osg-geometry shader-贝塞尔曲线

#include <osg/Program>
#include <osg/LineWidth>
#include <osgDB/ReadFile>
#include <osgViewer/Viewer>

static const char* vertSource = {
"#version 120\n"
"#extension GL_EXT_geometry_shader4 : enable\n"
"void main()\n"
"{ gl_Position = ftransform(); }\n"
};

static const char* geomSource = {
"#version 120\n"
"#extension GL_EXT_geometry_shader4 : enable\n"
"uniform int segments;\n"
"void main(void)\n"
"{\n"
" float delta = 1.0 / float(segments);\n"
" vec4 v;\n"
" for ( int i=0; i<=segments; ++i )\n"
" {\n"
" float t = delta * float(i);\n"
" float t2 = t * t;\n"
" float one_minus_t = 1.0 - t;\n"
" float one_minus_t2 = one_minus_t * one_minus_t;\n"
" v = gl_PositionIn[0] * one_minus_t2 * one_minus_t+ \n"
" gl_PositionIn[1] * 3.0 * t * one_minus_t2 +\n"
" gl_PositionIn[2] * 3.0 * t2 * one_minus_t +\n"
" gl_PositionIn[3] * t2 * t;\n"
" gl_Position = v;\n"
" EmitVertex();\n"
" }\n"
" EndPrimitive();\n"
"}\n"
};

int main(int argc, char** argv)
{
osg::ref_ptr<osg::Vec3Array> vertices = new osg::Vec3Array;
vertices->push_back(osg::Vec3(0.0f, 0.0f, 0.0f));
vertices->push_back(osg::Vec3(1.0f, 1.0f, 1.0f));
vertices->push_back(osg::Vec3(2.0f, 1.0f, -1.0f));
vertices->push_back(osg::Vec3(3.0f, 0.0f, 0.0f));
osg::ref_ptr<osg::Geometry> controlPoints = new osg::Geometry;
controlPoints->setVertexArray(vertices.get());
controlPoints->addPrimitiveSet(
new osg::DrawArrays(GL_LINES_ADJACENCY_EXT, 0, 4));

osg::ref_ptr<osg::Geode> geode = new osg::Geode;
geode->addDrawable(controlPoints.get());

int segments = 10;
osg::ref_ptr<osg::Program> program = new osg::Program;
program->addShader(
new osg::Shader(osg::Shader::VERTEX, vertSource));
program->addShader(
new osg::Shader(osg::Shader::GEOMETRY, geomSource));
program->setParameter(GL_GEOMETRY_VERTICES_OUT_EXT, segments + 1);
program->setParameter(GL_GEOMETRY_INPUT_TYPE_EXT,
GL_LINES_ADJACENCY_EXT);
program->setParameter(GL_GEOMETRY_OUTPUT_TYPE_EXT,
GL_LINE_STRIP);

osg::ref_ptr<osg::LineWidth> lineWidth = new osg::LineWidth;
lineWidth->setWidth(2.0f);

osg::StateSet* stateset = geode->getOrCreateStateSet();
stateset->setAttributeAndModes(program.get());
stateset->setAttribute(lineWidth.get());
stateset->setMode(GL_LIGHTING, osg::StateAttribute::ON);
stateset->addUniform(new osg::Uniform("segments", segments));

 

osgViewer::Viewer viewer;

viewer.setSceneData(geode.get());
return viewer.run();

}