Shader-Based Image Deformation Effects: Implementation and Principles

This article explores post-processing techniques for image deformation effects using shaders, focusing on three main types of local deformations commonly used in beauty camera applications: twirl effect, inflate effect, and pinch effect. The article explains the fundamental principles behind these effects and provides detailed GLSL shader implementations.

The core concept revolves around constructing deformation functions that take original UV coordinates, deformation position, range, and strength as inputs to generate transformed sampling coordinates. The article introduces a key technique called "sampling distance field transformation" where effects are achieved by manipulating the size and position of sampling circles around a central point.

For the twirl effect, the article explains how to use a decreasing function to relate distance from the center point to rotation angle, creating a vortex-like appearance. The implementation uses either linear equations or smoothstep functions for smoother transitions at boundaries.

The inflate effect is achieved by scaling sampling circles based on distance from the center, using smoothstep functions to create smooth transitions. The strength parameter determines the degree of inflation or shrinkage, with positive values causing inflation and negative values causing shrinkage.

The pinch effect involves translating sampling circles along a specified vector, with the amount of translation decreasing smoothly with distance from the pinch point. This creates the characteristic "pushing" effect where nearby textures are moved toward the pinch endpoint.

The article provides complete GLSL shader code examples for each effect, including dynamic animations using time variables. It also includes links to interactive demonstrations on ShaderToy and references to additional resources for learning more about GLSL transformations and Photoshop's pinch effect algorithm.