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：
