feat: TeX/LaTeX formula rendering in chart elements (closes #125)

[timmolter]

Summary

Adds optional TeX/LaTeX math formula rendering to XChart chart elements. Any string wrapped in $...$ is rendered as a LaTeX math formula when the JLatexMath library is present on the classpath; otherwise it falls back gracefully to plain text.

Closes #125.

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Affected chart elements

• Chart title
• Axis titles (X and Y)
• Axis tick labels (X and Y, including category labels)
• Legend entries

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Usage

Wrap any label string in $...$:

XYChart chart = new XYChartBuilder()
    .title("$\\frac{E}{mc^2}$")
    .xAxisTitle("$\\alpha$ (radians)")
    .yAxisTitle("$\\sigma$ (Pa)")
    .build();

chart.addSeries("$\\beta_1$", xData, y1Data);
chart.addSeries("$\\gamma_2$", xData, y2Data);

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Optional dependency

JLatexMath is declared optional so consumers who don't need TeX rendering don't need the jar on their classpath:

<dependency>
  <groupId>org.scilab.forge</groupId>
  <artifactId>jlatexmath</artifactId>
  <version>1.0.7</version>
</dependency>

If JLatexMath is absent, all strings render as plain text — no exceptions, no warnings.

Licensing

JLatexMath is licensed under GPL v2 + Classpath Exception (exception added in commit f173337 on 2016-01-19). The Classpath Exception permits use as a library from non-GPL code, making it compatible with XChart's Apache 2.0 license.

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Implementation notes

• TexRenderer.java — new central utility; all TeX measurement and painting goes through here
  • isTeX(text) — returns true when JLatexMath is available and string is $...$
  • getBounds() — returns (0, -iconH, iconW, iconH) mimicking TextLayout conventions
  • render() — paints at baseline-equivalent position; 2× supersampling for crispness
  • renderRotated() — for Y-axis titles
• Axis_Y.getYAxisWidthHint() — replaced character-count heuristic with proper per-label width measurement via TexRenderer.getBounds()
• JLatexMath availability detected once via Class.forName() in a static initializer; zero overhead when absent

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Files changed

File	Change
xchart/src/main/java/…/TexRenderer.java	New — central TeX rendering utility
xchart/src/main/java/…/ChartTitle.java	TeX branch in getBoundsHint() and paint()
xchart/src/main/java/…/AxisTitle.java	TeX branch for X and Y axis titles
xchart/src/main/java/…/AxisTickLabels.java	TeX branch for X and Y tick labels
xchart/src/main/java/…/Axis_Y.java	Fixed width-hint measurement for TeX labels
xchart/src/main/java/…/Legend_.java	TeX branch in bounds + paint
pom.xml (root)	jlatexmath in <dependencyManagement> with <optional>true</optional>
xchart/pom.xml	jlatexmath as groupId/artifactId only
xchart-demo/pom.xml	jlatexmath with version (demo app, not optional)
xchart-demo/…/TestForIssue125.java	New — runnable demo
xchart/src/test/…/TexRendererTest.java	New — 10 unit tests
.github/copilot-instructions.md	Added demo run instructions

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Running the demo

mvn install -pl xchart -DskipTests -q && \
mvn compile exec:java -pl xchart-demo \
  -Dexec.mainClass=org.knowm.xchart.standalone.issues.TestForIssue125

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Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.