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Added clarifying comments in examples/osggeometry

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This commit is contained in:
Chris White
2017-04-24 15:55:40 -04:00
parent 6df273a865
commit 1f05290982
1 changed files with 32 additions and 18 deletions
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50
examples/osggeometry/osggeometry.cpp
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@@ -80,6 +80,9 @@ void printTriangles(const std::string& name, osg::Drawable& drawable)
}
/// Create a scene with examples of the different types of OpenGL primitives.
/// The primitives are the same as shown in the OpenGL diagram loaded in
/// createBackground() (Images/primitives.gif).
osg::Node* createScene()
{
// create the Geode (Geometry Node) to contain all our osg::Geometry objects.
@@ -124,7 +127,11 @@ osg::Node* createScene()
pointsGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
// set the normal in the same way color.
// Set the normal in the same way as the color.
// (0,-1,0) points toward the viewer, in the default coordinate
// setup. Even for POINTS, the normal specified here
// is used to determine how the geometry appears under different
// lighting conditions.
osg::Vec3Array* normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
pointsGeom->setNormalArray(normals, osg::Array::BIND_OVERALL);
@@ -170,7 +177,9 @@ osg::Node* createScene()
linesGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
// set the normal in the same way color.
// Set the normal in the same way as the color.
// As above for POINTS, this normal is used for the lighting
// calculations of the LINES.
osg::Vec3Array* normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
linesGeom->setNormalArray(normals, osg::Array::BIND_OVERALL);
@@ -210,7 +219,7 @@ osg::Node* createScene()
linesGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
// set the normal in the same way color.
// Set the normal in the same way as the color (see note at POINTS, above).
osg::Vec3Array* normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
linesGeom->setNormalArray(normals, osg::Array::BIND_OVERALL);
@@ -255,7 +264,7 @@ osg::Node* createScene()
linesGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
// set the normal in the same way color.
// Set the normal in the same way as the color (see note at POINTS, above).
osg::Vec3Array* normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
linesGeom->setNormalArray(normals, osg::Array::BIND_OVERALL);
@@ -273,22 +282,20 @@ osg::Node* createScene()
// now we'll stop creating separate normal and color arrays
// since we are using the same values all the time, we'll just
// share the same ColorArray and NormalArrays..
// Now we'll stop creating separate normal and color arrays.
// Since we are using the same values all the time, we'll just
// share the same ColorArray and NormalArrays.
// set the colors as before, use a ref_ptr rather than just
// Set the colors as before, use a ref_ptr rather than just
// standard C pointer, as that in the case of it not being
// assigned it will still be cleaned up automatically.
osg::ref_ptr<osg::Vec4Array> shared_colors = new osg::Vec4Array;
shared_colors->push_back(osg::Vec4(1.0f,1.0f,0.0f,1.0f));
// same trick for shared normal.
// Same trick for shared normal.
osg::ref_ptr<osg::Vec3Array> shared_normals = new osg::Vec3Array;
shared_normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
// Note on vertex ordering.
// According to the OpenGL diagram vertices should be specified in a clockwise direction.
// In reality you need to specify coords for polygons in a anticlockwise direction
@@ -510,10 +517,17 @@ osg::Node* createScene()
geode->addDrawable(polyGeom);
}
// Turn off the lighting on the geode. This is not required for setting up
// the geometry. However, by default, lighting is on, and so the normals
// above are used to light the geometry.
// - With lighting turned off, the geometry has the same color
// regardless of the angle you view it from.
// - With lighting turned on, the colors darken as the light moves
// away from the normal.
geode->getOrCreateStateSet()->setMode(GL_LIGHTING,
osg::StateAttribute::OFF | osg::StateAttribute::PROTECTED);
return geode;
} //createScene()
}
// define a node callback to animate a transform as a cycle along the y axis, between 0 and 2.0.
@@ -545,7 +559,7 @@ class MyTransformCallback : public osg::NodeCallback
float _angular_velocity;
}; //class MyTransformCallback
};
/// Create a quad that sits behind the geometry from createScene()
/// and shows the image from the OpenGL docs that geometry duplicates.
@@ -579,7 +593,7 @@ osg::Node* createBackground()
polyGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
// set the normal in the same way color.
// Set the normal in the same way as the color.
osg::Vec3Array* normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f,-1.0f,0.0f));
polyGeom->setNormalArray(normals, osg::Array::BIND_OVERALL);
@@ -598,7 +612,7 @@ osg::Node* createBackground()
// and use it to set texture unit 0.
polyGeom->setTexCoordArray(0,new osg::Vec2Array(numTexCoords,myTexCoords));
// well use indices and DrawElements to define the primitive this time.
// we'll use indices and DrawElements to define the primitive this time.
unsigned short myIndices[] =
{
0,
@@ -627,13 +641,13 @@ osg::Node* createBackground()
polyGeom->setStateSet(stateset);
// create the Geode (Geometry Node) to contain the quad's osg::Geometry
osg::Geode* geode = new osg::Geode();
// add the points geometry to the geode.
geode->addDrawable(polyGeom);
// Turn off the lighting (see note in createScene(), above).
geode->getOrCreateStateSet()->setMode(GL_LIGHTING,
osg::StateAttribute::OFF | osg::StateAttribute::PROTECTED);
@@ -643,7 +657,7 @@ osg::Node* createBackground()
transform->addChild(geode);
return transform;
} //createBackground()
}
int main(int, char **)
{
@@ -652,7 +666,7 @@ int main(int, char **)
root->addChild( createScene() );
root->addChild( createBackground() );
//osgDB::writeNodeFile(*root,"geoemtry.osgt");
//osgDB::writeNodeFile(*root,"geometry.osgt");
osgViewer::Viewer viewer;