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);
image.png
二、案例
1、效果图
061.gif
2、案例分析
-
一定要注意，搞清楚各个顶点对应的 顶点坐标和纹理坐标
image.png
3、流程图
image.png
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
