HMI canvas not refreshing after moving an object

Why does the canvas keep the old position after I move an object?

The edit has been written to the project and the view has stopped redrawing. In the reported case the thumbnail showed the move while the canvas kept the old position. The trigger was the open help pane, whose browser component was stalling the redraw.

The proof of the split is the thumbnail. It draws the same screen from the project data. When it shows the new position, the move landed in the file and the canvas is the only thing out of date. The case behind this article ran on Windows 7 on 3 laptops of one product line. The fault showed on all three and on no desktop. It survived a clean reinstall from a freshly downloaded installer, a full round of Windows updates, and a move to a later editor version. Steps aimed at the installation changed nothing, which moved the search to the windows sitting beside the canvas.

How do I tell a stale canvas from a bad edit?

Make one small, reversible move on a test object and compare the thumbnail with the canvas. If the thumbnail shows the new position and the canvas shows the old one, the project accepted the edit and only the picture is stale. The whole check takes under 10 seconds.

Work on a scratch screen so a mistake costs nothing:

1. Open an unused screen, or an empty corner of the one you are editing.
2. Drop a plain rectangle or a button on it.
3. Drag it once, a short distance of about 50 pixels, and let go.
4. Compare the thumbnail with the canvas.

Thumbnail moved and canvas did not: the view is stale, and the help-pane test below applies. Neither moved: undo once and repeat the move. A plain object that never moves in either view points at the object, for example one that is grouped or locked, so retest on a fresh rectangle before blaming the display.

Stop editing the production screen the moment the disagreement appears. An object placed by dragging against a stale canvas can sit somewhere you never intended. On an operator screen a misplaced indicator misleads the person running the machine.

What does each symptom point to?

Match what you see against this list before changing anything. The split between an updating thumbnail and a frozen canvas is the one this article solves.

• Thumbnail shows the move, canvas keeps the old position. The project has the edit and the view stopped redrawing. Run the help-pane test.
• Anchor or selection points fail to appear although the object is selected. Selection still works, as the help pane following the selection showed in the reported case; only the drawing lags. Same stall.
• The dragged object appears at its old spot until you change screens and come back. The editor redraws only when the view is rebuilt. Same stall.
• Thumbnail and canvas both keep the old position. The edit never reached the project. Undo once and redo the move on a fresh plain object. If both views then agree on the new position, the object was the problem.
• Other programs on the same PC refresh in loops or smear when you scroll. The fault sits in that PC's display stack and the editor is caught in it. Update Windows and the graphics driver on that machine first.
• Numeric values on the running panel hold old values after a screen change. That is a fault on the terminal, with its own diagnosis, covered in HMI numeric displays show old values after a screen change.

How do I force one redraw to confirm the edit landed?

Scroll past the bottom edge of the screen in the editor and back up, or switch to another screen and return. Both actions rebuilt the view and showed the moved object at its new position in the documented case, each in about 2 seconds.

Both are workarounds, and they earn their place in the test sequence:

1. Make the single test move.
2. Scroll below the extents of the screen and back up, or switch screens and return.
3. Confirm the object now sits at its new position on the canvas.
4. Note the result, then move on to the help-pane test.

Use the workaround once, to prove the edit landed. Repeating a scroll after every drag leaves the trigger in place and turns every layout session into extra operations. The note of what each view showed before and after the scroll is the record you compare against once the pane is closed.

Why does closing the help pane restore the refresh?

The help pane that shows the selected object's properties embeds a browser component. In the reported case that embedded browser was the surface stalling the canvas. With the pane closed, refresh came back correct on every affected laptop.

The trail in the reported case: the stall first appeared whenever a separate browser window was open beside the editor. Closing the browser reduced it, but running the editor alone after every reboot was impractical as a daily workflow. The software vendor's support then pointed at the pane titled "Object Help" in that editor. It embeds browser components, so it reproduces the browser's effect with no separate browser running. With the pane closed, the same one-object move passed on the first attempt and on every repeat after.

Run it on your own setup, about 5 minutes in all:

1. Close the properties or help pane beside the canvas, and close any open browser window.
2. Repeat the single reversible move 3 times.
3. If the canvas follows all three, keep the pane closed for the rest of the session. Reopen the pane only to read a property, then close it again.
4. If nothing changes, leave the pane where it is and go to the PC comparison below.

A pane that itself refuses to open, or opens empty, is a separate fault with its own checks, covered in Fix an HMI help file that will not open.

Example: the full sequence on a 15 MB project

The documented case was an editor at version 2.73 on Windows 7, a project of about 15 MB carrying many dynamic bitmap symbols, and the fault on 3 laptops of one product line while every desktop stayed clean.

Carried through step by step:

1. One reversible move on a test object: thumbnail updated, canvas kept the old position. Stale view confirmed, project untouched.
2. Scroll beyond the screen extents and back: the object appeared at its new position. The edit had landed; workaround recorded.
3. Clean reinstall from a freshly downloaded installer, about 20 minutes of work: the fault returned on the same move. The installation was not the trigger.
4. Update from version 2.73 to 2.76 with a browser window open: the same stall. The software version was not it either.
5. Help pane closed, browser closed, same move repeated 3 times: the canvas followed the object at once, and on every repeat after.
6. Same 15 MB project on a desktop: clean throughout, pane open or closed.

The 15 MB project stayed exactly as it was. Nothing was trimmed and no screen was rebuilt. The trigger was the help pane and its embedded browser surface, open beside the canvas on those laptops and absent on the desktops.

Which checks separate a laptop problem from a project problem?

Run the pane-closed test on a second PC with a copy of the same project. If the canvas follows edits on the desktop and stalls on the laptop, the trigger lives in the laptop's own display environment, and the project file is clean.

The vendor's first suggestions in the case were a complete reinstall and a second PC, to rule out a machine-specific graphics driver. The reinstall changed nothing and the desktop stayed clean, so the pane test settled it. When your own pane test comes back negative, this table decides what each result means:

Editor display faults with a Windows setting behind them come up more than once. HMI editor shows objects but no text: check Windows DPI is the DPI scaling case, and it rewards the same habit: one variable at a time.

When can I go back to normal screen editing?

Return to normal editing when the canvas has followed 3 single-object moves in a row with the help pane closed and no browser window open. From then on, edit with the pane closed and open it only to look up a property.

Before you edit production screens at normal pace, confirm each edited screen with one reversible move and the thumbnail comparison. Download only a screen whose canvas agreed with its thumbnail. Keep the notes from the tests: editor version, Windows edition, whether a browser window was open, whether the pane was open, and the project size in MB. If the fault ever returns, that record reproduces the conditions for the vendor without another week of isolation.

Recommendation: When the thumbnail shows your move and the canvas keeps the old position, stop dragging, run the one-object test, close the help pane and any open browser window, and repeat the same move 3 times. If the canvas follows the object with the pane closed, keep it closed for the rest of the session and verify each screen with one reversible move before you download to the panel. If the canvas is still stale with the pane closed on 2 PCs, stop editing, save a project copy, and send it to the software vendor's support with the editor version and the test results.

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