BRDF Explorer GUI

[manhnt9]

We can discuss and update progress on GUI development of BRDF Explorer extension here.

Developer: @Florastamine Adviser: @manhnt9 @devshgraphicsprogramming

Screenshots: to be updated when there's new progress from @Florastamine

Notes after discussion on Discord:

• Enable sRGB textures in CEGUI
• Color Picker: CEGUI's class, add color wheel if possible (low priority)
• File dialog: nativefiledialog library
• Theme: TaharezLook or AlfiskoSkin

Task list made by @Florastamine:

• [x] Remove the loaded resource paths list box
• [x] Change light & material parameters into sliders
• [x] Review slider ranges
• [x] Fix roughness sliders & add a lock checkbox
• [x] Make the AO & bumpmapping thumbnail click-able
• [x] Add an option to select between tweakable shader constants or from texture
• [x] Improve the texture preview window
• [x] Transparent panels & make the GUI optionally toggle-able
• [x] Replace WindowsLook theme with a better fit one (preferably dark, blue-ish)

How to integrate CEGUI into IrrBAW:

• Study Example 33 to understand extension architecture
• Write a CEGUI manager class as extension
• Fork IrrBAW, checkout branch stable-ish
• Create another IrrBAW example for BRDR Explorer

How to render CEGUI with IrrBAW: Use this code snippet for GUI rendering

auto renderState = irr::video::COpenGLState::collectGLState();
irr::video::COpenGLState guiState;
executeGLDiff(guiState.getStateDiff(renderState));  
CEGUI::System::getSingleton().renderAllGUIContexts();
executeGLDiff(renderState.getStateDiff(irr::video::COpenGLState::collectGLState()));

See more about how to use IrrBAW's OpenGL state manager at this file.

Notes:

• Only use stable-ish branch, will try to merge in to unstable master later (need DevSH's advices)
• Commit with CEGUI datafiles (filter out what is used)