Turning Apple Pencil Into a Reed Pen: How I Built and Shipped Qalaris
How I built Qalaris: an iPad app that turns Apple Pencil into a digital reed pen for Arabic calligraphy, with multimodal AI review and RevenueCat.
Qalaris is an iPad app developed by RevenueCat and shipped in 2026. It simulates a reed pen using an Apple Pencil, offering guided Arabic calligraphy lessons, multimodal AI review, and a credit system built with RevenueCat. The project aimed to bridge Arabic calligraphy, a cultural tradition inscribed by UNESCO in 2021, to a wider audience with iPads and Apple Pencils.
The core challenge was to mimic the behavior of a reed pen, which differs significantly from a digital brush. A reed pen's flat-cut nib creates varying marks based on movement direction and angle, with ink supply being finite. This forced Qalaris to simulate these physical constraints, unlike typical digital brushes.
Qalaris uses Apple Pencil data such as azimuth, force, and altitude to render the strokes. It maps these signals into nib orientation and width, constrained to mimic a reed pen's behavior. Freehand mode allows responsive rotation, while guided lessons lock the nib to specific angles. The app also features an ink supply that declines as strokes are drawn, requiring refills from a virtual inkwell.
The development process involved nearly 50 video iterations with multimodal model Gemini. Gemini analyzed the rendered engine, suggested revisions, and generated new Swift code based on user feedback, creating an iterative loop of development. This approach allowed for real-time adjustments to the drawing engine's behavior, ensuring the final product accurately simulated a reed pen's experience.
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