Improvement to Shadow System

Release 0.10.6

Better shadow system

• Shadow map filter can now be chosen in runtime. It current supports nearest and bilinear filter. More shadow smoothing techniques will be implemented in the future.
• Rename STPCascadedShadowMap to STPDirectionalLight to make it more general.
• Move shader storage buffer for shadow mapping from STPDirectionalLight to STPShadowPipeline which is a new class.
• STPSun is now also given choices for casting or not casting shadows.
• Add STPShadowInformation for sharing shadow map setting from STPShadowPipeline to various renderers.
• STPDirectionalLight now uses camera callback to determine if light space matrices are outdated and only recompute them (and flush the buffer) whenever necessary.

With the new system, the correct order for setting up a rendering pipeline is:

• Create light that casts shadows.
• Create STPShadowPipeline with an array of pointers to light that just created.
• Create all the rest of the scene including light that does not cast shadow and opaque object.
• Create STPScenePipeline with a pointer to STPShadowPipeline.

As now lights hold memory owned by the scene pipeline, make sure lights are not writting to the buffer after the dependent scene pipeline is destroyed.

General fixes and improvement

• Fix a potential undefined behaviour in terrain fragment shader for accessing array of bindless samplers in a non-uniform manner.
  • GL extension NV_gpu_shader5 is now required in order to run the program.
• Remove unnecessary extension directives from some shader codes.
• Move bindless shadow handle from individual shader to shader storage buffer to be shared among all renderers.
• STPCamera now allows registering as many listeners as user wants.
• STPScenePipeline now deregisters itself from camera callback at destruction.
• Fix an incorrect return value semantics in shadow map sampling shader. The return value of that function represents the light intensity instead of shadow intensity, or light intensity = 1.0 - shadow intensity.
• Rename rendering function name from operator() to some more concrete name like render().