ValueAxis label and tick misalignment when modifying range in Qt Graphs (QML)
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Overview
When working with ValueAxis in Qt Graphs, dynamically modifying the min and max properties can occasionally lead to visual artifacts regarding tick mark and grid line placement. This behavior is most prominent when the configured tickInterval is not an exact divisor of the calculated axis range (i.e., (max - min) % tickInterval != 0).Technical Context
The ValueAxis component calculates tick positions based on the tickInterval and a reference point known as the tickAnchor. By default, the tickAnchor may persist from a previous state or default to zero. When the range of an axis is updated—specifically in scenarios where the max value is not a clean multiple of the interval relative to the min—the axis may not automatically realign its anchor. This results in visual misalignment where the distance between ticks appears non-uniform or “drifted” relative to the axis bounds.Recommended Implementation
To ensure consistent visual rendering, especially in real-time plotting or dynamic UI updates, it is recommended to explicitly synchronize the tickAnchor with the min value whenever the axis range is modified.Example Pattern:
// Logic to apply when updating the axis range function updateAxisRange(newMin, newMax) { // 1. Update the bounds first axis.min = newMin; axis.max = newMax; // 2. Explicitly force a re-anchor to the new minimum // This ensures that the tick spacing remains uniform starting from the axis start. axis.tickAnchor = newMin; }Best Practices for Dynamic Scaling:
- Atomic Updates: Always update the range properties (min/max) before updating the tickAnchor to ensure the layout engine processes the state changes in the intended order.
- State Management: If you are using a PropertyAnimation to transition your axis range, consider using an onStopped handler or a Binding to update the tickAnchor only after the transition is complete. Performing this update every frame during an animation can cause unnecessary recalculations.
- Validation: If the tickInterval is user-defined or dynamically calculated, ensure that your logic validates that the interval is non-zero to prevent rendering errors.
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Overview
When working with ValueAxis in Qt Graphs, dynamically modifying the min and max properties can occasionally lead to visual artifacts regarding tick mark and grid line placement. This behavior is most prominent when the configured tickInterval is not an exact divisor of the calculated axis range (i.e., (max - min) % tickInterval != 0).Technical Context
The ValueAxis component calculates tick positions based on the tickInterval and a reference point known as the tickAnchor. By default, the tickAnchor may persist from a previous state or default to zero. When the range of an axis is updated—specifically in scenarios where the max value is not a clean multiple of the interval relative to the min—the axis may not automatically realign its anchor. This results in visual misalignment where the distance between ticks appears non-uniform or “drifted” relative to the axis bounds.Recommended Implementation
To ensure consistent visual rendering, especially in real-time plotting or dynamic UI updates, it is recommended to explicitly synchronize the tickAnchor with the min value whenever the axis range is modified.Example Pattern:
// Logic to apply when updating the axis range function updateAxisRange(newMin, newMax) { // 1. Update the bounds first axis.min = newMin; axis.max = newMax; // 2. Explicitly force a re-anchor to the new minimum // This ensures that the tick spacing remains uniform starting from the axis start. axis.tickAnchor = newMin; }Best Practices for Dynamic Scaling:
- Atomic Updates: Always update the range properties (min/max) before updating the tickAnchor to ensure the layout engine processes the state changes in the intended order.
- State Management: If you are using a PropertyAnimation to transition your axis range, consider using an onStopped handler or a Binding to update the tickAnchor only after the transition is complete. Performing this update every frame during an animation can cause unnecessary recalculations.
- Validation: If the tickInterval is user-defined or dynamically calculated, ensure that your logic validates that the interval is non-zero to prevent rendering errors.
Welcome, @MmdMlv81! Thank you for sharing your suggestion.
The visual artifacts sound like a bug. Would you be willing to file a bug report? If so, please log into https://qt-project.atlassian.net/jira/for-you and click "+ Create" at the top of the page.
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Welcome, @MmdMlv81! Thank you for sharing your suggestion.
The visual artifacts sound like a bug. Would you be willing to file a bug report? If so, please log into https://qt-project.atlassian.net/jira/for-you and click "+ Create" at the top of the page.
@JKSH “Thank you for the guidance! I agree that this appears to be a bug in Qt Graphs. However, my project source code is on my work machine, and I won’t have access to it for the next couple of days. I will prepare a minimal reproducible example and file the report on Jira as soon as I get back to my workstation. Thanks again!”
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Hi,
I have submitted the bug report on Jira along with a minimal reproducible example and screenshots:
https://qt-project.atlassian.net/browse/QTBUG-152112Thank you for your guidance!
