Using PNG background texture

* JPG version fails to load on some Macs and on Windoze (static build)
* TODO: try alternatives to reduce the PNG size or fix the root cause

src/pulsaranimationwidget.cpp

@@ -196,7 +196,7 @@ void PulsarAnimationWidget::initializeGL()
     }
 
     // prepare and check background texture
-    QImage backgroundTexture(":/textures/resources/texture_background_carina.jpg");
+    QImage backgroundTexture(":/textures/resources/texture_background_carina.png");
     if(backgroundTexture.width() != backgroundTexture.height()) {
     	qWarning() << msgShape.arg(tr("Background"));
     }
@@ -215,7 +215,7 @@ void PulsarAnimationWidget::initializeGL()
 
     // bind textures
     m_pulsarTexture = bindTexture(pulsarTexture, GL_TEXTURE_2D, GL_RGBA);
-    m_backgroundTexture = bindTexture(backgroundTexture, GL_TEXTURE_2D, GL_RGB);
+    m_backgroundTexture = bindTexture(backgroundTexture, GL_TEXTURE_2D, GL_RGBA);
 
     // use mipmapped textures
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

src/pulsatingscience.qrc

@@ -13,7 +13,7 @@
     <file>resources/pulsatingscience_de.qm</file>
   </qresource>
   <qresource prefix="textures" >
-    <file>resources/texture_background_carina.jpg</file>
+    <file>resources/texture_background_carina.png</file>
     <file>resources/texture_pulsar.png</file>
   </qresource>
 </RCC>