Add GPUImageTextureFilter for Lightroom-style mid-frequency texture enhancement

[Copilot]

Implements a texture enhancement filter replicating Adobe Lightroom's Texture slider for adjusting mid-frequency detail in skin, fabric, and surface textures.

Implementation

Core Filter (GPUImageTextureFilter)

• Band-pass filtering via dual Gaussian blurs (1px, 4px radii)
• Custom GLSL shaders for mid-frequency isolation and blending
• Extends GPUImageFilterGroup for efficient GPU composition
• Bidirectional control: negative smooths, positive enhances

Framework Integration

• Added imports to GPUImage.h (iOS/Mac)
• Integrated into FilterShowcase example with slider control

Usage

GPUImageTextureFilter *filter = [[GPUImageTextureFilter alloc] init];
filter.texture = 0.5;  // Range: -1.0 (smooth) to +1.0 (enhance)
[imageSource addTarget:filter];
[filter addTarget:output];

Typical values:

• -0.3: Portrait skin smoothing
• +0.5: Landscape texture enhancement

Technical Details

Filter chain: Input → Blur₁(1px) + Blur₂(4px) → Subtract → Blend(texture) → Output

The band-pass isolates mid-frequency content without affecting fine edges (high-frequency) or overall tone (low-frequency), matching Lightroom's behavior.

Files Requiring Manual Xcode Integration

The following files must be added to GPUImage.xcodeproj:

• framework/Source/GPUImageTextureFilter.h
• framework/Source/GPUImageTextureFilter.m

See XCODE_INTEGRATION.md for detailed instructions.

Original prompt

任务： 添加一个新的特效效果。
描述：给项目添加一个 lightroom 里面的 【Texture】效果、 这个 Texture 效果实际上是提升皮肤纹理细节的。 你需要搜索一下这个效果的具体定义，再编写完善整个代码。

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[Copilot]

Copilot wasn't able to review any files in this pull request.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.