Qt3D Painting

Porting between desktop OpenGL and embedded OpenGL/ES has traditionally been difficult. The usual sequence of operations for a drawing request in OpenGL consists of:

• Select an appropriate shader program, or fixed-function pipeline rendering options.
• Set or adjust the current projection and modelview matrices.
• Specify vertex, normal, texture co-ordinate, and other attribute arrays.
• Specify textures, variables, and other rendering objects needed by the shader program.
• Draw fragments: triangles, triangle fans, quads, etc.
• Disable the arrays, textures, and modes that were selected.

Desktop OpenGL, OpenGL/ES 1.1, and OpenGL/ES 2.0 all posses functionality for the above, but they are all different. OpenGL/ES 2.0 in particular presents unique problems because it lacks a fixed-function pipeline mode to perform common painting operations.

In Qt3D the QGLPainter class wraps OpenGL to present a consistent OpenGL painting API across all platforms. Shaders and fixed-function options are supplied as an instance of QGLAbstractEffect. Several built-in standard effects are provided for drawing with flat colors, material-based lighting, and simple texturing.