Test - toggle the alpha value of featurenode symbols

cpp

#include <osgViewer/Viewer>
#include <osgEarth/Notify>
#include <osgEarth/EarthManipulator>
#include <osgEarth/ExampleResources>
#include <osgEarth/MapNode>
#include <osgEarth/FeatureNode>
#include <osgEarth/TMS>
#include <iostream>

using namespace osgEarth;
using namespace osgEarth::Util;

FeatureNode* feature_node = nullptr;
bool lowlight = false;

int
main(int argc, char** argv)
{
    osgEarth::initialize();
    osgViewer::Viewer viewer;
    viewer.setCameraManipulator(new EarthManipulator());

    auto mapnode = new MapNode();
    auto imagery = new TMSImageLayer();
    imagery->setURL("https://readymap.org/readymap/tiles/1.0.0/7/");
    mapnode->getMap()->addLayer(imagery);

    const char* style_xml = R"(
        <feature name="Testing">
            <srs>wgs84</srs>
            <geometry>
                POLYGON((-100 47, -100 49, -95 48, -96 45, -98 42))
            </geometry>
            <style type="text/css">
                Basic_Polygon_Style {
                    stroke: #ffff00;
                    stroke-width: 3px;
                    stroke-tessellation-size: 10km;
                    stroke-smooth: true;
                    fill: #00ff00;
                    text-content: "PRESS 'H' TO TOGGLE ME";
                    text-halo: #000000;
                    text-size: 48;
                    render-depth-offset: true;
                    render-max-tess-angle: 0.25;
                }
            </style>
        </feature>
    )";

    Config conf;
    conf.fromXML(std::istringstream(style_xml));            
    feature_node = new FeatureNode(conf.child("feature"), nullptr);
    mapnode->addChild(feature_node);

    viewer.setSceneData(mapnode);

    EventRouter::get(&viewer).onKeyPress(osgGA::GUIEventAdapter::KEY_H,
        [&](osg::View* view, float mx, float my)
        {
            lowlight = !lowlight;
            float alpha = lowlight ? 0.25f : 1.0f;

            // Make all other nodes transparent
            osgEarth::Style style = feature_node->getStyle();

            osgEarth::LineSymbol* lineSymbol =
                style.getSymbol<osgEarth::LineSymbol>();
            if (lineSymbol)
            {
                osgEarth::Color strokeColor = lineSymbol->stroke()->color();
                strokeColor.a() = alpha;
                lineSymbol->stroke()->color() = strokeColor;
            }

            osgEarth::PolygonSymbol* polygonSymbol =
                style.getSymbol<osgEarth::PolygonSymbol>();
            if (polygonSymbol)
            {
                osgEarth::Color fillColor = polygonSymbol->fill()->color();
                fillColor.a() = alpha;
                polygonSymbol->fill()->color() = fillColor;
            }

            osgEarth::TextSymbol* textSymbol =
                style.getSymbol<osgEarth::TextSymbol>();
            if (textSymbol)
            {
                osgEarth::Color textColor = textSymbol->fill()->color();
                textColor.a() = alpha;
                textSymbol->fill()->color() = textColor;
            }

            feature_node->setStyle(style);
            feature_node->dirty(); // Force redraw
        });

    return viewer.run();
}