实现逐顶点的ambient,diffuse,andspecularshadingphong光照模型

1、实现逐顶点的ambient, diffuse, and specular (ADS) shadingphong 光照模型本文参照了OpenGL 4.0 Shading Language CookbookOpenGL 4.0 渲染管线如图： 1. shader 数据的输入可以是从OpenGL main application中输入或者是来自上个渲染管线，例如一个fragment shader 的输入可能来自vertexshader 的 output 变量也可能来自程序的uniform变量。2. 每个顶点会执行一次 vertex shader （ 通常是并行进行） 。3. 顶点位置在 vertex

2、 shader 中必须被转换到裁剪坐标系(clip coordinates)并赋值给gl_position变量。4.在vertexshader和fragmentshader 之间的渲染管线中，顶点被装配成片元(primiteves)、然后裁切(clipping)、应用viewporttransformation、然后进行光栅化和填充多边形 （如果需要的话）。每个多边形的片元 fragment或 (像素 pixel) 会执行一次fragment shader（通常是并行）- （ The fragmentshader is executed once for each fragment (pixe

3、l) of the polygonbeing rendered (typically in parallel).5. 来自vertex shader的数据默认情况下是 通过插值以透视的方式提供给fragment shader 然后 fragment shader 确定 最终像素的颜色 并发送给 frame buffer 。6. 深度值信息被自动处理 Implementing per-vertex ambient,diffuse, and specular (ADS)shadingOpenGL 固定的渲染管线实现了一个默认的光照系统（和本文的Ads 模型类似）它综合了环境光Ambient、漫反射

4、 Diffuse 、镜面光 Specular。The ambient component is intended to model light that has been reflected so many times that it appears to be emanating uniformly （均匀地 散发） fromall directionsThe diffuse component wasomnidirectional（全方位的） reflectionrepresents 见用单光源实现逐顶点漫反射光照模型The specular component models the sh

5、ininess of the surface and represents reflection around a preferred directionCombining these three components together can model a nice (but limited) variety of surface types. This shading model is also sometimes called thePhong reflection model (or Phong shading model), after Bui Tuong Phong 如下图的 A

6、DS 光照模型 ADS 光照模型的总强度是 Ambient 、Diffuse 、和 Specular 的光照强度总和。 The ambient component represents light that illuminates all surfaces equally and reflects equally in all directions 。 It is often used to help brighten some of the darker areas within a scene。由于环境光 (Ambient ）不受入射光和出射光的影响，因此可以简单的用光源光照密度(La)

7、和物体便面的反射系数(Ka)Diffuse 光照模型镜面反射模型：计算反射光的公式：要对镜面反射（Specular）建模，需要这几个向量（都是单位化的），从物体表面到光源的方向向量（ S），理想反射光方向向量（ r) ，朝向 viewer 的方向向量（ V ），和物体表面的法线向量 （n),如下图显示 We would like the reflection to be maximal when the viewer is aligned with the vector r, and to fall off quickly as the viewer moves furtheraway fro

8、m alignment with r. This can be modeled using the cosine of the angle between v and r raised to some power(f).The specular component creates specular highlights (bright spots) that are typical of glossy surfaces. The larger the power of f in the equation, the smaller the specular highlight and the s

9、hinier the surface appears. The value for f is typically chosen to be somewhere between 1 and 200.最后，最终的 ADS 光照模型公式如下顶点 shadercpp view plain copy print?#version430layout (location = 0) in vec3 VertexPosition;layout(location = 1) in vec3 VertexNormal;out vec3LightIntensity;struct LightInfo vec4 Posit

10、ion; / Lightposition in eye coords.vec3 La;/ Ambient lightintensityvec3 Ld;/ Diffuse light intensityvec3Ls;/ Specular light intensity; uniform LightInfoLight;struct MaterialInfo vec3 Ka;/Ambient reflectivityvec3 Kd;/ Diffusereflectivityvec3 Ks;/ Specular reflectivityfloat Shininess;/ Specular shinin

11、ess factor ; uniformMaterialInfo Material;uniform mat4 ModelViewMatrix;uniform mat3 NormalMatrix;uniform mat4 ProjectionMatrix;uniform mat4 MVP;void main()vec3 tnorm =normalize( NormalMatrix * VertexNormal);vec4eyeCoords = ModelViewMatrix * vec4(VertexPosition,1.0);vec3 s = normalize(vec3(Light.Posi

12、tion - eyeCoords);vec3 v = normalize(-eyeCoords.xyz);vec3 r = reflect( -s,tnorm );float sDotN = max( dot(s,tnorm), 0.0 );vec3 ambient = Light.La * Material.Ka;vec3 diffuse =Light.Ld * Material.Kd * sDotN;vec3 spec = vec3(0.0);if( sDotN > 0.0 )spec = Light.Ls * Material.Ks *pow( max( dot(r,v), 0.0 ), Material.Shininess );LightIntensity = ambient + diffuse + spec;gl_Position