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Feature Request: Heatmap Rendering Order Control

Summary

Add parameters to control the rendering order (z-order) of points in the Heatmap component, allowing users to specify which points should be drawn on top when overlapping.

Use Case

When visualizing peptide-spectrum match (PSM) identification results, we display a heatmap with:

  • x-axis: Retention time (RT)
  • y-axis: Mass-to-charge ratio (m/z)
  • intensity: Score (e-value, PEP, or q-value)

For these score types, lower values indicate better identifications. Currently, when points overlap, there's no control over which points are rendered on top. Ideally, we want the best identifications (lowest scores) to be visible on top of worse ones.

Current Workaround

We can reverse the colorscale using colorscale="Portland_r" to make low scores appear with high-intensity colors, but this doesn't address the overlapping point visibility issue.

Proposed Solution

Add one or more of the following parameters to the Heatmap component:

Option 1: sort_column and sort_ascending

Heatmap(
    data=df,
    x_column="rt",
    y_column="mz",
    intensity_column="score",
    sort_column="score",      # Column to sort by for rendering order
    sort_ascending=False,     # False = high values rendered first (low on top)
)

Option 2: render_order

Heatmap(
    data=df,
    x_column="rt",
    y_column="mz",
    intensity_column="score",
    render_order="intensity_asc",  # Options: "intensity_asc", "intensity_desc", "data_order"
)

Option 3: top_layer

Heatmap(
    data=df,
    x_column="rt",
    y_column="mz",
    intensity_column="score",
    top_layer="low_intensity",  # Options: "low_intensity", "high_intensity"
)

Additional Context

  • This is particularly important for proteomics workflows where score distributions often have many overlapping points
  • The feature would complement the existing colorscale parameter for full control over visual representation
  • Consider how this interacts with the multi-resolution downsampling - perhaps the sort should be applied before binning/downsampling

Environment

  • openms-insight version: >= 0.1.10
  • Application: quantms-web (DDA-LFQ) built on streamlit-template