各向异性纹理过滤,各向异性过滤ppsspp

如果使用一般的纹理过滤，当观察方向跟模型表面不是相互垂直的的情况下，会出现纹理信息的丢失，表现为图像看上去比较模糊，如下图所示，远处场景的细节信息很差：

针对这种情况，可以采用同向异性过滤的方式处理纹理，在过滤纹理的时候，考虑到观察角度不同，使纹理本身沿着模型表面倾斜的方向进行延伸。

使用如下语句查询当前系统支持的最大同向异性过滤的数值，数值越大，表示沿着最大变化方向所采样的纹理单元越多，显示效果就越好：

GLfloat max_TexAni; //查询允许的各向异性数量glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &max_TexAni);

以“ GL_TEXTURE_MAX_ANISOTROPY_EXT ”为参数调用“ glTexParameterf ”函数，并设置同向异性过滤的数值，就可以使设置生效。以下是经过同向异性过滤设置的显示效果：

远处纹理的细节增强了很多。以下是工程代码：

#define WindowWidth 400 #define WindowHeight 400#define WindowTitle “OpenGL Mip纹理贴图&&同向异性过滤”#include <Windows.h>#include “GL/glew.h”#include <GL/freeglut.h>#include <stdio.h>#include <stdlib.h>//定义纹理对象编号 GLuint texGround;GLuint texWall;GLuint texSky;#define BMP_Header_Length 54 //图像数据在内存块中的偏移量 static GLfloat angle = 0.0f; //旋转角度 static GLfloat zPosition = 10;// 函数power_of_two用于判断一个整数是不是2的整数次幂 int power_of_two(int n){if (n <= 0)return 0;return (n & (n – 1)) == 0;}/* 函数load_texture 28.* 读取一个BMP文件作为纹理 29.* 如果失败，返回0，如果成功，返回纹理编号 30.*/GLuint load_texture(const char* file_name){GLint width, height, total_bytes;GLubyte* pixels = 0;GLuint last_texture_ID = 0, texture_ID = 0;// 打开文件，如果失败，返回 FILE* pFile = fopen(file_name, “rb”);if (pFile == 0)return 0;// 读取文件中图象的宽度和高度 fseek(pFile, 0x0012, SEEK_SET);fread(&width, 4, 1, pFile);fread(&height, 4, 1, pFile);fseek(pFile, BMP_Header_Length, SEEK_SET);// 计算每行像素所占字节数，并根据此数据计算总像素字节数 {GLint line_bytes = width * 3;while (line_bytes % 4 != 0)++line_bytes;total_bytes = line_bytes * height;}// 根据总像素字节数分配内存 pixels = (GLubyte*)malloc(total_bytes);if (pixels == 0){fclose(pFile);return 0;}// 读取像素数据 if (fread(pixels, total_bytes, 1, pFile) <= 0){free(pixels);fclose(pFile);return 0;}// 对就旧版本的兼容，如果图象的宽度和高度不是的整数次方，则需要进行缩放 // 若图像宽高超过了OpenGL规定的最大值，也缩放 {GLint max;glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max);if (!power_of_two(width)|| !power_of_two(height)|| width > max|| height > max){const GLint new_width = 256;const GLint new_height = 256; // 规定缩放后新的大小为边长的正方形 GLint new_line_bytes, new_total_bytes;GLubyte* new_pixels = 0;// 计算每行需要的字节数和总字节数 new_line_bytes = new_width * 3;while (new_line_bytes % 4 != 0)++new_line_bytes;new_total_bytes = new_line_bytes * new_height;// 分配内存 new_pixels = (GLubyte*)malloc(new_total_bytes);if (new_pixels == 0){free(pixels);fclose(pFile);return 0;}// 进行像素缩放 gluScaleImage(GL_RGB,width, height, GL_UNSIGNED_BYTE, pixels,new_width, new_height, GL_UNSIGNED_BYTE, new_pixels);// 释放原来的像素数据，把pixels指向新的像素数据，并重新设置width和height free(pixels);pixels = new_pixels;width = new_width;height = new_height;}}// 分配一个新的纹理编号 glGenTextures(1, &texture_ID);if (texture_ID == 0){free(pixels);fclose(pFile);return 0;}// 绑定新的纹理，载入纹理并设置纹理参数 // 在绑定前，先获得原来绑定的纹理编号，以便在最后进行恢复 GLint lastTextureID = last_texture_ID;glGetIntegerv(GL_TEXTURE_BINDING_2D, &lastTextureID);glBindTexture(GL_TEXTURE_2D, texture_ID);/*glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);130. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); */GLfloat max_TexAni; //查询允许的各向异性数量glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &max_TexAni);glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, max_TexAni);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);/* glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, 140. GL_BGR_EXT, GL_UNSIGNED_BYTE, pixels); */gluBuild2DMipmaps(GL_TEXTURE_2D, 3, width, height, GL_BGR_EXT, GL_UNSIGNED_BYTE, pixels);glBindTexture(GL_TEXTURE_2D, lastTextureID); //恢复之前的纹理绑定 free(pixels);return texture_ID;}void Display(void){// 清除屏幕 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// 设置视角 glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(65, 1, 1, 100);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0, 0, zPosition, 0, 0, 0, 0, 1, 0);glRotatef(angle, 0.0f, 1.0f, 0.0f); //旋转 // 绘制左侧墙壁以及纹理 glBindTexture(GL_TEXTURE_2D, texWall);glBegin(GL_QUADS);glTexCoord2f(0.0f, 0.0f); glVertex3f(-5.0f, -5.0f, 100.0f);glTexCoord2f(30.0f, 0.0f); glVertex3f(-5.0f, -5.0f, -100.0f);glTexCoord2f(30.0f, 2.0f); glVertex3f(-5.0f, 5.0f, -100.0f);glTexCoord2f(0.0f, 2.0f); glVertex3f(-5.0f, 5.0f, 100.0f);glEnd();//绘制右侧墙 glBegin(GL_QUADS);glTexCoord2f(0.0f, 0.0f); glVertex3f(5.0f, -5.0f, 100.0f);glTexCoord2f(30.0f, 0.0f); glVertex3f(5.0f, -5.0f, -100.0f);glTexCoord2f(30.0f, 2.0f); glVertex3f(5.0f, 5.0f, -100.0f);glTexCoord2f(0.0f, 2.0f); glVertex3f(5.0f, 5.0f, 100.0f);glEnd();//绘制地板 glBindTexture(GL_TEXTURE_2D, texGround);glBegin(GL_QUADS);glTexCoord2f(0.0f, 0.0f); glVertex3f(-5.0f, -5.0f, 100.0f);glTexCoord2f(0.0f, 1.0f); glVertex3f(5.0f, -5.0f, 100.0f);glTexCoord2f(25.0f, 1.0f); glVertex3f(5.0f, -5.0f, -100.0f);glTexCoord2f(25.0f, 0.0f); glVertex3f(-5.0f, -5.0f, -100.0f);glEnd();//绘制顶层 glBindTexture(GL_TEXTURE_2D, texSky);glBegin(GL_QUADS);glTexCoord2f(0.0f, 0.0f); glVertex3f(-5.0f, 5.0f, 100.0f);glTexCoord2f(0.0f, 3.0f); glVertex3f(5.0f, 5.0f, 100.0f);glTexCoord2f(35.0f, 3.0f); glVertex3f(5.0f, 5.0f, -100.0f);glTexCoord2f(35.0f, 0.0f); glVertex3f(-5.0f, 5.0f, -100.0f);glEnd();glutSwapBuffers();}void SpecialKey(GLint key, GLint x, GLint y){if (key == GLUT_KEY_UP){zPosition += 1.0f;}if (key == GLUT_KEY_DOWN){zPosition -= 1.0f;}if (key == GLUT_KEY_LEFT){angle += 0.5f;}if (key == GLUT_KEY_RIGHT){angle -= 0.5f;}glutPostRedisplay();}int main(int argc, char* argv[]){// GLUT初始化 glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);glutInitWindowPosition(100, 100);glutInitWindowSize(WindowWidth, WindowHeight);glutCreateWindow(WindowTitle);glEnable(GL_DEPTH_TEST);glEnable(GL_TEXTURE_2D); // 启用纹理 texGround = load_texture(“ground.bmp”); //加载纹理 texWall = load_texture(“wall.bmp”);texSky = load_texture(“sky.bmp”);glutDisplayFunc(&Display); //回调函数 glutSpecialFunc(&SpecialKey);glutMainLoop(); //循环调用 return 0;}