TouchGFX vs. LVGL vs. Qt: Choosing the Right HMI for Your Embedded Device

Selecting the appropriate GUI framework for embedded devices requires evaluating technical capabilities, resource requirements, and development workflows. This article provides an objective comparison of TouchGFX, LVGL, and Qt for MCUs to help engineers make informed decisions based on project requirements.

Core Technical Capabilities

TouchGFX

TouchGFX excels in performance optimization for STM32 microcontrollers. The framework leverages hardware acceleration through the Chrom-ART engine, enabling smooth 60 FPS animations on mid-range MCUs. Written in C++, TouchGFX employs a retained mode rendering model with efficient dirty rectangle tracking to minimize redraw operations.

The memory management system uses predominantly static allocation, preventing fragmentation but requiring careful planning of screen transitions. Text rendering occurs at compile-time by default, converting strings to bitmaps for optimal runtime performance. This approach enhances speed but complicates dynamic text changes and internationalization.

TouchGFX Designer provides a visual development environment that generates C++ code, offering significant productivity advantages for teams with designers and developers. The workflow integrates well with STM32CubeMX, streamlining the initial project setup process.

LVGL

LVGL prioritizes resource efficiency and platform independence. Written in C with an object-oriented architecture, it functions on virtually any hardware with a display, including 8-bit microcontrollers. The framework requires as little as 32KB flash and 16KB RAM while still providing a comprehensive feature set.

The rendering system supports multiple buffer strategies (full, partial, double) that can be selected based on available memory and performance requirements. Unlike TouchGFX's compile-time approach, LVGL renders text at runtime with optional caching, offering more flexibility for dynamic content and language switching.

LVGL implements a signal propagation system for event handling, allowing events to flow through the object hierarchy. This enables sophisticated interactions but requires proper understanding of propagation rules. Configuration options span multiple header files, requiring attention to ensure consistent settings across the application.

Qt for MCUs

Qt for MCUs adapts the established Qt framework specifically for microcontroller environments. Unlike its larger counterpart, it's built from the ground up for resource-constrained devices, though it still requires more substantial hardware than the alternatives—typically Cortex-M7 class processors with at least 256KB RAM.

The framework's distinctive feature is QML, a declarative language for interface design paired with JavaScript for logic. Importantly, Qt for MCUs pre-compiles QML to C++ during build time rather than interpreting it at runtime, addressing performance concerns on microcontrollers. The signal/slot mechanism familiar to Qt developers has been reimplemented with a lightweight design optimized for MCUs.

Qt for MCUs functions effectively without OpenGL ES but can leverage hardware acceleration when available. The comprehensive development toolchain includes Qt Design Studio for visual interface creation and debugging capabilities.

Development Experience

The development experience varies significantly between frameworks, affecting both productivity and maintainability.

TouchGFX development revolves around its Designer tool, which provides a visual canvas for interface creation. While this accelerates initial development, regenerating code can potentially overwrite custom modifications unless developers carefully use protected regions. The framework's tight coupling with STM32 hardware simplifies development for these platforms but introduces complexity when porting to other architectures.

LVGL development typically involves directly coding the interface using its C API, though the commercial SquareLine Studio offers visual design capabilities. The direct coding approach provides maximum control but may require more time for interface implementation. The object hierarchy significantly impacts both event handling and memory usage, requiring thoughtful interface design.

Qt for MCUs leverages established Qt workflows, allowing teams with Qt experience to transfer their knowledge. Development involves either Qt Design Studio for visual design or direct QML coding. The framework requires solid C++ skills, particularly for debugging and extension. The commercial license includes professional support but adds to project costs.

Technical Implementation Considerations

Each framework presents unique technical considerations that can significantly impact project success.

TouchGFX contains hardware-specific optimizations including hand-tuned assembly for certain STM32 variants. These optimizations deliver excellent performance on supported hardware but don't translate directly to different architectures. The partial screen redraw mechanism requires proper understanding of invalidation to avoid visual artifacts during complex animations.

LVGL's buffer strategy selection dramatically affects both performance and memory usage. Full-frame buffering provides the best visual quality but requires substantial RAM, while partial buffering reduces memory requirements at the potential cost of visual artifacts. Memory fragmentation can occur with dynamic UI elements, potentially requiring custom allocation strategies for long-running applications.

Qt for MCUs addresses many challenges of traditional Qt through purpose-built optimizations. The streamlined architecture eliminates much of the overhead associated with full Qt while maintaining the framework's component model. Despite these improvements, Qt for MCUs still requires more substantial hardware resources than either TouchGFX or LVGL.

Framework Selection Guide

The optimal framework choice depends on specific project requirements and constraints:

Hardware Considerations

For STM32-based projects, TouchGFX offers significant advantages through hardware-specific optimizations and deep integration with ST's ecosystem. The framework maximizes performance on these platforms and provides a smooth development experience when staying within the ST environment.

When targeting extremely resource-constrained systems or requiring hardware independence, LVGL provides the most flexibility. Its minimal requirements and platform-agnostic approach make it suitable for a wide range of MCUs from 8-bit architectures to powerful application processors.

Projects using higher-end microcontrollers (Cortex-M7 or better) with substantial memory resources can benefit from Qt for MCUs' comprehensive capabilities. The framework is particularly well-suited for complex applications that require sophisticated UI components and extensive middleware.

Development Team Factors

Teams with designers and developers working collaboratively will benefit from TouchGFX's visual design tools and code generation capabilities. The designer-friendly workflow reduces the communication overhead between UI designers and embedded developers.

For teams with strong C programming skills but limited C++ experience, LVGL provides a familiar development model with its C-based API. The object-oriented architecture offers many modern programming benefits without requiring extensive C++ knowledge.

Organizations with existing Qt expertise can leverage this knowledge when using Qt for MCUs. The familiar programming model and tooling reduce the learning curve despite the differences between desktop Qt and its MCU-focused variant.

Project Requirements

Applications requiring maximum performance on mid-range hardware, particularly STM32 microcontrollers, are well-served by TouchGFX. Its hardware-acceleration capabilities and optimized rendering make it ideal for animation-heavy interfaces on constrained hardware.

Projects prioritizing portability across diverse hardware platforms benefit from LVGL's hardware-independent design. The framework's flexible configuration options allow it to adapt to various display technologies and processing capabilities.

Complex applications requiring sophisticated UI components, state management, and middleware integration are natural candidates for Qt for MCUs. Its comprehensive feature set and component model simplify the development of advanced interfaces.

Commercial Considerations

The frameworks differ significantly in their licensing and commercial support models:

TouchGFX is free for use with STM32 microcontrollers following ST's acquisition of the framework. This eliminates licensing costs for projects targeting these platforms, though porting to other architectures may involve additional considerations.

LVGL is available under the MIT license, allowing use in both commercial and non-commercial applications without royalty fees. This permissive licensing provides maximum flexibility for various project types and business models.

Qt for MCUs requires commercial licensing for most production use cases. While this adds to project costs, it includes professional support and indemnification that may be valuable for commercial products, particularly in regulated industries.

Conclusion

Each framework offers distinct advantages for specific use cases:

• TouchGFX provides optimized performance for STM32 microcontrollers with designer-friendly tools, making it ideal for STM32-based projects with significant UI requirements.

• LVGL offers maximum flexibility with minimal resource requirements and open-source licensing, excelling in resource-constrained or hardware-independent applications.

• Qt for MCUs delivers a comprehensive solution for higher-end embedded systems, benefiting complex applications on more powerful microcontrollers.

The optimal selection depends on systematically evaluating hardware capabilities, team expertise, and project requirements rather than subjective preferences. By matching these factors to each framework's strengths, engineering teams can select the most appropriate tool for their embedded HMI development.