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第二课

第二课. Lighting enabled. Lighting disabled. Overview of this Section. Lighting ( 光照 ) & Material ( 材质 ) OpenGL Implementation. Lighting. Simple illumination 简单光照模型 简单光照模型是经验模型 计算量相对较小，适合实时绘制要求 OpenGL 、 Direct3D 直接支持 Local illumination 局部光照模型 BRDF( 双向反射分布函数 ) 等

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第二课

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  1. 第二课

  2. Lighting enabled Lighting disabled Overview of this Section • Lighting (光照) & Material (材质) • OpenGL Implementation

  3. Lighting • Simple illumination 简单光照模型 • 简单光照模型是经验模型 • 计算量相对较小，适合实时绘制要求 • OpenGL、Direct3D直接支持 • Local illumination 局部光照模型 • BRDF(双向反射分布函数)等 • Global illumination 整体光照模型 • 光线跟踪、辐射度等

  4. Simple Illumination • Reflection, Transmission, Absorption • Reflection • Specular Reflection （镜面反射） • Diffuse Reflection (漫反射) • Phong 模型 • 理想漫反射 + 镜面反射 + 环境光

  5. Phong • Diffuse （理想漫反射） • View Independent （视点无关） • Id = IpKd*(L∙N) • Specular (镜面反射) • View Dependent (视点相关) • Is = IpKs(R∙V)n • Ambient (环境光) • 均匀分布 • Ie = IaKa

  6. Phong • I = IaKa + IpKs(R∙V)n + IpKd*(L∙N) • 实际计算中 • H∙N替代R∙V • H为L和V的平分向量

  7. Phong • 第一个有影响的光照模型，视觉效果接近真实 • 缺乏质感、存在部分失真等

  8. Gourand & Phong 明暗处理 • 同一多边形内部法向一致，颜色相同 • 不同多边形邻接处有明显光强突变 • 双线性光强插值 Gourand明暗处理 • 双线性法向插值 Phong明暗处理

  9. Gourand明暗处理 • 计算多边形顶点平均法向 • Phong模型计算顶点光强 • 插值计算边上的各点光强 • 插值计算多边形内部各点光强

  10. Phong明暗处理 • 计算多边形顶点平均法向 • 插值离散边上各点法向 • 插值多边形内部法向 • 计算各像素光强度

  11. 插值效果 • Gourand插值计算量小，但会影响高光效果绘制 • Phong插值计算量大，真实感更高

  12. Light in OpenGL • Ambient Color • 光源的环境光，一般为 零 • Diffuse Color • 可被认为是光源的颜色 • Specular Color • 一般与Diffuse颜色相当

  13. Light Ambient : Green Diffuse : Red Specular : Blue

  14. Material in OpenGL • Material • 描述对入射光的反射系数 • Diffuse • 描述物体颜色最重要的参数 • Ambient • 受全局环境光以及各光源环境光影响

  15. Material in OpenGL • Specular & Shininess • Shininess控制高光的程度 • Emission • 使物体看上去像是在发光，但实际上并不等于光源，一般用来模拟光源

  16. OpenGL Lighting • 顶点颜色计算模型 • Emission + Global Light Ambient * Material Ambient + ∑(Lighti Ambient * Material Ambient + Lighti Specular * Material Specular + Lighti Diffuse * Material Diffuse) • 材质自发光属性 并不等于光源

  17. Put Light into OpenGL • 绘制步骤 • 为每个物体顶点设定法向 • 创建光源，并设定位置 • 创建和选择光照模型 • 设置物体材质属性

  18. Assign Normal Vector • 设定顶点法向 • glNormal{34}{isfd}[v](TYPE* normal); • Assign normal vector for vertices (the normal vector should be assigned before you assign vertices). • Normal vectors must be normalize. OpenGL can automatically normalize normal vector by glEnable(GL_NORMALIZE);

  19. Sample： Assign Normal Vector glBegin(GL_TRIANGLE); glNormal3f(0.0, 1.0, 0.0); glVertex3f(1.0, 0.0, 0.0); glVertex3f(0.0, 0.0, -1.0); glVertex3f(-1.0, 0.0, 0.0); glEnd();

  20. Light Source • 启用并设置光源参数 • Use glEnable(GL_LIGHT0); to enable light zero. You can use at most 8 light sources in OpenGL spec. (GL_LIGHT0~GL_LIGHT7) • glLight{if}[v](GLenum light, Glenum pname, TYPE param); • Specify the attribute of light • light can be GL_LIGHT0 ~ GL_LIGHT7 • pname is the characteristic of the light • param is the value of pname

  21. Pname Def. Value Meaning GL_AMBIENT (0.0, 0.0, 0.0, 0.0) 环境光颜色 GL_DIFFUSE (1.0, 1.0, 1.0, 1.0) 散射光颜色 GL_SPECULAR (1.0, 1.0, 1.0, 1.0) 镜面反射光颜色 GL_POSITION (0.0, 0.0, 1.0, 0.0) 位置坐标 GL_SPOT_DIRECTION (0.0, 0.0, -1.0) 指定聚光灯方向 GL_SPOT_EXPONENT 0.0 聚光指数 GL_SPOT_CUTOFF 180.0 spotlight cutoff angle GL_CONSTANT_ATTENUATION 1.0 constant attenuation factor GL_LINEAR_ATTENUATION 0.0 linear attenuation factor GL_QUADRATIC_ATTENUATION 0.0 quadratic attenuation factor Light Source

  22. Light Source • Color • The default values listed for GL_DIFFUSE and GL_SPECULAR apply only to GL_LIGHT0. • For other lights, the default value is (0.0, 0.0, 0.0, 1.0 ) for both GL_DIFFUSE and GL_SPECULAR. • Ex. • GLfloat light_ambient[4] = {0.0, 0.0, 1.0, 0.0}; • glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient); • Position ( x, y, z, w ) • W is ZERO, Directional light, (x,y,z) specify its direction. • W is NONZERO, Positional light, (x,y,z) specify the location of the light source. • ModelView Enabled

  23. Light Source • Attenuation (衰减系数) • d = 光源到顶点位置 • kc = GL_CONSTANT_ATTENUATION • kl = GL_LINEAR_ATTENUATION • kq = GL_QUADRATIC_ATTENUATION • 方向光源，Attenuation is 1

  24. Material • Define material properties for objects in the scene. • void glMaterial{if}[v](GLenum face, GLenum pname, TYPE[*] param); • Specifies a current material property for use in lighting calculations.

  25. Pname Def. Value Meaning GL_AMBIENT (0.2, 0.2, 0.2, 1.0) ambient color of material GL_DIFFUSE (0.8, 0.8, 0.8, 1.0) diffuse color of material GL_AMBIENT_AND_DIFFUSE ambient and diffuse color of material GL_SPECULAR (0.0, 0.0, 0.0, 1.0) specular color of material GL_SHININESS 0.0 specular exponent GL_EMISSION (0.0, 0.0, 0.0, 1.0) emissive color of material GL_COLOR_INDEXES (0, 1, 1) ambient, diffuse, and specular color indices Material

  26. No Ambient Gray Ambient Blue Ambient Diffuse Only Specular Higher Shininess Emission Material

  27. Light • Demo, Light Position • Demo, Light Material

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