基础图元简单矢量_图元低码-优快云博客

这篇博客介绍了如何使用osg库在OpenSceneGraph中创建并渲染一个带有透明效果的3D正方形。首先，申请顶点数组定义四边形的四个顶点，然后设置颜色数组为半透明颜色，接着指定法向量。接着，创建几何对象Geometry，并设置顶点、颜色和法向量数组。最后，在Geode中添加这个几何对象，并开启透明模式和设置线宽，以呈现线条轮廓。

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创建简单矢量图

基础：

OSG坐标系，与笛卡尔三维坐标系方向相同

步骤：

申请顶点数组，设置垂直xoy面的正方形的四个顶点

osg::ref_ptr<osg::Vec3Array> coords = new osg::Vec3Array;

coords->push_back(osg::Vec3(-10.0, 5.0, -10.0));
coords->push_back(osg::Vec3(10.0, 5.0, -10.0));
coords->push_back(osg::Vec3(10.0, 5.0, 10.0));
coords->push_back(osg::Vec3(-10.0, 5.0, 10.0));

申请颜色数组，设置半透明的颜色组

osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;

colors->push_back(osg::Vec4f(1.0, 0.0, 0.0, 0.5));
colors->push_back(osg::Vec4f(0.0, 1.0, 0.0, 0.5));
colors->push_back(osg::Vec4f(0.0, 0.0, 1.0, 0.5));
colors->push_back(osg::Vec4f(1.0, 1.0, 0.0, 0.5));

申请法向量，令光源在正方形的一侧，压入一个法向量

osg::ref_ptr<osg::Vec3Array> norms = new osg::Vec3Array;

norms->push_back(osg::Vec3(0.0, -1.0, 0.0));

申请一个几何Geometry

osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;

设置顶点和顶点的关联方式

geom->setVertexArray(coords.get());
geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::Mode::QUADS, 0, 4));

设置顶点颜色

geom->setColorArray(colors.get());
geom->setColorBinding(osg::Geometry::AttributeBinding::BIND_PER_VERTEX);

设置法向量

geom->setNormalArray(norms.get());
geom->setNormalBinding(osg::Geometry::AttributeBinding::BIND_OVERALL);

申请一个Geode

osg::ref_ptr<osg::Geode> geode = new osg::Geode;

在Geode中绘制几何，打开透明

geode->addDrawable(geom.get());
geode->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);

将上一节中main函数中的CreateBox()改为CreateSimple()，运行

申请一个限制线宽

osg::ref_ptr<osg::LineWidth> width = new osg::LineWidth;

将顶点关联方式改为LINE_LOOP

geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::Mode::LINE_LOOP, 0, 4));

设置线宽
```
width->setWidth(5.0);
```
运行，查看结果

完整代码

#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgGA/GUIEventAdapter>
#include <osgViewer/ViewerEventHandlers>
#include <osg/Geode>
#include <osg/ShapeDrawable>
#include <osg/Material>
#include <osg/StateSet>
#include <osg/Image>
#include <osg/Texture2D>
#include <osg/LineWidth>
#include <iostream>
using namespace std;

osg::ref_ptr<osg::Geode> CreateSimple() {
	osg::ref_ptr<osg::Geode> geode = new osg::Geode;
	osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;
	osg::ref_ptr<osg::Vec3Array> coords = new osg::Vec3Array;
	osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;
	osg::ref_ptr<osg::Vec3Array> norms = new osg::Vec3Array;
	osg::ref_ptr<osg::LineWidth> width = new osg::LineWidth;
	
    geode->addDrawable(geom.get());
	geode->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);
	geom->setVertexArray(coords.get());
	geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::Mode::LINE_LOOP, 0, 4));
	geom->setColorArray(colors.get());
	geom->setColorBinding(osg::Geometry::AttributeBinding::BIND_PER_VERTEX);
	geom->setNormalArray(norms.get());
	geom->setNormalBinding(osg::Geometry::AttributeBinding::BIND_OVERALL);
	width->setWidth(5.0);
	geode->getOrCreateStateSet()->setAttributeAndModes(width.get(), osg::StateAttribute::ON);

	coords->push_back(osg::Vec3(-10.0, 5.0, -10.0));
	coords->push_back(osg::Vec3(10.0, 5.0, -10.0));
	coords->push_back(osg::Vec3(10.0, 5.0, 10.0));
	coords->push_back(osg::Vec3(-10.0, 5.0, 10.0));

	colors->push_back(osg::Vec4f(1.0, 0.0, 0.0, 0.5));
	colors->push_back(osg::Vec4f(0.0, 1.0, 0.0, 0.5));
	colors->push_back(osg::Vec4f(0.0, 0.0, 1.0, 0.5));
	colors->push_back(osg::Vec4f(1.0, 1.0, 0.0, 0.5));

	norms->push_back(osg::Vec3(0.0, -1.0, 0.0));

	return geode;
}

int main() {

	osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer;
	osg::ref_ptr<osg::Group> group = new osg::Group;
	
	group->addChild(CreateSimple());
	viewer->setSceneData(group.get());

	return viewer->run();
}