GLSL Programming/Unity

在 Unity 環境下進行 GLSL 開發比起使用編寫獨立的 OpenGL, OpenGL ES 或者 WebGL 應用程序無疑會更為簡單。可以直接導入 mesh，圖片資源（如 Textures）；mipmap 和 normal map 會被自動計算；大部分 GLSL vertex attributes 和 uniforms 變量都是預定義好的，可以直接用；一些 OpenGL 狀態變量可以直接設置。等等。

準備工作

可以在 Unity's download page上下載到免費版本的 Unity，有多種平台版本，Windows，MacOS，Linux等。下面陳述的所有實例都可以在免費版本上實作運行。有幾點需要注意：

• 第一，Windows 用戶啟動 Unity 開發環境時需要傳入如下參數 -force-opengl ，以便可以在 Unity 開發環境中使用 GLSL shader [1]。Windows 默認情況下使用 DirectX。可以參考如下做法避免每次都要從命令終端啟動 Unity ：右鍵單擊 Unity 桌面圖標，編輯屬性選項，例如 "C:\Program Files\Unity\Editor\Unity.exe" -force-opengl（在MacOS 上默認使用的就是 OpenGL）。另外Windows 下還不支持 Web 瀏覽器裡面使用 GLSL shader

• 第二，我們假設讀者朋友們已經熟悉 Unity 開發環境，如果答案是否定的，那麼推薦先閱讀一下 Unity User Guide [2]部分前三節（Unity Basics, Building Scenes, Asset Import and Creation）。

另外，Unity 是支持 GLSL 1.0.x 版本的，也就是 OpenGL ES 2.0（請參考「Khronos OpenGL ES API Registry」），然而 Unity 官方 shader [3]文檔內容主要關注於 Unity 自己的 「Surface Shader」和 Cg/HLSL[4]，僅僅用很少的文字來描述 GLSL 部分[5]。所以這一份 wikibook 也許可以作為 Unity 環境下 GLSL 開發的補充，不過關於優化部分並沒有過多涉及 (請參考這篇博客)。

示例教程

以下示例教程內容具有關聯性，後面的章節一般會依賴於前面的部分，所以請按照順序來閱讀。如果您還沒接觸過 GLSL 或者 Unity，至少應該首先閱讀「Basic」部分！

Basics

• Minimal Shader (關於 着色器,材質,遊戲物體(gameObject))
• RGB Cube (about varyings)
• Debugging of Shaders (about attributes)
• Shading in World Space (about uniforms)

Transparent Surfaces

• Cutaways (about discarding fragments and triangle-face culling)
• Transparency (about blending)
• Order-Independent Transparency (about order-independent blending)
• Silhouette Enhancement (about transforming normal vectors)

Basic Lighting

• Diffuse Reflection (about per-vertex diffuse lighting and multiple light sources of different kinds)
• Specular Highlights (about per-vertex lighting)
• Two-Sided Surfaces (about two-sided per-vertex lighting)
• Smooth Specular Highlights (about per-pixel lighting)
• Two-Sided Smooth Surfaces (about two-sided per-pixel lighting)
• Multiple Lights (about for-loops for handling multiple light sources in one shader pass)

Basic Texturing

• Textured Spheres (about texturing a sphere)
• Lighting Textured Surfaces (about textures for diffuse lighting)
• Glossy Textures (about gloss mapping)
• Transparent Textures (about using alpha textures for discarding fragments, alpha testing, and blending)
• Layers of Textures (about multitexturing)

Textures in 3D

• Lighting of Bumpy Surfaces (about normal mapping)
• Projection of Bumpy Surfaces (about parallax mapping)
• Cookies (about projective texture mapping for shaping light)
• Light Attenuation (about texture mapping for light attenuation and lookup tables in general)
• Projectors (about projective texture mapping for projectors)

Environment Mapping

• Reflecting Surfaces (about reflection mapping)
• Curved Glass (about refraction mapping)
• Skyboxes (about rendering of environment maps as background)
• Many Light Sources (about image-based lighting)

Variations on Lighting

• Brushed Metal (about anisotropic specular reflection)
• Specular Highlights at Silhouettes (about the Fresnel factor for specular reflection)
• Diffuse Reflection of Skylight (about hemisphere lighting)
• Translucent Surfaces (about diffuse and forward-scattered transmission of backlight)
• Translucent Bodies (about diffuse lighting with reduced contrast and transmission of diffuse backlight at silhouettes)
• Soft Shadows of Spheres (about rendering the umbra and penumbra of spheres)
• Toon Shading (about non-photorealistic rendering)

Non-Standard Vertex Transformations

• Screen Overlays (about a direct transformation from object space to screen space)
• Billboards (about view-aligned projection of objects)
• Nonlinear Deformations (about vertex blending)
• Shadows on Planes (about projecting shadows onto planes)
• Mirrors (about mirroring objects and stenciling with the alpha buffer)

Graphics without Shaders

關於 tutorials about graphics programming in Unity without shaders 的一些資料可以在 Cg Programming wikibook 上面找到.

參考鏈接

• Unity shader reference: http://unity3d.com/support/documentation/Components/SL-Reference.html
• Unity shaders in Cg (including built-in shaders): http://www.unifycommunity.com/wiki/index.php?title=Shaders#Unity_3.x_Shaders
• Unity user forum about shaders: http://forum.unity3d.com/forums/16-ShaderLab
• Blog entry about optimizing shaders of iOS: http://aras-p.info/blog/2011/02/01/ios-shader-tricks-or-its-2001-all-over-again/
• Blog entry about a SIGGRAPH presentation on shader optimization: http://blogs.unity3d.com/2011/08/18/fast-mobile-shaders-talk-at-siggraph/
• Utility for analyzing performance of shaders on PowerVR GPUs (e.g. all iOS devices): http://www.imgtec.com/powervr/insider/powervr-pvrshaman.asp