一、MIP贴图

Mip贴图：是纹理的一种渲染技巧。用来提高渲染的性能、提高显示的质量。

应用场景：在图像很大或者很小的时候，这时候进行移动改变深度值的时候；或者有一个大图要进行等份、等比例缩小的时候，就需要考虑使用Mip贴图来避免闪烁情况

API:

//设置mip贴图基层 0是最底层
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_BASE_LEVEL,0);
//为纹理对象生成一组完整的mip贴图
//参数1：纹理维度，GL_TEXTURE_1D,GL_TEXTURE_2D,GL_TEXTURE_3D
glGenerateMipmap(GL_TEXTURE_2D);

二、案例

1、效果图

2、分析

• 一定要注意，搞清楚各个顶点对应的 顶点坐标和纹理坐标

3、流程图

4、源码

#include "GLTools.h"
#include "GLShaderManager.h"
#include "GLFrustum.h"
#include "GLBatch.h"
#include "GLFrame.h"
#include "GLMatrixStack.h"
#include "GLGeometryTransform.h"

#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif



GLShaderManager         shaderManager;            //着色器管理器
GLMatrixStack           modelViewMatrix;        //模型视图矩阵
GLMatrixStack           projectionMatrix;        //投影矩阵
GLFrustum               viewFrustum;            //视景体
GLGeometryTransform      transformPipeline;        //几何变换管线

//4个批次容器类
GLBatch             floorBatch;//地面
GLBatch             ceilingBatch;//天花板
GLBatch             leftWallBatch;//左墙面
GLBatch             rightWallBatch;//右墙面

//设置一个深度初始值，-65。
GLfloat             viewZ = -65.0f;


// 纹理标识符号
#define TEXTURE_BRICK   0 //墙面
#define TEXTURE_FLOOR   1 //地板
#define TEXTURE_CEILING 2 //纹理天花板
#define TEXTURE_COUNT   3 //纹理个数


//纹理标记数组
GLuint  textures[TEXTURE_COUNT];
//文件tag名字数组
const char *szTextureFiles[TEXTURE_COUNT] = { "brick.tga", "floor.tga", "ceiling.tga" };



void ChangeSize(int w, int h)
{
    if (h == 0) {
        h = 1;
    }
    
    glViewport(0, 0, w, h);
    
    viewFrustum.SetPerspective(35.0f, float(w)/float(h), 1.0f, 120.0f);
    
    projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
    
    transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}



//在这个函数里能够在渲染环境中进行任何需要的初始化，它这里的设置并初始化纹理对象
void SetupRC()
{
    //1、背景色
    glClearColor(0, 0, 0, 1);
    //2、初始化着色器
    shaderManager.InitializeStockShaders();
    
    
    //3、加载纹理部分
    //1、分配纹理
    glGenTextures(TEXTURE_COUNT, textures);
    
    //2、初始化我们需要用的参数
    //指针
    GLbyte *pBytes;
    //宽、高、组件
    GLint iWidth,iHeight,iComponents;
    //格式
    GLenum eFormat;
    //定义一个i
    GLint iLoop;
    
    //3、我们这次要进行4个面的纹理处理，为了方便，这里循环绑定纹理
    //我们需要设置纹理的参数，就需要先确认是对哪个纹理进行设置，这时候就靠绑定纹理来搞定了
    //就是我们先绑定纹理A，然后对A进行设置。之后是B、C...
    //和RenderScene中一样。要先确认是哪个纹理，才开始draw
    for (iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++) {
        //绑定纹理
        glBindTexture(GL_TEXTURE_2D, textures[iLoop]);
        //拿到相关的参数
        pBytes = gltReadTGABits(szTextureFiles[iLoop], &iWidth, &iHeight, &iComponents, &eFormat);
        //设置参数
        //过滤方式
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        //环绕方式
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        
        //载入纹理
        glTexImage2D(GL_TEXTURE_2D, 0, iComponents, iWidth, iHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBytes);
        //为纹理对象生成完整的mip贴图
        glGenerateMipmap(GL_TEXTURE_2D);
        
        //用完释放
        free(pBytes);
    }
    
    
    
    //初始化4个墙面的顶点数据和纹理坐标
    //利用三角形带的图元连接方式
    //连接方式，28个顶点，1个纹理
    floorBatch.Begin(GL_TRIANGLE_STRIP, 28,1);
    for(GLfloat z = 60.0f; z >= 0.0f; z -=10.0f)
    {
        floorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
        floorBatch.Vertex3f(-10.0f, -10.0f, z);
        
        floorBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
        floorBatch.Vertex3f(10.0f, -10.0f, z);
        
        floorBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
        floorBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);
        
        floorBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
        floorBatch.Vertex3f(10.0f, -10.0f, z - 10.0f);
    }
    floorBatch.End();
    
    
    ceilingBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
    for(GLfloat z = 60.0f; z >= 0.0f; z -=10.0f)
    {
        ceilingBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
        ceilingBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);
        
        ceilingBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
        ceilingBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);
        
        ceilingBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
        ceilingBatch.Vertex3f(-10.0f, 10.0f, z);
        
        ceilingBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
        ceilingBatch.Vertex3f(10.0f, 10.0f, z);
    }
    ceilingBatch.End();
    
    
    
    leftWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
    for(GLfloat z = 60.0f; z >= 0.0f; z -=10.0f)
    {
        leftWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
        leftWallBatch.Vertex3f(-10.0f, -10.0f, z);
        
        leftWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
        leftWallBatch.Vertex3f(-10.0f, 10.0f, z);
        
        leftWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
        leftWallBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);
        
        leftWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
        leftWallBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);
    }
    leftWallBatch.End();
    
    
    rightWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
    for(GLfloat z = 60.0f; z >= 0.0f; z -=10.0f)
    {
        rightWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
        rightWallBatch.Vertex3f(10.0f, -10.0f, z);
        
        rightWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
        rightWallBatch.Vertex3f(10.0f, 10.0f, z);
        
        rightWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
        rightWallBatch.Vertex3f(10.0f, -10.0f, z - 10.0f);
        
        rightWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
        rightWallBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);
    }
    rightWallBatch.End();
    
    
}

//关闭渲染环境
void ShutdownRC(void)
{
    //删除所用到的3个纹理
    glDeleteTextures(3, textures);
}

//调用，绘制场景
void RenderScene(void)
{
    //1
    glClear(GL_COLOR_BUFFER_BIT);
    
    //2、压栈
    modelViewMatrix.PushMatrix();
    //矩阵直接记录移动
    modelViewMatrix.Translate(0, 0, viewZ);
    
    //3、纹理替换矩阵着色器
    shaderManager.UseStockShader(GLT_SHADER_TEXTURE_REPLACE,transformPipeline.GetModelViewProjectionMatrix(),0);
    //4、绘制。
    //因为我们有4个面需要绘制。为了以防万一，绑定了错误的纹理，这里重新绑定一次
    glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_FLOOR]);
    floorBatch.Draw();
    
    glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_CEILING]);
    ceilingBatch.Draw();
    
    //左右使用的是一样的纹理图案。这里绑定一次就行了
    glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_BRICK]);
    leftWallBatch.Draw();
    rightWallBatch.Draw();
    
    //出栈
    modelViewMatrix.PopMatrix();
    
    //交换缓冲区
    glutSwapBuffers();
}

void SpecialKeys(int key, int x, int y)
{
    if (key == GLUT_KEY_UP) {
        viewZ += 0.5f;
    }
    
    if (key == GLUT_KEY_DOWN) {
        viewZ -= 0.5f;
    }
    
    glutPostRedisplay();
}

void ProcessMenu(int value)
{
    //这里用循环，还是因为一旦改变，4个面都需要做改变
    for (GLint iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++) {
        
        //还是要先确定 改变的是哪个纹理的属性。所以先绑定
        glBindTexture(GL_TEXTURE_2D, textures[iLoop]);
        
        switch(value)
        {
            case 0:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_NEAREST（最邻近过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
                break;
                
            case 1:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_LINEAR（线性过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                break;
                
            case 2:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_NEAREST_MIPMAP_NEAREST（选择最邻近的Mip层，并执行最邻近过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
                break;
                
            case 3:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_NEAREST_MIPMAP_LINEAR（在Mip层之间执行线性插补，并执行最邻近过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
                break;
                
            case 4:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_NEAREST_MIPMAP_LINEAR（选择最邻近Mip层，并执行线性过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
                break;
                
            case 5:
                //GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER(缩小过滤器)，GL_LINEAR_MIPMAP_LINEAR（在Mip层之间执行线性插补，并执行线性过滤，又称为三线性过滤）
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
                break;
                
            case 6:
            
                //设置各向异性过滤
                GLfloat fLargest;
                //获取各向异性过滤的最大数量
                glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &fLargest);
                //设置纹理参数(各向异性采样)
                glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, fLargest);
                break;
        
            case 7:
                //设置各向同性过滤，数量为1.0表示(各向同性采样)
                glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 1.0f);
                break;
                
        }
    }
    
    //触发重画
    glutPostRedisplay();
}

int main (int argc ,char *argv[]){
    
    //一如既往的准备工作
    //设置工作目录
    gltSetWorkingDirectory(argv[0]);
    //初始化glut库
    glutInit(&argc, argv);
    //初始化双缓冲区窗口
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    //设置大小
    glutInitWindowSize(800, 800);
    //设置名称
    glutCreateWindow("隧道-Mip贴图");
    //初始化GLEW库
    GLenum status = glewInit();
    if (GLEW_OK != status) {
        printf("GLEW Error:%s\n",glewGetErrorString(status));
        return 1;
    }
    
    //1
    glutReshapeFunc(ChangeSize);
    //2
    glutDisplayFunc(RenderScene);
    //3
    glutSpecialFunc(SpecialKeys);
    //4
    glutCreateMenu(ProcessMenu);
    glutAddMenuEntry("GL_NEAREST", 0);
    glutAddMenuEntry("GL_LINEAR", 1);
    glutAddMenuEntry("GL_NEAREST_MIPMAP_NEAREST", 2);
    glutAddMenuEntry("GL_NEAREST_MIPMAP_LINEAR", 3);
    glutAddMenuEntry("GL_LINEAR_MIPMAP_NEAREST", 4);
    glutAddMenuEntry("GL_LINEAR_MIPMAP_LINEAR", 5);
    glutAddMenuEntry("Anisotropic Filter", 6);
    glutAddMenuEntry("Anisotropic Off", 7);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
    //5
    SetupRC();
    glutMainLoop();
    //6
    ShutdownRC();
    
    return 0;
}

5、注意事项

• 注意创建好纹理对象之后，要分别绑定、然后进行设置
• 在RenderScene方法中，在draw之前，为了防止弄不清楚当前的纹理对象，要重新绑定一次