Unicode and LaTeX Support in fortplot

Overview

fortplot provides comprehensive support for Unicode characters and LaTeX-style Greek letter commands across all backends (PNG, PDF, ASCII). This enables professional scientific plotting with mathematical notation directly from Fortran code.

Features

LaTeX-Style Greek Letters

All 24 Greek letters are supported in both uppercase and lowercase forms:

Lowercase Greek Letters

• \alpha → α, \beta → β, \gamma → γ, \delta → δ
• \epsilon → ε, \zeta → ζ, \eta → η, \theta → θ
• \iota → ι, \kappa → κ, \lambda → λ, \mu → μ
• \nu → ν, \xi → ξ, \omicron → ο, \pi → π
• \rho → ρ, \sigma → σ, \tau → τ, \upsilon → υ
• \phi → φ, \chi → χ, \psi → ψ, \omega → ω

Uppercase Greek Letters

• \Alpha → Α, \Beta → Β, \Gamma → Γ, \Delta → Δ
• \Epsilon → Ε, \Zeta → Ζ, \Eta → Η, \Theta → Θ
• \Iota → Ι, \Kappa → Κ, \Lambda → Λ, \Mu → Μ
• \Nu → Ν, \Xi → Ξ, \Omicron → Ο, \Pi → Π
• \Rho → Ρ, \Sigma → Σ, \Tau → Τ, \Upsilon → Υ
• \Phi → Φ, \Chi → Χ, \Psi → Ψ, \Omega → Ω

Backend-Specific Rendering

ASCII Backend

• Renders actual Unicode characters in terminal output
• Compatible with modern terminals that support UTF-8
• Fallback handling for unsupported characters

PNG Backend

• High-quality antialiased Unicode rendering via STB TrueType
• Professional font rendering with proper spacing
• Supports all Unicode characters available in system fonts

PDF Backend

• Vector Unicode characters for scalable, professional output
• Embedded in PDF for universal compatibility
• Maintains crisp rendering at any zoom level

Usage Examples

Basic Usage

use fortplot
type(figure_t) :: fig

call fig%initialize()
call fig%set_title("Schrödinger Equation: i\hbar\partial\psi/\partial t = H\psi")
call fig%set_xlabel("Position \xi")
call fig%set_ylabel("Wavefunction \Psi(\xi)")
call fig%add_plot(x, psi_real, label="Re[\psi]")
call fig%add_plot(x, psi_imag, label="Im[\psi]")
call fig%legend()

! Works with all backends
call fig%savefig("schrodinger.png")  ! PNG with Unicode
call fig%savefig("schrodinger.pdf")  ! PDF with Unicode
call fig%savefig("schrodinger.txt")  ! ASCII with Unicode

Common Mathematical Expressions

! Wave equations
call fig%set_title("Wave: \psi = A e^{i(\omega t - kx)}")

! Thermodynamics
call fig%set_xlabel("Temperature T (K)")
call fig%set_ylabel("Entropy \Delta S")

! Electromagnetic fields
call fig%add_plot(time, electric_field, label="E-field: \epsilon E")
call fig%add_plot(time, magnetic_field, label="B-field: \mu B")

! Statistical mechanics
call fig%set_title("Distribution: P(\xi) = e^{-\beta H(\xi)}/Z")

Complex Mathematical Notation

! Maxwell's equations
call fig%set_title("Maxwell: \nabla \times E = -\partial B/\partial t")

! Quantum mechanics
call fig%set_xlabel("Momentum p = \hbar k")
call fig%set_ylabel("Energy E = \hbar \omega")

! Statistical physics
call fig%add_plot(temp, entropy, label="S = k_B ln(\Omega)")

Implementation Details

Text Processing Pipeline

1. LaTeX Recognition: Identifies \command patterns in text
2. Command Validation: Checks against supported Greek letter commands
3. Unicode Conversion: Maps LaTeX commands to Unicode codepoints
4. UTF-8 Encoding: Converts Unicode codepoints to UTF-8 byte sequences
5. Backend Rendering: Renders Unicode characters using backend-specific methods

Architecture

The Unicode support is implemented through several modules:

• fortplot_latex_parser: LaTeX command recognition and parsing
• fortplot_unicode: Unicode detection and UTF-8 handling
• Backend Integration: Unified text processing across all backends

Performance Considerations

• LaTeX processing is performed at render time, not during plot data operations
• Unicode conversion uses efficient lookup tables
• Minimal overhead for text without LaTeX commands
• Font rendering leverages optimized STB TrueType library

Limitations and Known Issues

Supported Commands

• Currently supports Greek letters only
• Mathematical operators (\nabla, \partial, etc.) are preserved as-is
• Subscripts and superscripts are not yet supported

Font Dependencies

• PNG/PDF backends require system fonts with Unicode support
• ASCII backend depends on terminal UTF-8 support
• Fallback to ASCII representation when Unicode is unavailable

Character Encoding

• Input text should be UTF-8 compatible
• Mixed encoding may produce unexpected results

Testing

Comprehensive test coverage includes:

• All 24 Greek letters (uppercase and lowercase)
• Edge cases: empty strings, invalid commands, mixed content
• Cross-backend compatibility testing
• Unicode character validation
• LaTeX command parsing accuracy

Run Unicode tests:

make test ARGS="--target test_comprehensive_unicode_coverage"
make test ARGS="--target test_unicode_png_pdf_rendering"
make test ARGS="--target test_unicode_ascii_rendering_simple"

Examples

See the complete working example:

make example ARGS="unicode_demo"

This generates demonstration plots showing Unicode rendering across all backends with comprehensive mathematical notation examples.

Future Enhancements

Potential future additions: - Mathematical operators (\nabla, \partial, \int, etc.) - Subscripts and superscripts - Additional symbol sets (arrows, operators, etc.) - LaTeX math mode parsing - Custom symbol definitions