OpenGL学习十八:多重细节层

在动态场景中，当一个纹理对象迅速地远离观察点时，纹理图像必须随着背投影的图像一起缩小，为了实现这个效果，OPENGL必须对纹理图像进行过渡，适当地对它进行缩小，使他不会产生令人不舒服的视觉感受。
OpenGL mipmap 预先设置好不同分辨率的纹理图像，根据被贴图的物体的大小确定采用哪种分辨率的纹理图像，达到平滑过渡的效果

 

使用mipmap必须提供全系列的大小为2的整数次方的纹理图像，其范围从最大值直到1*1，例如最大值为64*16的纹理单元还必须提供32*8，16*4,8*2,4*1，2*1,1*1的纹理单元。他们的分辨率为，0,1,2,3,4,5,6
另外使用mipmap还需要选择一种适当的过滤模式
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER， GL_NEAREST_MIPMAP_NEAREST)

 

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);//黄
glTexImage2D(GL_TEXTURE_2D, 1, GL_RGBA, 16, 16, 0,GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage16);//紫
glTexImage2D(GL_TEXTURE_2D, 2, GL_RGBA, 8, 8, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage8);//红
glTexImage2D(GL_TEXTURE_2D, 3, GL_RGBA, 4, 4, 0,GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage4);//绿
glTexImage2D(GL_TEXTURE_2D, 4, GL_RGBA, 2, 2, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage2);//蓝
glTexImage2D(GL_TEXTURE_2D, 5, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage1);//白

 

 

mipmap层控制

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);//最高分辨率层
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 4);//最低分辨率层

mipmap细节层参数控制  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_LOD, 1);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 3);

对于32*32的纹理图像来说，包含16*16,8*8,4*4,2*2,1*1. min可以简单的认为是起始分辨率（最大值） max是结束分别率（最大值）

 

上面方法如果要创建一个64*16的纹理，必须创建7个纹理图形，并进行分别绑定，很繁琐，当然OpenGL提供了一些方法，让这一切变得简单
 方法1：OPENGL 1.4 以后
 glTexParameteri(GL_TEXTURE_2D,GL_GENERATE_MIPMAP,GL_TRUE);
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);

方法2： OPENGL1.1
 gluBuild2DMipmaps(GL_TEXTURE_2D,  GL_RGBA, 32, 32, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);

方法3：OPENGL3.0
glGenerateMipmap(GL_TEXTURE_2D)
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);

 

#include "header.h"

GLubyte mipmapImage32[32][32][4];
GLubyte mipmapImage16[16][16][4];
GLubyte mipmapImage8[8][8][4];
GLubyte mipmapImage4[4][4][4];
GLubyte mipmapImage2[2][2][4];
GLubyte mipmapImage1[1][1][4];

#ifdef GL_VERSION_1_1
static GLuint texName;
#endif

void makeImages(void)
{
   int i, j;
    
   for (i = 0; i < 32; i++) {
      for (j = 0; j < 32; j++) {
         mipmapImage32[i][j][0] = 255;
         mipmapImage32[i][j][1] = 255;
         mipmapImage32[i][j][2] = 0;
         mipmapImage32[i][j][3] = 255;
      }
   }
   for (i = 0; i < 16; i++) {
      for (j = 0; j < 16; j++) {
         mipmapImage16[i][j][0] = 255;
         mipmapImage16[i][j][1] = 0;
         mipmapImage16[i][j][2] = 255;
         mipmapImage16[i][j][3] = 255;
      }
   }
   for (i = 0; i < 8; i++) {
      for (j = 0; j < 8; j++) {
         mipmapImage8[i][j][0] = 255;
         mipmapImage8[i][j][1] = 0;
         mipmapImage8[i][j][2] = 0;
         mipmapImage8[i][j][3] = 255;
      }
   }
   for (i = 0; i < 4; i++) {
      for (j = 0; j < 4; j++) {
         mipmapImage4[i][j][0] = 0;
         mipmapImage4[i][j][1] = 255;
         mipmapImage4[i][j][2] = 0;
         mipmapImage4[i][j][3] = 255;
      }
   }
   for (i = 0; i < 2; i++) {
      for (j = 0; j < 2; j++) {
         mipmapImage2[i][j][0] = 0;
         mipmapImage2[i][j][1] = 0;
         mipmapImage2[i][j][2] = 255;
         mipmapImage2[i][j][3] = 255;
      }
   }
   mipmapImage1[0][0][0] = 255;
   mipmapImage1[0][0][1] = 255;
   mipmapImage1[0][0][2] = 255;
   mipmapImage1[0][0][3] = 255;
}
   int a;
      GLboolean b=0;
void init(void)
{    
   glEnable(GL_DEPTH_TEST);
   glShadeModel(GL_FLAT);

   glTranslatef(0.0, 0.0, -3.6);
   makeImages();
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

#ifdef GL_VERSION_1_1
   glGenTextures(1, &texName);
   glBindTexture(GL_TEXTURE_2D, texName);
#endif
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, 
                   GL_NEAREST_MIPMAP_NEAREST);
   //方法3：
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);
   glTexImage2D(GL_TEXTURE_2D, 1, GL_RGBA, 16, 16, 0,
	   GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage16);
   glTexImage2D(GL_TEXTURE_2D, 2, GL_RGBA, 8, 8, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage8);
   glTexImage2D(GL_TEXTURE_2D, 3, GL_RGBA, 4, 4, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage4);
   glTexImage2D(GL_TEXTURE_2D, 4, GL_RGBA, 2, 2, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage2);
   glTexImage2D(GL_TEXTURE_2D, 5, GL_RGBA, 1, 1, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage1);

   // glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
	//glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 4);
  // 方法1：OPENGL 1.4 以后
	/*glTexParameteri(GL_TEXTURE_2D,GL_GENERATE_MIPMAP,GL_TRUE);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);*/

  // 方法2： OPENGL1.1
	   //gluBuild2DMipmaps(GL_TEXTURE_2D,  GL_RGBA, 32, 32, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);

   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_LOD, 1);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 4);

   glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
   glEnable(GL_TEXTURE_2D);

   //glGetTexLevelParameteriv(GL_TEXTURE_RESIDENT,0,texName,&a);

   glAreTexturesResident(1,&texName,&b);

     glEnable(GL_TEXTURE_2D);
}

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
#ifdef GL_VERSION_1_1
   glBindTexture(GL_TEXTURE_2D, texName);
#endif
   glBegin(GL_QUADS);
   glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
   glTexCoord2f(0.0, 8.0); glVertex3f(-2.0, 1.0, 0.0);
   glTexCoord2f(8.0, 8.0); glVertex3f(2000.0, 1.0, -6000.0);
   glTexCoord2f(8.0, 0.0); glVertex3f(2000.0, -1.0, -6000.0);
   glEnd();
   glFlush();
}

void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 30000.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (50, 50);
   glutCreateWindow (argv[0]);
   glewInit();
   init ();
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;     
}