What is "The Raster Engine"
we talk about Raster paint Engine in Qt, can any of you experts let me know what does this mean. I will appreciate if you can point me to some article which talks about this what exactly is Qt's Raster Engine.
How it is different from others like GDI and X11 and OpenGL
The "raster" engine is one of the QPaintEngines available inside Qt. When you paint on a QPaintDevice, that device must provide an engine to paint on it.
The raster is a software engine which backs painting on QImages and QWidgets/QPixmaps on Windows (and/or other systems when you set the raster graphicssystem; it'll be the default in 4.8).
X11 and OpenGL are implemented in other QPaintEngines, and used respectively by QWidget/QPixmap under X11 and QGLWidget/QGLPixelBuffer everywhere. (Actually, there are two OpenGL engines, but that's a different story).