display

Stores the latest input value for display.

📝Syntax

Block type: display

📥Input Arguments

Parameter	Description
input ports	1 input port(s) declared.

📄Description

Stores the latest input value for display.

Module	`nflow_blocks`
Library	Sink blocks
Type	`display`
Label	Display

Description

The Display block shows a single scalar value during simulation. It's intended for quick inspection of signals (numeric outputs) in the diagram.

Ports

Input(s)

Port	Role	Side	Position
Port_1	Numeric signal read by the block.	left	x=0, y=30

Output(s)

This block declares no output ports.

Parameters

Parameter	Default value
`label`	Display
`format`	short
`decimation`	1
`floatingDisplay`	false

Inspector Keys

These serialized keys are exposed by the block inspector.

label
format
decimation
floatingDisplay

Block Characteristics

Block type	display
Family	Sink blocks
Rendered size	120 x 60
Phases	INIT, AFTER_STEP
Direct feedthrough	see Algorithms
Internal state or history	yes
Signal data type	double numeric values

Algorithms

INIT clears the stored scalar.
AFTER_STEP samples input 1 according to decimation; values below 1 behave as 1.
The block has no output ports.

Extended Capabilities

This page describes the native runtime behavior observed in the module C++ sources. Declared phases indicate when the simulation engine calls the block.

Code generation: supported for C and Rust.

Implementation Sources

Manifestmodules/nflow_blocks/libraries/sink/library.json

{
  "id": "builtin.sink",
  "title": "Sinks",
  "version": "1.0.0",
  "format": "nflow-2",
  "metadata": {
    "author": "Allan CORNET",
    "created": "2026-03-21",
    "tool": "Nelson nflow"
  },
  "comment": "Blocks for visualizing or exporting simulation results",
  "license": "LGPL-3.0",
  "builtin": true,
  "blocks": [
    {
      "type": "scope",
      "label": "Scope",
      "icon": "scope.svg",
      "phases": [
        "INIT",
        "AFTER_STEP"
      ],
      "width": 220,
      "height": 160,
      "inputs": [
        {
          "x": 0,
          "y": 40,
          "side": "left"
        },
        {
          "x": 0,
          "y": 80,
          "side": "left"
        },
        {
          "x": 0,
          "y": 120,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "TMin": "",
        "TMax": "",
        "YMin": "",
        "YMax": "",
        "width": 220,
        "height": 160,
        "ShowTickLabels": false
      },
      "render": {
        "type": "plot",
        "path": "M{axisX} {axisTop} L{axisX} {axisY} L{axisRight-2} {axisY}"
      }
    },
    {
      "type": "xyScope",
      "icon": "xyScope.svg",
      "label": "XY Scope",
      "phases": [
        "INIT",
        "AFTER_STEP"
      ],
      "width": 220,
      "height": 160,
      "inputs": [
        {
          "x": 0,
          "y": 50,
          "side": "left"
        },
        {
          "x": 0,
          "y": 110,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "XMin": "",
        "XMax": "",
        "YMin": "",
        "YMax": "",
        "width": 220,
        "height": 160,
        "ShowTickLabels": false
      },
      "render": {
        "type": "plot",
        "path": "M{axisX} {axisY} L{axisRight-2} {axisTop+8}"
      }
    },
    {
      "type": "xyzScope",
      "label": "XYZ Scope",
      "icon": "xyzScope.svg",
      "phases": [
        "INIT",
        "AFTER_STEP"
      ],
      "width": 220,
      "height": 180,
      "inputs": [
        {
          "x": 0,
          "y": 50,
          "side": "left"
        },
        {
          "x": 0,
          "y": 90,
          "side": "left"
        },
        {
          "x": 0,
          "y": 130,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "XMin": "",
        "XMax": "",
        "YMin": "",
        "YMax": "",
        "ZMin": "",
        "ZMax": "",
        "width": 220,
        "height": 180,
        "RotationX": 30,
        "RotationY": 45
      },
      "render": {
        "type": "plot",
        "path": "M{axisX} {axisY} L{axisRight-2} {axisY-20}"
      }
    },
    {
      "type": "fileSink",
      "icon": "fileSink.svg",
      "label": "Output File",
      "phases": [],
      "width": 80,
      "height": 80,
      "inputs": [
        {
          "x": 0,
          "y": 40,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "FileName": "output.csv"
      },
      "render": {
        "type": "image",
        "src": "fileSink.svg"
      }
    },
    {
      "type": "labelSink",
      "icon": "labelSink.svg",
      "label": "Label Sink",
      "phases": [],
      "width": 40,
      "height": 40,
      "inputs": [
        {
          "x": 0,
          "y": 20,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "GotoTag": "x",
        "ShowNode": true
      },
      "render": {
        "type": "math",
        "bodyClass": "block-body",
        "mathGroupClass": "label-sink-math",
        "formula": "{params.GotoTag}"
      }
    },
    {
      "type": "display",
      "icon": "display.svg",
      "label": "Display",
      "phases": [
        "INIT",
        "AFTER_STEP"
      ],
      "width": 120,
      "height": 60,
      "inputs": [
        {
          "x": 0,
          "y": 30,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "Label": "Display",
        "Format": "short",
        "Decimation": 1,
        "Floating": false
      },
      "render": {
        "type": "math",
        "bodyClass": "block-body",
        "mathGroupClass": "display-math",
        "formula": "\\mathsf{Disp}"
      }
    },
    {
      "type": "toWorkspace",
      "label": "To Workspace",
      "icon": "toWorkspace.svg",
      "phases": [
        "INIT",
        "AFTER_STEP"
      ],
      "width": 80,
      "height": 48,
      "inputs": [
        {
          "x": 0,
          "y": 24,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {
        "VariableName": "simout",
        "MaxDataPoints": "inf",
        "Decimation": 1,
        "SaveFormat": "Structure With Time",
        "SampleTime": "-1"
      },
      "render": {
        "type": "math",
        "formula": "\\mathtt{{params.VariableName}}",
        "textSize": 14
      }
    },
    {
      "type": "terminator",
      "label": "Terminator",
      "icon": "terminator.svg",
      "phases": [],
      "width": 40,
      "height": 40,
      "inputs": [
        {
          "x": 0,
          "y": 20,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {},
      "render": {
        "type": "image",
        "src": "exports/terminator.svg",
        "svgMode": "element",
        "preserveAspectRatio": "none",
        "x": 0,
        "y": 0,
        "width": 40,
        "height": 40
      }
    },
    {
      "type": "stopSimulation",
      "label": "Stop",
      "icon": "stopSimulation.svg",
      "phases": [
        "AFTER_STEP"
      ],
      "width": 40,
      "height": 40,
      "inputs": [
        {
          "x": 0,
          "y": 20,
          "side": "left"
        }
      ],
      "outputs": [],
      "defaultParams": {}
    }
  ]
}

Runtimemodules/nflow_blocks/src/cpp/sink/display.cpp

//=============================================================================
// Copyright (c) 2016-present Allan CORNET (Nelson)
//=============================================================================
// This file is part of Nelson.
//=============================================================================
// LICENCE_BLOCK_BEGIN
// SPDX-License-Identifier: LGPL-3.0-or-later
// LICENCE_BLOCK_END
//=============================================================================
#include "SimEngineTypes.hpp"
#include "BlockRegistry.hpp"
#include "FieldNames.hpp"
#include "NFlowBlockDescriptor.hpp"
#include <cmath>
#include <algorithm>
#include "sink_blocks.hpp"
//=============================================================================
bool
Nelson::NFlow::handleDisplay(SimCtx& ctx, const Block& b, Phase phase)
{
    auto& st = getState(ctx, b.nid);
    if (phase == Phase::INIT) {
        st.scalar = std::numeric_limits<double>::quiet_NaN();
        st.scalar2 = 0.0; // decimation step counter
        return false;
    }
    if (phase == Phase::AFTER_STEP) {
        nflow::BlockDescriptor bd(b, ctx.variables);
        int decimation = static_cast<int>(bd.paramDouble(nflow::kDecimation, 1.0));
        if (decimation < 1) {
            decimation = 1;
        }
        st.scalar2 += 1.0;
        if (static_cast<int>(st.scalar2) % decimation == 0) {
            SigView v = getInputSig(ctx, b.nid, 0);
            if (v.width > 1) {
                st.displayValues.assign(v.data, v.data + v.width);
                st.scalar = v.data[0];
            } else {
                st.displayValues.clear();
                st.scalar = hasInput(ctx, b.nid, 0) ? getInput(ctx, b.nid, 0, 0.0)
                                                    : std::numeric_limits<double>::quiet_NaN();
            }
        }
        return false;
    }
    return false;
}
//=============================================================================
Nelson::NFlow::BlockCodegenTemplate
Nelson::NFlow::getCodeGenCDisplay()
{
    BlockCodegenTemplate t;
    t.step = "out_{id} = {in0};";
    return t;
}
//=============================================================================
Nelson::NFlow::BlockCodegenTemplate
Nelson::NFlow::getCodeGenRustDisplay()
{
    BlockCodegenTemplate t;
    t.step = "out_{id} = {in0};";
    return t;
}
//=============================================================================

🔗See Also

scope terminator fileSink

🕔Version History

Version	Description
1.0.0	initial version

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