Why a designer built an app instead of a mockup

Using AI in the design process allows designers to create actually working mockups themselves, dramatically reducing communication costs with developers. Toss's underlay project was planned to turn the 'dead end' where a user's experience ends into the starting point of the next experience.

Instead of the existing overlay approach used by bottom sheets or toasts, which appear floating on top of the screen, the project adopted an underlay approach in which something that already existed beneath the screen is revealed. This aims to naturally convey information without interrupting the user's actions.

The designer chose SwiftUI and Xcode instead of interaction tools. Despite having no proficiency in Protopie or Framer, they completed the work using AI to perform the following roles:

• Explaining the direction of the interaction they wanted to experience
• Selecting the best result among the code AI suggested
• Checking and judging the results on an actual device

In particular, to implement a scan effect where light sweeps across the screen, they directly adjusted Metal shader code, completing a design centered on actual movement (interaction) rather than a static screen.