added stars rendering in background

src/font/font-demo.cpp

@@ -8,14 +8,26 @@
 #include <sstream>
 #include <limits>
 
+/** Application parameters **/
+
 constexpr unsigned int WIDTH = 1920;
 constexpr unsigned int HEIGHT = 1080;
+constexpr unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
 constexpr bool OFFSCREEN = false;
 constexpr const char* OUTPUT_FILENAME = "font-demo.mkv";
 constexpr const int VA_HW_DEVICE_INDEX = 0;
 constexpr double FPS = 60;
 
+/** Visualization parameters **/
+
 constexpr float FONT_SIZE = 40.0f;
+constexpr float MAX_STAR_SIZE = 1.0f;
+constexpr int MIN_STAR_COUNT = 1000;
+constexpr int MAX_STAR_COUNT = 3000;
+constexpr float MIN_STAR_LIGHTNESS = 1.0f;
+constexpr int MIN_STAR_ALPHA = 5;
+// Intensity of glow defined by kernel size. The default scales with the image diagonal.
+constexpr int GLOW_KERNEL_SIZE = std::max(int(DIAG / 138 % 2 == 0 ? DIAG / 138  + 1 : DIAG / 138), 1);
 
 using std::cerr;
 using std::endl;
@@ -52,14 +64,14 @@ int main(int argc, char **argv) {
     cerr << "OpenGL Version: " << gl::get_info() << endl;
     cerr << "OpenCL Platforms: " << endl << cl::get_info() << endl;
 
-    //BGRA frame buffer and warped image
-    cv::UMat frameBuffer, warped;
-    //BGR video frame.
+    //BGRA
+    cv::UMat frameBuffer, stars, warped;
+    //BGR
     cv::UMat videoFrame;
 
     //The text to display
     string text = cv::getBuildInformation();
-    //Create a istringstream that we will read and the rewind. over again.
+    //Create a istringstream that we will read and then rewind. over again.
     std::istringstream iss(text);
     //Count the number of lines.
     off_t numLines = std::count(text.begin(), text.end(), '\n');
@@ -68,6 +80,34 @@ int main(int argc, char **argv) {
     vector<cv::Point2f> src = {{0,0},{WIDTH,0},{WIDTH,HEIGHT},{0,HEIGHT}};
     vector<cv::Point2f> dst = {{WIDTH/3,0},{WIDTH/1.5,0},{WIDTH,HEIGHT},{0,HEIGHT}};
     cv::Mat M = cv::getPerspectiveTransform(src, dst);
+    cv::RNG rng(cv::getTickCount());
+
+    //Activate the OpenCL context for OpenGL.
+    gl::bind();
+    //Begin a nanovg frame.
+    nvg::begin();
+    nvg::clear(0,0,0,1);
+    {
+        //draw stars
+        using kb::nvg::vg;
+        int numStars = rng.uniform(MIN_STAR_COUNT, MAX_STAR_COUNT);
+        for(int i = 0; i < numStars; ++i) {
+            nvgBeginPath(vg);
+            nvgStrokeWidth(vg, rng.uniform(0.5f, MAX_STAR_SIZE));
+            nvgStrokeColor(vg, nvgHSLA(0, 1, rng.uniform(MIN_STAR_LIGHTNESS, 1.0f), rng.uniform(MIN_STAR_ALPHA, 255)));
+            nvgCircle(vg, rng.uniform(0, WIDTH) , rng.uniform(0, HEIGHT), MAX_STAR_SIZE);
+            nvgStroke(vg);
+        }
+    }
+    //End a nanovg frame
+    nvg::end();
+
+    //Aquire frame buffer from OpenGL.
+    gl::acquire_from_gl(frameBuffer);
+    //Copy the star rendering.
+    frameBuffer.copyTo(stars);
+    //Release frame buffer to OpenGL.
+    gl::release_to_gl(frameBuffer);
 
     //Frame count.
     size_t cnt = 0;
@@ -76,15 +116,14 @@ int main(int argc, char **argv) {
 
     while (true) {
         y = 0;
-
-        //Activate the OpenCL context for OpenGL.
         gl::bind();
         //Begin a nanovg frame.
         nvg::begin();
-        //Clear the screen with black. The clear color can be specified.
-        nvg::clear();
+        //Clear the screen with black.
+        nvg::clear(0,0,0,0);
         {
             using kb::nvg::vg;
+            nvgBeginPath(vg);
             nvgFontSize(vg, FONT_SIZE);
             nvgFontFace(vg, "serif");
             nvgFillColor(vg, nvgHSLA(0.15, 1, 0.5, 255));
@@ -106,7 +145,7 @@ int main(int argc, char **argv) {
             for (std::string line; std::getline(iss, line); ) {
                 //Check if all yet-to-crawl lines have been skipped.
                 if(skipLines == 0) {
-                    //Check if the current lines fits in the page.
+                    //Check if the current line fits in the page.
                     if(((translateY + y) / FONT_SIZE) < pageLines) {
                         nvgText(vg, WIDTH/2.0, y, line.c_str(), line.c_str() + line.size());
                         y += FONT_SIZE;
@@ -135,10 +174,10 @@ int main(int argc, char **argv) {
         gl::acquire_from_gl(frameBuffer);
         //Pseudo 3D text effect.
         cv::warpPerspective(frameBuffer, warped, M, videoFrame.size(), cv::INTER_LINEAR, cv::BORDER_CONSTANT, cv::Scalar());
-        //Copy back to frame buffer
-        warped.copyTo(frameBuffer);
+        //Combine layers
+        cv::add(stars, warped, frameBuffer);
         //Color-conversion from BGRA to RGB. OpenCV/OpenCL.
-        cv::cvtColor(warped, videoFrame, cv::COLOR_BGRA2RGB);
+        cv::cvtColor(frameBuffer, videoFrame, cv::COLOR_BGRA2RGB);
         //Transfer buffer ownership back to OpenGL.
         gl::release_to_gl(frameBuffer);