隧道示例程序使用了和纹理有关的内容，并在视觉上显示了不同的过滤器和贴图模式。
该示例程序在启动时加载3个纹理用于对一个隧道进行渲染。
声明变量与定义宏
首先为3个纹理对象创建标识符。textures数组将包含3个整数，通过宏TEXTURE_BRICK、TEXTURE_FLOOR 、 TEXTURE_CEILING访问，以及数量宏TEXTURE_COUNT，并且创建一个名称数组szTextureFiles。
// 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
GLuint textures[TEXTURE_COUNT];
const char *szTextureFiles[TEXTURE_COUNT] = { "brick.tga", "floor.tga", "ceiling.tga" };
初始化纹理对象
纹理对象是在SetupRC函数中配置的
glGenTextures(TEXTURE_COUNT,textures);
然后是一个简单循环，依次绑定每一个纹理对象，并设置纹理对象的参数。
GLbyte *pBytes;
GLint iWidth,iHeight,iComponents;
GLenum eFormat;
GLint iLoop;
for (iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++) {
glBindTexture(GL_TEXTURE_2D, textures[iLoop]);
pBytes = gltReadTGABits(szTextureFiles[iLoop], &iWidth, &iHeight, &iComponents, &eFormat);
//纹理参数-邻近过滤
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
//环绕方式
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S , GL_CLAMP_TO_EDGE);
glTexParameterf(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);
//生成Mip贴图
glGenerateMipmap(GL_TEXTURE_2D);
//释放
free(pBytes);
}
设置顶点数据
隧道地板顶点设置
GLfloat z;
//隧道顶点设置
floorBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
//Z表示深度，隧道的深度
for(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();
隧道上方顶点设置
ceilingBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
for(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();
隧道左右墙体顶点设置
leftWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
for(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(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();
渲染纹理
渲染是在RenderScene函数中完成的。
清空颜色、模型视图矩阵Z轴平移、着色器
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
modelViewMatrix.PushMatrix();
modelViewMatrix.Translate(0, 0, viewZ);
shaderManager.UseStockShader(GLT_SHADER_TEXTURE_REPLACE,transformPipeline.GetModelViewProjectionMatrix(),0);
绑定对应纹理对象进行批次类绘制
glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_FLOOR]);
floorBatch.Draw();
glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_CEILING]);
ceilingBatch.Draw();
glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_BRICK]);
leftWallBatch.Draw();
rightWallBatch.Draw();
出栈、交互缓存区
modelViewMatrix.PopMatrix();
glutSwapBuffers();
键盘控制移动
通过修改平移z轴坐标控制前进、后退。
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();
}
切换过滤器
创建过滤器切换菜单
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);
切换过滤器处理
void ProcessMenu(int value)
{
GLint iLoop;
for(iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++)
{
/**绑定纹理 glBindTexture
参数1：GL_TEXTURE_2D
参数2：需要绑定的纹理对象
*/
glBindTexture(GL_TEXTURE_2D, textures[iLoop]);
/**配置纹理参数 glTexParameteri
参数1：纹理模式
参数2：纹理参数
参数3：特定纹理参数
*/
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();
}
删除纹理标识符
//关闭渲染环境
void ShutdownRC(void)
{
//删除纹理
glDeleteTextures(TEXTURE_COUNT, textures);
}
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