Zooming WinCC Runtime Screens: V7 Classic to Unified V20

1. Overview

Runtime screen zoom is one of the most common HMI enhancement requests on plant-floor displays: operators want a single-click magnification of a trend, an alarm summary, or a process overview without losing context. In the Siemens WinCC ecosystem the implementation differs substantially between WinCC V7 classic (TIA Portal's predecessor SCADA), the modern WinCC Unified V20 runtime in TIA Portal, and the connected AVEVA InTouch HMI runtime that many plants have running alongside. This reference consolidates all three implementation paths, focusing on the original problem statement: toggling a 500x500 pixel trend screen to 1000x1000 pixels and back, with a single button click.

The article covers the internal-tag toggle method (the approach explicitly referenced in the field report), the C script SetPropWord path for the PictureWindow Zoom property, the VBScript HMIRuntime path for V7, the TIA Portal V20 Inspector "Zoom - allow" property, and the AVEVA InTouch Ctrl + scroll wheel method. Each method is paired with commissioning verification and a fault matrix.

2. Zoom Methods Across Platforms

Before writing any code, identify which runtime is in scope. The zoom mechanism is not portable across product generations.

Reference: Configuring zooming and scrolling for runtime (RT Unified) - TIA Portal V20 documents the Inspector property in TIA Portal V20. Reference: Zoom at runtime - AVEVA Documentation documents the InTouch Ctrl+wheel behavior.

3. Prerequisites

Before any code is written, confirm the following on the engineering station and the runtime target.

1. WinCC V7.4 SP1 or later for full SetPropWord/SetPropDouble support on PictureWindow Zoom. Earlier V7 versions expose the property as read-only at runtime.
2. TIA Portal V20 engineering license for the Unified runtime path; the Inspector property is not present in V17 or earlier.
3. WinCC Graphics Designer with the same version as the runtime RT (mismatches cause silent script failures).
4. Internal tag license for "HEIGHT_WIDTH" (or equivalent). The field report explicitly names an "Unsigned 16-bit Value" internal tag named HEIGHT_WIDTH.
5. Picture Window on the parent screen for the V7 internal-tag method, with the trend screen assigned as its Picture Name property and Independent picture window flag enabled.
6. WinCC V7 scripting runtime enabled in the project properties (Project > Properties > Options > Activate scripting). If disabled, C and VBS events fire silently.

4. WinCC V7 Classic - Internal-Tag Toggle Method

The field report's recommended approach is the simplest, most portable pattern for V7. It uses one internal tag to encode the current zoom state and a single button that toggles it. A C action (cyclic or tag-triggered) reads the tag and resizes the Picture Window.

4.1 Create the Internal Tag

1. Open Tag Management > Internal Tags.
2. Create a new tag: HEIGHT_WIDTH
3. Data type: Unsigned 16-bit Value
4. Start value: 500 (initial trending screen size in pixels)
5. Update cycle: do not set (internal tags are event-driven)

4.2 Wire the Toggle Button

On the parent screen, draw a button ("Zoom"). Under Events > Mouse > Press left, attach a C action:

// V7 C action - toggle zoom state
#include "apdefap.h"
void OnClick(char* lpszPictureName, char* lpszObjectName, char* lpszPropertyName)
{
    DWORD current = GetTagWord("HEIGHT_WIDTH");
    if (current == 500)
    {
        SetTagWord("HEIGHT_WIDTH", 1000);
    }
    else
    {
        SetTagWord("HEIGHT_WIDTH", 500);
    }
}

4.3 Apply the Tag Value to the Picture Window

On the Picture Window's Width and Height properties, set a tag connection to HEIGHT_WIDTH. WinCC will scale the window from 500x500 to 1000x1000 and back on each toggle.

4.4 Verification (V7 Internal-Tag Method)

1. Activate the project and open the parent screen.
2. Click the Zoom button once - the Picture Window grows from 500 to 1000 px in both axes.
3. Confirm HEIGHT_WIDTH reads 1000 in WinCC Explorer > Tag Management > Internal Tags.
4. Click again - the window collapses to 500 px and the tag returns to 500.
5. Verify the trend continues to update during the transition (no frozen curves).

5. WinCC V7 Classic - C Script SetPropWord Path

For cases where the picture is not embedded in a Picture Window, or where more than one screen must zoom simultaneously, use the SetPropWord function on the Zoom property of the picture or PictureWindow object.

// V7 C action - explicit Zoom property
#include "apdefap.h"
void OnClick(char* lpszPictureName, char* lpszObjectName, char* lpszPropertyName)
{
    // Zoom value range: 10 to 800 (percent), 100 = no zoom
    // 500x500 source on a 1000x1000 host = 200% zoom
    float current = (float)GetPropDouble(lpszPictureName, "PictureWindow1", "Zoom");
    if (current < 150.0f)
    {
        // Zoom in to 200%
        SetPropDouble(lpszPictureName, "PictureWindow1", "Zoom", 200.0f);
    }
    else
    {
        // Zoom out to 100%
        SetPropDouble(lpszPictureName, "PictureWindow1", "Zoom", 100.0f);
    }
}

5.1 Property Reference

6. WinCC V7 Classic - VBScript Approach

VBScript is the recommended path for V7 projects that mix WinCC with Office automation or that have C-scripting disabled by IT policy. The HMIRuntime object model exposes the same Zoom property through the ScreenItems collection.

' V7 VBS action - toggle Zoom via HMIRuntime
Sub OnClick(ByVal Item)
    Dim objPW
    Set objPW = HMIRuntime.Screens("MainOverview").ScreenItems("PictureWindow1")

    If objPW.Zoom < 150 Then
        objPW.Zoom = 200         ' 200% (1000x1000 of a 500x500 base)
        objPW.Left = (objPW.Parent.Width - objPW.Width) / 2
        objPW.Top  = (objPW.Parent.Height - objPW.Height) / 2
    Else
        objPW.Zoom = 100         ' 100% (500x500 base)
        objPW.Left = 100
        objPW.Top  = 100
    End If
End Sub

6.1 VBS Property Reference

7. WinCC Unified V20 - Inspector Zoom Property

The TIA Portal V20 Unified runtime takes a different approach. Zoom is a container property activated in the Inspector, not a scriptable attribute. Configure it as follows.

1. Open the main screen in the TIA Portal editor.
2. Select the screen window (not individual objects).
3. Open the Inspector window.
4. Navigate to Properties > Format.
5. Locate the "Zoom - allow" property and set it to true (the option is enabled by default per the official TIA Portal V20 documentation).
6. Optionally restrict the zoom range with Zoom - minimum and Zoom - maximum if uncontrolled zoom-out is a concern.

Reference: Configuring zooming and scrolling for runtime (RT Unified) - TIA Portal V20.

7.1 JavaScript Trigger in Unified V20

Unified screens use JavaScript in the Events tab. To bind a button to the zoom toggle:

// Unified V20 - JavaScript on a button "Click" event
export function ZoomToggle_OnClick(item) {
    let screen = item.Parent;
    let currentZoom = screen.ZoomFactor;   // read current
    if (currentZoom < 1.5) {
        screen.ZoomFactor = 2.0;           // 200%
    } else {
        screen.ZoomFactor = 1.0;           // 100%
    }
    // recenter the visible area on the trend
    screen.HorizontalScrollPosition = 0;
    screen.VerticalScrollPosition = 0;
}

8. AVEVA InTouch HMI - Ctrl + Scroll Wheel

AVEVA InTouch provides runtime zoom with no configuration beyond default installation. Operators zoom by holding Ctrl and scrolling the mouse wheel; the view zooms in from the cursor anchor, which mirrors the behavior of a magnifier lens.

Reference: Zoom at runtime - AVEVA Documentation.

For a single-button toggle in InTouch, use the AnimationLinks - Discrete Value or an Action Script that sets the WindowPainter magnification factor. InTouch does not expose a SetZoom equivalent through the standard animation palette; custom script is required:

' AVEVA InTouch QuickScript - window magnification toggle
IF $WindowMagFactor < 1.5 THEN
    SetWindowMag 2.0;
ELSE
    SetWindowMag 1.0;
ENDIF;

9. Trend Screen Implementation: 500x500 to 1000x1000

Apply the V7 internal-tag method to the original problem statement. The trend screen is a child PDL with one WinCC Online Trend Control (object name TrendControl1). The parent screen has one Picture Window and one button.

9.1 Parent Screen - Object Inventory

9.2 Tag Connection on Picture Window

Bind PW_Trend Width and Height to HEIGHT_WIDTH. WinCC will re-layout the window when the value changes. Set Picture Name to Trend.pdl.

9.3 Button C-Action

#include "apdefap.h"
void OnClick(char* lpszPictureName, char* lpszObjectName, char* lpszPropertyName)
{
    DWORD size = GetTagWord("HEIGHT_WIDTH");
    DWORD newSize = (size == 500) ? 1000 : 500;
    SetTagWord("HEIGHT_WIDTH", newSize);
    SetText(lpszPictureName, "txt_Status",
            newSize == 1000 ? "Zoomed: 1000x1000" : "Normal: 500x500");
}

9.4 Verification Checklist

1. Runtime, click btn_Zoom: PW_Trend snaps to 1000x1000, trend redraws at higher resolution.
2. Status text reads "Zoomed: 1000x1000".
3. Click again: PW_Trend collapses to 500x500, status returns to "Normal: 500x500".
4. Operator workflow: trend remains interactive at both sizes, no dialog boxes interrupt the toggle.
5. On screen change and return: HEIGHT_WIDTH retains its last value (internal tags persist for the runtime session).

10. Common Errors and Verification Matrix

11. Performance and Safety Considerations

11.1 CPU Impact

WinCC V7 repaints the entire screen on each Zoom change. On a 1920x1080 panel with 4 trend controls, a 100% to 200% transition can consume 80-150 ms of CPU on a Core i5-6500. The internal-tag method triggers a single property change; the C-script SetPropDouble method triggers a full screen redraw. Prefer the internal-tag method for frequently toggled zoom.

11.2 Memory Footprint

Each Picture Window allocates a back-buffer bitmap equal to its current size. Doubling 500x500 to 1000x1000 quadruples the bitmap footprint (4x the pixel count). On panels with 4 GB RAM or less, rapid toggling can fragment the heap. Test with the largest expected configuration before commissioning.

11.3 Operator Safety

Zoom should never block acknowledgement of an alarm. Add the following guard in the button event:

// C-Action - guard against zoom during active alarm
DWORD size = GetTagWord("HEIGHT_WIDTH");
DWORD alarmCount = GetTagWord("ALARM_UNACK_COUNT");
if (alarmCount > 0 && size == 500) {
    return;  // Block zoom-out; keep operator on 1000x1000 for visibility
}
SetTagWord("HEIGHT_WIDTH", (size == 500) ? 1000 : 500);

11.4 Multi-Monitor Consistency

If the same project runs on a 22" panel and a 65" overview wall, the 100% zoom on the 65" wall shows the same pixel count as 200% on the 22" panel. Use a project-level constant ZOOM_BASE_PERCENT to normalize the visual size across display classes.

12. Migration Notes: V7 to Unified V20

Projects migrated from V7 to TIA Portal Unified lose the Picture Window Zoom property and the C-script SetPropWord / SetPropDouble path. Convert internal-tag-driven size changes to ScreenItem.ZoomFactor in JavaScript, and use the Inspector Zoom - allow property for operator touch/ctrl-wheel fallback.

13. FAQ