再读OpenGL红宝书(1-8章)【续】

原创

phinecos 2021-08-05 14:33:06 博主文章分类：计算机图形学 ©著作权

文章标签 镜面反射光环境光纹理映射 ide 光照模型 文章分类 后端开发

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26）光照模型有4部分：全局环境光，近视点或远视点，双面光照，镜面反射颜色是否和环境颜色，散射颜色分开。要指定全局环境光，可以如下:

GLfloat ambient[] = {0.3,0.3,0.3,1.0};glLightModelfv(GL_LIGHT_MODEL_AMBIENT,ambient);

顶点的镜面反射亮度取决于该点的法线，顶点相对于光源的方向以及顶点相对于视点的方向。要使用近视点，可以这样：glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER,GL_TRUE);这就将视点放置在(0,0,0)处. glLightModelfv(GL_LIGHT_MODEL_TWO_SIDE,GL_TRUE)启用双面光照。典型的光照计算中，分别计算环境光，散射光，镜面反射光和发射光的贡献，然后进行叠加，而在这之后进行纹理映射的话，镜面反射区可能被覆盖，为了解决这个问题，可以glLightModelfv(GL_LIGHT_MODEL_COLOR_CONTROL,GL_SEPARATE_SPECULAR_COLOR); 这样，每个顶点光照计算将产生两种颜色，主颜色和辅助颜色，前者包含所以非镜面反射光照的贡献，后者是所以镜面反射光照的总贡献。纹理映射的时候只将主颜色和纹理颜色混合起来，执行万纹理映射后，再将主颜色和纹理颜色的混合结果与辅助颜色混合起来。

27) 不同材质属性的示例：

void init(void)
{
   GLfloat ambient[] = { 1.0, 0.0, 0.0, 1.0 };
   GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };
   GLfloat specular[] = { 1.0, 1.0, 1.0, 1.0 };
   GLfloat position[] = { 0.0, 3.0, 2.0, 0.0 };
   GLfloat lmodel_ambient[] = { 0.4, 0.4, 0.4, 1.0 };
   GLfloat local_view[] = { 0.0 };

   glClearColor(0.0, 0.1, 0.1, 0.0);
   glEnable(GL_DEPTH_TEST);
   glShadeModel(GL_SMOOTH);

   glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);
   glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
   glLightfv(GL_LIGHT0, GL_POSITION, position);
   glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);
   glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, local_view);

   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
}

void display(void)
{
   GLfloat no_mat[] = { 0.0, 0.0, 0.0, 1.0 };
   GLfloat mat_ambient[] = { 0.7, 0.7, 0.7, 1.0 };
   GLfloat mat_ambient_color[] = { 0.8, 0.8, 0.2, 1.0 };
   GLfloat mat_diffuse[] = { 0.1, 0.5, 0.8, 1.0 };
   GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
   GLfloat no_shininess[] = { 0.0 };
   GLfloat low_shininess[] = { 5.0 };
   GLfloat high_shininess[] = { 100.0 };
   GLfloat mat_emission[] = {0.3, 0.2, 0.2, 0.0};

   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

/*  draw sphere in first row, first column
*  diffuse reflection only; no ambient or specular
*/
   glPushMatrix();
   glTranslatef (-3.75, 3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in first row, second column
*  diffuse and specular reflection; low shininess; no ambient
*/
   glPushMatrix();
   glTranslatef (-1.25, 3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in first row, third column
*  diffuse and specular reflection; high shininess; no ambient
*/
   glPushMatrix();
   glTranslatef (1.25, 3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in first row, fourth column
*  diffuse reflection; emission; no ambient or specular reflection
*/
   glPushMatrix();
   glTranslatef (3.75, 3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in second row, first column
*  ambient and diffuse reflection; no specular
*/
   glPushMatrix();
   glTranslatef (-3.75, 0.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in second row, second column
*  ambient, diffuse and specular reflection; low shininess
*/
   glPushMatrix();
   glTranslatef (-1.25, 0.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in second row, third column
*  ambient, diffuse and specular reflection; high shininess
*/
   glPushMatrix();
   glTranslatef (1.25, 0.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in second row, fourth column
*  ambient and diffuse reflection; emission; no specular
*/
   glPushMatrix();
   glTranslatef (3.75, 0.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in third row, first column
*  colored ambient and diffuse reflection; no specular
*/
   glPushMatrix();
   glTranslatef (-3.75, -3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in third row, second column
*  colored ambient, diffuse and specular reflection; low shininess
*/
   glPushMatrix();
   glTranslatef (-1.25, -3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in third row, third column
*  colored ambient, diffuse and specular reflection; high shininess
*/
   glPushMatrix();
   glTranslatef (1.25, -3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

/*  draw sphere in third row, fourth column
*  colored ambient and diffuse reflection; emission; no specular
*/
   glPushMatrix();
   glTranslatef (3.75, -3.0, 0.0);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
   glutSolidSphere(1.0, 16, 16);
   glPopMatrix();

   glFlush();
}

28）颜色材质模式，

glColorMaterial(GL_FRONT, GL_DIFFUSE);glEnable(GL_COLOR_MATERIAL);这将导致正面的DIFFUSE总是设置为当前颜色

29）混合时，首先指定源因子和目标因子，然后按照公式进行混合（默认的操作是相加），设置因子有两种方式：glBlenFunc()和glBlendFuncSeparate()（它可以指定4个因子，即可以使用不同的方式来混合RGB和alpha值）。除了默认的加法外，还可以使用glBlendEquation()来指定其他的混合方式（如减法等）。

30）启用反走样功能：glEnable(GL_POINT_SMOOTH)或glEnable (GL_LINE_SMOOTH);glEnable (GL_BLEND);或者采用glHint（），例如：

glEnable (GL_LINE_SMOOTH);

glEnable (GL_BLEND);

glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

glHint (GL_LINE_SMOOTH_HINT, GL_DONT_CARE);

31）雾的效果示例：

static GLint fogMode;

/*  Initialize depth buffer, fog, light source,
*  material property, and lighting model.
*/
static void init(void)
{
   GLfloat position[] = { 0.5, 0.5, 3.0, 0.0 };

   glEnable(GL_DEPTH_TEST);

   glLightfv(GL_LIGHT0, GL_POSITION, position);
   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
   {
      GLfloat mat[3] = {0.1745, 0.01175, 0.01175};
      glMaterialfv (GL_FRONT, GL_AMBIENT, mat);
      mat[0] = 0.61424; mat[1] = 0.04136; mat[2] = 0.04136;
      glMaterialfv (GL_FRONT, GL_DIFFUSE, mat);
      mat[0] = 0.727811; mat[1] = 0.626959; mat[2] = 0.626959;
      glMaterialfv (GL_FRONT, GL_SPECULAR, mat);
      glMaterialf (GL_FRONT, GL_SHININESS, 0.6*128.0);
   }

   glEnable(GL_FOG);
   {
      GLfloat fogColor[4] = {0.5, 0.5, 0.5, 1.0};

      fogMode = GL_EXP;
      glFogi (GL_FOG_MODE, fogMode);
      glFogfv (GL_FOG_COLOR, fogColor);
      glFogf (GL_FOG_DENSITY, 0.35);
      glHint (GL_FOG_HINT, GL_DONT_CARE);
      glFogf (GL_FOG_START, 1.0);
      glFogf (GL_FOG_END, 5.0);
   }
   glClearColor(0.5, 0.5, 0.5, 1.0);  /* fog color */
}

static void renderSphere (GLfloat x, GLfloat y, GLfloat z)
{
   glPushMatrix();
   glTranslatef (x, y, z);
   glutSolidSphere(0.4, 16, 16);
   glPopMatrix();
}

/* display() draws 5 spheres at different z positions.
*/
void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   renderSphere (-2., -0.5, -1.0);
   renderSphere (-1., -0.5, -2.0);
   renderSphere (0., -0.5, -3.0);
   renderSphere (1., -0.5, -4.0);
   renderSphere (2., -0.5, -5.0);
   glFlush();
}