GLSL Programming/Unity

在 Unity 环境下进行 GLSL 开发比起使用编写独立的 OpenGL, OpenGL ES 或者 WebGL 应用程序无疑会更为简单。可以直接导入 mesh，图片资源（如 Textures）；mipmap 和 normal map 会被自动计算；大部分 GLSL vertex attributes 和 uniforms 变量都是预定义好的，可以直接用；一些 OpenGL 状态变量可以直接设置。等等。

准备工作

可以在 Unity's download page上下载到免费版本的 Unity，有多种平台版本，Windows，MacOS，Linux等。下面陈述的所有实例都可以在免费版本上实作运行。有几点需要注意：

• 第一，Windows 用户启动 Unity 开发环境时需要传入如下参数 -force-opengl ，以便可以在 Unity 开发环境中使用 GLSL shader [1]。Windows 默认情况下使用 DirectX。可以参考如下做法避免每次都要从命令终端启动 Unity ：右键单击 Unity 桌面图标，编辑属性选项，例如 "C:\Program Files\Unity\Editor\Unity.exe" -force-opengl（在MacOS 上默认使用的就是 OpenGL）。另外Windows 下还不支持 Web 浏览器里面使用 GLSL shader

• 第二，我们假设读者朋友们已经熟悉 Unity 开发环境，如果答案是否定的，那么推荐先阅读一下 Unity User Guide [2]部分前三节（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（请参考“Khronos OpenGL ES API Registry”），然而 Unity 官方 shader [3]文档内容主要关注于 Unity 自己的 “Surface Shader”和 Cg/HLSL[4]，仅仅用很少的文字来描述 GLSL 部分[5]。所以这一份 wikibook 也许可以作为 Unity 环境下 GLSL 开发的补充，不过关于优化部分并没有过多涉及 (请参考这篇博客)。

示例教程

以下示例教程内容具有关联性，后面的章节一般会依赖于前面的部分，所以请按照顺序来阅读。如果您还没接触过 GLSL 或者 Unity，至少应该首先阅读“Basic”部分！

Basics

• Minimal Shader (关于 着色器,材质,游戏物体(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

关于 tutorials about graphics programming in Unity without shaders 的一些资料可以在 Cg Programming wikibook 上面找到.

参考链接

• 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