "Height": 240,
  "Data": "M0,0 Q65,20 130,0 M0,40 Q65,60 130,40 M0,80 Q65,100 130,80 M0,120 Q65,140 130,120 M0,160 Q65,180 130,160 M0,200 Q65,220 130,200",
  "StrokeTheme": "StateRed",
  "StrokeThickness": 2,
  "Fill": "#00000000", "FillTheme": "",
  "Dynamics": [
    { "Type": "VisibilityDynamic", "LinkedValue": "@Tag.Reactor/Heater/Running" }
  ] }

The coils are only visible when the heater is active — a subtle but unmistakable visual cue for operators.

Section 6 — Dynamics reference

Call list_dynamics() for the full list. Here are the 14 types grouped by what they do:

Action category

Color category

Animation category (Canvas-only)

Data category (Canvas-only)

Visibility, Security, Feedback

Copy-paste patterns

status_indicator (shape that changes color on running/stopped):

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{
  "Type": "Ellipse",
  "Left": 100, "Top": 100, "Width": 24, "Height": 24,
  "Dynamics": [
    { "Type": "FillColorDynamic", "LinkedValue": "@Tag.Equipment/Running",
      "ChangeColorItems": [
        { "Type": "ChangeColorItem", "ChangeLimit": 0, "LimitColor": "#FF808080" },
        { "Type": "ChangeColorItem", "ChangeLimit": 1, "LimitColor": "#FF34D399" }
      ] }
  ]
}

toggle_button (click toggles a boolean, color reflects state):

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{
  "Type": "Rectangle",
  "Left": 100, "Top": 200, "Width": 120, "Height": 40,
  "Dynamics": [
    { "Type": "ActionDynamic",
      "MouseLeftButtonDown": { "Type": "DynamicActionInfo", "ActionType": "ToggleValue", "ObjectLink": "@Tag.Motor/Start" } },
    { "Type": "FillColorDynamic", "LinkedValue": "@Tag.Motor/Start",
      "ChangeColorItems": [
        { "Type": "ChangeColorItem", "ChangeLimit": 0, "LimitColor": "#FFEF4444" },
        { "Type": "ChangeColorItem", "ChangeLimit": 1, "LimitColor": "#FF34D399" }
      ] },
    { "Type": "ShineDynamic" }
  ]
}

animated_motor (continuous rotation gated by boolean):

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{
  "Type": "Symbol",
  "SymbolName": "Wizard/MOTOR",
  "Left": 400, "Top": 300, "Width": 80, "Height": 80,
  "Dynamics": [
    { "Type": "RotateDynamic", "LinkedValue": "30", "IsRpm": true, "OnOffLink": "@Tag.Motor/Running" }
  ]
}

level_bar (tank-fill effect):

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{
  "Type": "Rectangle",
  "Left": 200, "Top": 200, "Width": 120, "Height": 240,
  "Dynamics": [
    { "Type": "BargraphDynamic", "LinkedValue": "@Tag.Tank/Level",
      "MinValueLink": "0", "MaxValueLink": "100",
      "BarColor": "#FF38BDF8",
      "Orientation": "VerticalUp" }
  ]
}

ActionDynamic action types

Mouse events beyond MouseLeftButtonDown: MouseRightButtonDown, MouseDoubleClick, MouseEnter, MouseLeave. Each is a top-level key on the ActionDynamic.

Format rules

• Dynamics go in the Dynamics array. Never as direct properties on the element.
• ChangeColorItems is a flat array. Not {"Type": "ColorChangeList", "Children": [...]}.
• An element can have MULTIPLE dynamics of different types in the same Dynamics array.

Section 7 — Navigation: headers own page links

Page-to-page navigation belongs in the Header display, not on content pages. Content pages only get in-page actions (start/stop, open popup, acknowledge).

Workflow

1. Build all your content pages first.
2. Read the Startup layout: get_objects('DisplaysLayouts', names=['Startup'], detail='full').
3. Read the Header display: get_objects('DisplaysList', names=['Header'], detail='full').
4. Add navigation buttons right-aligned in the header (100–130 × 30–35, 10px gap).
5. Write the modified Header display back.

Back-navigation on detail pages

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{
  "Type": "TextBlock",
  "Left": 48, "Top": 32, "Width": 400, "Height": 20,
  "LinkedValue": "

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← 

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Process 

...

Area 

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Overview",
  "ForegroundTheme": "AccentBrush",
  "Dynamics": [
    { "Type": "ActionDynamic",
      "MouseLeftButtonDown": { "Type": "DynamicActionInfo", "ActionType": "OpenDisplay", "ObjectLink": "

...

ProcessAreaOverview" } }
  ]
}

Section 8 — Canvas quirks and write-time normalizations

• Cylinder / Gear / Arrow / Cloud / Star / Hexagon / Pentagon / Trapezoid become Path or Polygon on disk. Auto-geometry expanded.
• SvgGroup → ShapeGroup on save. SVG parsed into native WPF shapes.
• Theme brushes stored with theme: prefix: {"FillTheme": "ElementBlue"} → {"Fill": "theme:ElementBlue"}.
• Stretch: "Fill" default silently dropped on Polygon/Polyline/Path/Spline. If you want Stretch: "None", it IS stored.
• Background default #FFFAFAFA baked in. Explicitly set Background: "theme:PageBackground".
• Polygon without Points silently skipped. Always include Points.

Section 9 — Canvas checklist

• ? Background set explicitly (not #FFFAFAFA default)
• ? Zones calculated to fill the full canvas width and height
• ? Every zone has a background Rectangle with FillTheme: "PanelBackground" — FIRST in Elements
• ? Symbols ≥ 60×60 (Wizard), ≥ 80×80 recommended on process overview displays
• ? Library symbols scaled proportionally — maintain aspect ratio
• ? No equipment symbols overlap unless intentionally layered
• ? Zone titles FontSize ≥ 14, value text FontSize ≥ 12
• ? Value and Unit in the SAME TextBlock with composite LinkedValue
• ? No element extends beyond the display's Width/Height
• ? Page navigation is in the Header, not on content pages
• ? All dynamics inside Dynamics array (never as direct properties)
• ? ChangeColorItems is a flat array (no ColorChangeList wrapper)
• ? No use of @Label. in element bindings (only @Tag.)
• ? No binding to UDT-inherited members (TDEV-1272 workaround: direct members only)
• ? No binding to tag system columns like .SourceIri (TDEV-1273 workaround: literal text)
• ? No use of phantom types: Triangle, Octagon, Parallelogram, Hill, Curve, Senoid, Wave, T-Junction (TDEV-1274)All shape / symbol types verified via list_elements() before use
• ? get_state after write shows errorList empty

Section 10 — Quick reference

The 10 element types you'll actually use on most Canvas displays

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Rectangle         - backgrounds, bars, pipes (when rectangular)
Ellipse           - caps, LEDs, pump bodies
Polygon           - arrows, funnels, custom closed shapes
Gridline          - pipes (always prefer over Polyline)
Path              - curves, coils, complex shapes
Cylinder          - vessels, tanks (first-class shortcut)
TextBlock         - all text (labels, values, composite)
Symbol            - Wizard/Library/Solution symbols
ShapeGroup        - composed equipment with unified dynamics
RadialGauge       - temperature, pressure, any circular gauge

Tool-call recipes

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# Before first use of an element
list_elements('RadialGauge')

# Before first use of a dynamic
list_dynamics('FillColorDynamic')

# Pattern search in library
list_elements('Library/HMI/Pumps')

# Wizard catalog (always 5 symbols)
list_elements('Wizard')

# Theme brushes
list_elements('ThemeColors')