Additive blending for stars + add star parameters

data/assets/scene/digitaluniverse/stars.asset

@@ -29,7 +29,10 @@ local object = {
         Type = "RenderableStars",
         File = speck .. "/stars.speck",
         Texture = textures .. "/halo.png",
-        ColorMap = colorLUT .. "/colorbv.cmap"
+        ColorMap = colorLUT .. "/colorbv.cmap",
+        MagnitudeExponent = 19,
+        BillboardSize = 30,
+        Sharpness = 1.3
     },
     GuiPath = "/Milky Way/Stars"
 }

modules/space/rendering/renderablestars.cpp

@@ -329,7 +329,9 @@ void RenderableStars::deinitializeGL() {
 }
 
 void RenderableStars::render(const RenderData& data, RendererTasks&) {
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE);
     glDepthMask(false);
+
     _program->activate();
 
     glm::mat4 model =
@@ -373,6 +375,7 @@ void RenderableStars::render(const RenderData& data, RendererTasks&) {
     _program->deactivate();
 
     glDepthMask(true);
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 }
 
 void RenderableStars::update(const UpdateData&) {