Environment Maps

[Robadob]

This follows on from Materials/Lighting. Hopefully a quick branch for some nice resulting visuals.

• Allow binding of static environment map to Models/Materials (e.g. the skybox).
• Update material shaders to utilise reflection, refraction and environment maps.
• The ability to generate dynamic environment (cube) maps, per model or similar.

https://learnopengl.com/Advanced-OpenGL/Cubemaps (high level pure reflection example + refraction) https://en.wikibooks.org/wiki/GLSL_Programming/GLUT/Glossy_Textures (Introduced shininessStrength, as a multiplier for level of glossiness, encoded in alpha channel of texture).

To access reflection sample we use

//Convert reflection vector back to world space
reflected = vec3(inverse(_viewMat) * vec4(reflected, 0.0));
//Sample environment map in that direction
frag_colour = texture(t_reflection, reflected);

Alternatively, replace reflect() with refract() to simulate light moving through materials of different light properties. Utilising the refractive index. This makes models appear transparent, rather than reflective/glossy. Refraction should actually occur twice (as the light exits the material too), however this is harder to achieve within complex models.

Material	Refractive Index
Air	1.00
Water	1.33
Ice	1.309
Glass	1.52
Diamond	2.42

More@wikipedia

Ratio is calculated as source/destination.

Need to find more info on doing dynamic cubemaps, seen suggestion that rendering over a static skybox gives fastest results. Try this, although I can't see from their example how/if view matrix is transformed. Otherwise seems sensible. Another attempt here.

[Robadob]

Dynamic environment mapping now implemented in branch.

• [x] Test integration with BasicScene
• [ ] Test integration with MultiPassScene
• [x] Add origin offset to dynamic maps.
• [x] Add single surface refraction
• [x] Make use of transparent color material property
• [x] Ensure Entity dynamic env maps continue to work after reload
• [ ] Ensure Model dynamic env maps continue to work after reload
• [ ] Allow BasicScene to Blit the skybox instead of render?
  • Could even cache a render of all static components and depth, but that seems a bit advanced for our 'requirements'
• [ ] Include reflectivity handling in all Material shaders (dev has been completed in material_phong.frag)
• [x] Name the env map texture as envmap in shader (it's currently mislabelled reflection map)

[Robadob]

Fixed the deer lighting issue on latest commit.

Fixed Bob model default shader reload bug, might not track custom textures but this isn't something I've really tested on Model's yet anyway (do they even support it??).

[Robadob]

This appears to have a clear example of using Fresnels law for localised reflection.

uniform float Kr, // intensity of reflection
uniform float KrMin, // typical: 0.05 * Kr
uniform float FresExp, // typical: 5.0

  float3 Nu = normalize(IN.LightingNormal);
   float3 Vu = normalize(IN.LightingEyeVec);
  float vdn = dot(Vu, Nb); // or "Nu" if unbumped - see text
   float fres = KrMin + (Kr - KrMin) * pow((1.0 - abs(vdn)), FresExp);
  float3 reflVect = normalize(reflect(Vu, Nb)); // yes, normalize
// now use the new intersection location as the 3D direction
    reflColor = fres * texCUBE(EnvMap, reflVect);

  float4 result = SurfColor * reflColor;

More: https://chetanjags.wordpress.com/2015/08/26/image-based-lighting/ https://learnopengl.com/PBR/IBL/Specular-IBL