QSGMaterial Class

Detailed Description

The QSGMaterial, QSGMaterialShader and QSGMaterialRhiShader subclasses form a tight relationship. For one scene graph (including nested graphs), there is one unique QSGMaterialShader or QSGMaterialRhiShader instance which encapsulates the shaders the scene graph uses to render that material, such as a shader to flat coloring of geometry. Each QSGGeometryNode can have a unique QSGMaterial containing the how the shader should be configured when drawing that node, such as the actual color to used to render the geometry.

QSGMaterial has two virtual functions that both need to be implemented. The function type() should return a unique instance for all instances of a specific subclass. The createShader() function should return a new instance of QSGMaterialShader or QSGMaterialRhiShader, specific to that subclass of QSGMaterial.

A minimal QSGMaterial implementation could look like this:

 class Material : public QSGMaterial
 {
 public:
     QSGMaterialType *type() const { static QSGMaterialType type; return &type; }
     QSGMaterialShader *createShader() const { return new Shader; }
 };

This is suitable only for the OpenGL-based, traditional renderer of the scene graph. When using the new, graphics API abstracted renderer, materials must create QSGMaterialRhiShader instances instead, or in addition:

 class Material : public QSGMaterial
 {
 public:
     Material() { setFlag(SupportsRhiShader, true); }
     QSGMaterialType *type() const { static QSGMaterialType type; return &type; }
     QSGMaterialShader *createShader() {
         if (flags().testFlag(RhiShaderWanted)) {
             return new RhiShader;
         } else {
             // this is optional, relevant for materials that intend to be usable with the legacy OpenGL renderer as well
             return new Shader;
         }
     }
 };