osgtexture1D这一课主要讲解了osg中一维纹理的使用,一维纹理在计算机图形学中用的远没有二维纹理那么广泛,我们看看示例中的实现。
一维纹理可以看做是二维纹理的一种特殊情况,它的图片高度只有一个像素,在示例中一维纹理的图片是采用程序生成的
//给模型创建一个一维纹理的渲染状态
osg::StateSet* create1DTextureStateToDecorate(osg::Node* loadedModel)
{
//使用程序生成图片
osg::Image* image = new osg::Image;
int noPixels = 1024;
image->allocateImage(noPixels,1,1,GL_RGBA,GL_FLOAT);
image->setInternalTextureFormat(GL_RGBA);
typedef std::vector ColorBands;
ColorBands colorbands;
colorbands.push_back(osg::Vec4(0.0f,0.0,0.0,1.0f));
colorbands.push_back(osg::Vec4(1.0f,0.0,0.0,1.0f));
colorbands.push_back(osg::Vec4(1.0f,1.0,0.0,1.0f));
colorbands.push_back(osg::Vec4(0.0f,1.0,0.0,1.0f));
colorbands.push_back(osg::Vec4(0.0f,1.0,1.0,1.0f));
colorbands.push_back(osg::Vec4(0.0f,0.0,1.0,1.0f));
colorbands.push_back(osg::Vec4(1.0f,0.0,1.0,1.0f));
colorbands.push_back(osg::Vec4(1.0f,1.0,1.0,1.0f));
float nobands = colorbands.size();
float delta = nobands/(float)noPixels;
float pos = 0.0f;
osg::Vec4* dataPtr = (osg::Vec4*)image->data();
//从0-127像素全是黑色(0.0f,0.0,0.0,1.0f)
//从128-255像素全是红色(1.0f,0.0,0.0,1.0f)
//...依次直到第1023像素全是白色(1.0f,1.0,1.0,1.0f)
for(int i=0;isetWrap(osg::Texture1D::WRAP_S,osg::Texture1D::MIRROR);
texture->setFilter(osg::Texture1D::MIN_FILTER,osg::Texture1D::LINEAR);
texture->setImage(image);
//覆盖(Override)子节点的渲染状态
osg::Material* material = new osg::Material;
osg::StateSet* stateset = new osg::StateSet;
stateset->setTextureAttribute(0,texture,osg::StateAttribute::OVERRIDE);
stateset->setTextureMode(0,GL_TEXTURE_1D,osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
stateset->setTextureMode(0,GL_TEXTURE_2D,osg::StateAttribute::OFF|osg::StateAttribute::OVERRIDE);
stateset->setTextureMode(0,GL_TEXTURE_3D,osg::StateAttribute::OFF|osg::StateAttribute::OVERRIDE);
stateset->setTextureMode(0,GL_TEXTURE_GEN_S,osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
stateset->setAttribute(material,osg::StateAttribute::OVERRIDE);
return stateset;
}
void animateTexGen(osg::TexGenNode* texgenNode,double time)
{
const double timeInterval = 2.0f; //更新间隔时间
static double previousTime = time;
static bool state = false;
while (time>previousTime+timeInterval)
{
previousTime+=timeInterval;
state = !state;
}
if (state)
{
//物体空间模式
texgenNode->getTexGen()->setMode(osg::TexGen::OBJECT_LINEAR);
}
else
{
//相机空间模式(根据物体到相机的远近会修改纹理坐标)
texgenNode->getTexGen()->setMode(osg::TexGen::EYE_LINEAR);
}
}
之后我们设置纹理坐标节点osg::TexGenNode,并设置它计算的平面参数,并把它添加到场景中:
osg::TexGenNode* texgenNode = new osg::TexGenNode;
texgenNode->setReferenceFrame( osg::TexGenNode::ABSOLUTE_RF );
texgenNode->getTexGen()->setMode( osg::TexGen::OBJECT_LINEAR );
const osg::BoundingSphere& bs = loadedModel->getBound();
float zBase = bs.center().z()-bs.radius();
float zScale = 2.0f/bs.radius();
texgenNode->getTexGen()->setPlane(osg::TexGen::S,osg::Plane(0.0f,0.0f,zScale,-zBase));
texgenNode->setUpdateCallback(new AnimateTexGenCallback());
root -> addChild( texgenNode );
看到这里一般会有两个疑问:1、为什么一个普通的StateAttribute还需要有一个节点呢?我们接触的一般osg::PolygonMode等等也不会需要一个osg::PolygonModeNode这样的节点类配合它起作用啊? 2、为什么不是将模型loadedModel添加到texgenNode下面作为它的子节点呢?
对于第一个疑问:因为在TexGen中如果设置模式是osg::TexGen::EYE_LINEAR,需要知道TexGen这时候的模型视图矩阵用来计算物体在眼坐标下到指定平面的距离(参考OpenGL之自动纹理生成),第二个疑问可以查看osg论坛中Robert对此的解释:osgtexture1d example / osg::TexGenNode order,不需要添加为子节点,因为OSG中只会记录一个TexGenNode的位置,并把它作为OpenGL的一个状态来使用。