OpenGL: 纹理

1. 原始图像数据

像素包装
图像存储空间 = 图像width * 图像height * 每个像素的字节数
在OpenGL中：使用4字节的行对齐方式，每一行补全到4的倍数，使用glPixelStorei(pname,param)可以改变或者恢复像素的存储方式

2. 从颜色缓存区内容作为像素图直接读取
void glReadPixels(GLint x,GLint y,GLSizei width,GLSizei
height, GLenum format, GLenum type,const void * pixels);

3. 像素图数据的获取过程（从硬盘到内存）
gltReadTGABits(szFileName,iWidth,iHeight,iComponents,eFormat)

4.纹理载入方式（图像数据从内存到纹理缓冲区）：
`glTexImage1D/glTexImage2D/glTexImage3D
glTexImage2D(target,level,internalformat,width,height,border,format,type,*data)

5.纹理对象

//使用函数分配纹理对象
//指定纹理对象的数量和指针(指针指向一个无符号整形数组，由纹理对象标识符填充)。 void glGenTextures(GLsizei n,GLuint * textTures);

//绑定纹理状态
void glBindTexture(GLenum target,GLunit texture);

//删除绑定纹理对象
void glDeleteTextures(GLsizei n,GLuint *textures);

//测试纹理对象是否有效 //如果texture是个已经分配空间的纹理对象，那么这个函数会返回GL_TRUE,否则会返回GL_FALSE。 GLboolean glIsTexture(GLuint texture);

`5.1 设置纹参数
glTexParameterf(GLenum target,GLenum pname,GLFloat param);
glTexParameteri(GLenum target,GLenum pname,GLint param);
glTexParameterfv(GLenum target,GLenum pname,GLFloat *param);
glTexParameteriv(GLenum target,GLenum pname,GLint *param);

5.2 设置过滤式
邻近过滤(GL_NEAREST) 线性过滤(GL_LINEAR)
。
2种纹理过滤方式比较

glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST) 纹理缩小时,使用邻近过滤
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST) 纹理放大时,使用线性过滤
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_HEAREST
);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_HEAREST
);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR)
;
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR)
;

5.3 设置环绕方式
参数1:GL_TEXTURE_1D、 GL_TEXTURE_2D、GL_TEXTURE_3D 参数2:GL_TEXTURE_WRAP_S、GL_TEXTURE_T、GL_TEXTURE_R,针对s,t,r坐标参数3:GL_REPEAT、GL_CLAMP、GL_CLAMP_TO_EDGE、GL_CLAMP_TO_BORDER
GL_REPEAT:OpenGL 在纹理坐标超过1.0的方向上对纹理进行重复; GL_CLAMP:所需的纹理单元取自纹理边界或TEXTURE_BORDER_COLOR. GL_CLAMP_TO_EDGE环绕模式强制对范围之外的纹理坐标沿着合法的纹理单元的最后或者最后
来进采样。 GL_CLAMP_TO_BORDER:在纹坐标在0.0到1.0范围之外的只使边界纹单元。边界纹理单元是
作为围绕基本图像的额外的和，并与基本纹图像起加载的。
glTextParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAR_S,GL_CLAMP_TO_EDGE);
glTextParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAR_T,GL_CLAMP_TO_EDGE);

示例：金字塔

void SetupRC()
{
    
    glClearColor(0.7f, 0.7f,0.7f, 1.0f);
    
    shaderManager.InitializeStockShaders();
    
    glEnable(GL_DEPTH_TEST);
    
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_2D, textureID);
    
    LoadTGATexture("stone.tga", GL_LINEAR, GL_LINEAR, GL_CLAMP_TO_EDGE);
    MakePyramid(pyramidBatch);
    
    cameraFrame.MoveForward(-10.0);
    
}

// 将TGA文件加载为2D纹理

bool LoadTGATexture(const char *szFileName, GLenum minFilter, GLenum magFilter, GLenum wrapMode)
{
    GLbyte *pBits;
    int nWidth,nHeight,nComponents;
    GLenum eFormat;
    
    //1.读取纹理的像素
    pBits =  gltReadTGABits(szFileName, &nWidth, &nHeight, &nComponents, &eFormat);
    
    if (pBits == NULL) {
        
        printf("读取纹理像素失败\n");
        return  false;
    }
    
    //2.设置纹理参数
    //设置s,t的环绕方式
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrapMode);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrapMode);
    
    //设置放大\缩小的过滤方式
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, minFilter);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, magFilter);
    
    
    //3.精密包装像素数据
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    
    //4.载入纹理
    glTexImage2D(GL_TEXTURE_2D, 0, nComponents, nWidth, nHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBits);
    
    
    //使用完释放
    free(pBits);
    
    if(minFilter == GL_LINEAR_MIPMAP_LINEAR ||
       minFilter == GL_LINEAR_MIPMAP_NEAREST ||
       minFilter == GL_NEAREST_MIPMAP_LINEAR ||
       minFilter == GL_NEAREST_MIPMAP_NEAREST)
        glGenerateMipmap(GL_TEXTURE_2D);

    
    return true;
}

//绘制金字塔

//绘制金字塔
void MakePyramid(GLBatch&  pyramidBatch)
{

    //1.pyramidBatch
    pyramidBatch.Begin(GL_TRIANGLES, 18,1);
    
    
    //----------vBlackLeft------------
    //设置法线坐标-光照
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);

    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    
    //设置顶点坐标
    pyramidBatch.Vertex3f(-1.0f, -1.0f, -1.0f);
    
    //------vBlackRight------------
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
    pyramidBatch.Vertex3f(1.0f, -1.0f, -1.0f);
   
    //vFrontRight点
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
    pyramidBatch.Vertex3f(1.0f, -1.0f, 1.0f);
    
    
    //三角形Y
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
    pyramidBatch.Vertex3f(-1.0f, -1.0f, 1.0f);
    
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    pyramidBatch.Vertex3f(-1.0f, -1.0f, -1.0f);
    
    pyramidBatch.Normal3f(0.0f, -1.0f, 0.0f);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
    pyramidBatch.Vertex3f(1.0f, -1.0f, 1.0f);

    //塔顶
    M3DVector3f vApex = {0.0f,1.0f,0.0f};
    M3DVector3f vFrontLeft = {-1.0f,-1.0f,1.0f};
    M3DVector3f vFrontRight = {1.0f,-1.0f,1.0f};
    M3DVector3f vBackLeft = {-1.0f,-1.0f,-1.0f};
    M3DVector3f vBackRight = {1.0f,-1.0f,-1.0f};
    
    //目的:为了临时存储法线向量
    M3DVector3f n;
    
    //金字塔的前面
    //三角形:(Apex,vFrontLeft,vFrontRight)
    
    m3dFindNormal(n, vApex, vFrontLeft, vFrontRight);
    
    //vApex
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.5, 1.0f);
    pyramidBatch.Vertex3fv(vApex);
    
    //vFrontLeft
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    pyramidBatch.Vertex3fv(vFrontLeft);
    
    //vFrongRight
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
    pyramidBatch.Vertex3fv(vFrontRight);

    
    //金字塔的左边
    //三角形:(Apex,vBackLeft,vFrontLeft)
    m3dFindNormal(n, vApex, vBackLeft, vFrontLeft);

    //vApex
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.5f, 1.0f);
    pyramidBatch.Vertex3fv(vApex);
    
    //vBackLeft
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
    pyramidBatch.Vertex3fv(vBackLeft);
    
    //vFrontLeft
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    pyramidBatch.Vertex3fv(vFrontLeft);
    
    //金字塔右边
    //三角形：（vApex, vFrontRight, vBackRight）
    m3dFindNormal(n, vApex, vFrontRight, vBackRight);
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.5f, 1.0f);
    pyramidBatch.Vertex3fv(vApex);
    
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
    pyramidBatch.Vertex3fv(vFrontRight);
    
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    pyramidBatch.Vertex3fv(vBackRight);
    
    //金字塔后边
    //三角形：（vApex, vBackRight, vBackLeft）
    m3dFindNormal(n, vApex, vBackRight, vBackLeft);
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.5f, 1.0f);
    pyramidBatch.Vertex3fv(vApex);
    
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
    pyramidBatch.Vertex3fv(vBackRight);
    
    pyramidBatch.Normal3fv(n);
    pyramidBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
    pyramidBatch.Vertex3fv(vBackLeft);
    
    //结束批次设置
    pyramidBatch.End(); 
}

代码稍后上传：

OpenGL：纹理

OpenGL: 纹理

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