[codex] Fix empty heatmap cells leaking splitArea background

[susiwen8]

Summary

• render placeholder heatmap cells for empty values so splitArea bands do not leak through and create inconsistent empty-cell backgrounds
• add a regression test covering the empty heatmap splitArea behavior

Root Cause

Empty heatmap cells on cartesian-style heatmaps were skipped entirely. With splitArea enabled, the alternating axis background showed through those skipped cells, so adjacent empty cells could appear inconsistent.

Validation

• ./node_modules/.bin/jest --config test/ut/jest.config.cjs --runInBand test/ut/spec/series/heatmap.test.ts
• ./node_modules/.bin/eslint src/chart/heatmap/HeatmapView.ts test/ut/spec/series/heatmap.test.ts

Fixes #21290

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[Copilot]

Pull request overview

This PR fixes inconsistent rendering of empty heatmap cells when splitArea is enabled by ensuring “empty” data points still produce placeholder rects (so axis split-area bands don’t show through), and adds a regression test to lock in the behavior.

Changes:

• Render placeholder heatmap rects for empty (NaN) values in cartesian and matrix coordinate systems, using the chart background color (fallback tokens.color.neutral00) as the fill.
• Update progressive rendering path to apply the same empty-cell fill behavior.
• Add a Jest regression test verifying empty cells are rendered and filled to prevent splitArea background leakage.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/chart/heatmap/HeatmapView.ts	Stops skipping empty values on cartesian/matrix heatmaps; renders placeholder rects with a background fill to prevent splitArea bleed-through (including in incremental rendering).
test/ut/spec/series/heatmap.test.ts	Adds regression coverage to ensure empty heatmap cells render as rects and use the expected fill, preventing split-area background leakage.

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[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-21574@adb71c1

[Ovilia]

Can you please provide a screenshot of the colors before and after the change?

[Ovilia]

It should probably use tokens.color.background instead.

[susiwen8]

Updated in adb71c1 to use tokens.color.background as the fallback instead of tokens.color.neutral00.

[susiwen8]

Updated the fallback color in . I also re-ran the case locally with a high-contrast \ palette and a yellow chart background to make the visual difference obvious: before the fix, the empty cells showed the split-area colors directly; after the fix, the empty cells use the chart background instead.

[susiwen8]

Updated the fallback color in adb71c1.

I also re-ran the case locally with a high-contrast splitArea.areaStyle.color palette and a yellow chart background to make the visual difference obvious:

• before the fix, the empty cells showed the split-area colors directly
• after the fix, the empty cells use the chart background instead