pyqtgraph/PySide6 horizontal gradient flickers when data updates and repeats gradient

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Summary

The issue at hand is a flickering horizontal gradient in a PySide6 application using pyqtgraph. The gradient is used to represent the color of light at different wavelengths. When the data updates, the gradient flickers momentarily and is repeated across the X-axis. The cause of this issue is related to the coordinate mode of the QLinearGradient.

Root Cause

The root cause of this issue is the use of QGradient.ObjectMode as the coordinate mode for the QLinearGradient. This mode causes the gradient to be defined in object coordinates, which can lead to unpredictable behavior when the plot is updated. The other modes, QGradient.LogicalMode and QGradient.StretchToDeviceMode, are not being used correctly, resulting in the observed issue.

Why This Happens in Real Systems

This issue occurs in real systems due to the following reasons:

  • Incorrect use of coordinate modes: The coordinate mode of the QLinearGradient is not being used correctly, leading to unpredictable behavior.
  • Insufficient handling of plot updates: The plot updates are not being handled correctly, causing the gradient to flicker and repeat.
  • Lack of understanding of pyqtgraph and QLinearGradient: The developer may not have a thorough understanding of how pyqtgraph and QLinearGradient work, leading to incorrect implementation.

Real-World Impact

The real-world impact of this issue is:

  • Visual distortion: The flickering and repeating gradient can cause visual distortion, making it difficult for users to interpret the data.
  • User experience: The issue can negatively impact the user experience, leading to frustration and decreased productivity.
  • Data accuracy: The issue can also affect the accuracy of the data being displayed, leading to incorrect conclusions.

Example or Code

def get_plot_color_gradient(self):
    grad = QLinearGradient(0, 0, 1, 0)
    for position, color in self.get_wavelength_gradient_stops():
        color.setAlpha(150)
        grad.setColorAt(position, color)
    grad.setCoordinateMode(QGradient.StretchToDeviceMode)  # Change to StretchToDeviceMode
    return QBrush(grad)

How Senior Engineers Fix It

Senior engineers can fix this issue by:

  • Using the correct coordinate mode: Using QGradient.StretchToDeviceMode instead of QGradient.ObjectMode to define the gradient in device coordinates.
  • Handling plot updates correctly: Ensuring that plot updates are handled correctly to prevent the gradient from flickering and repeating.
  • Understanding pyqtgraph and QLinearGradient: Having a thorough understanding of how pyqtgraph and QLinearGradient work to implement the gradient correctly.

Why Juniors Miss It

Juniors may miss this issue due to:

  • Lack of experience: Limited experience with pyqtgraph and QLinearGradient can lead to incorrect implementation.
  • Insufficient knowledge: Not having a thorough understanding of the coordinate modes and how they affect the gradient.
  • Overlooking details: Overlooking the details of the plot updates and how they affect the gradient.

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