The goal of this project is to obtain a photo-realistinc rendering by using two main components: a realistic model of how light interacts with surfaces (PBR), and a model of illumination, which essentially captures the light in a real scene, and uses it to illuminate the scene (IBL). For the implementation, we have created a new material called PBR material which inherits form StandarMaterial, and the shader pbr.fs, that we assign to this material.

PBR MATERIAL material.cpp / material.h

TODO: setUniforms & setTextures

setUniforms Forcing slots manually

SHADER PBR.fs

The final color of the PBR material will be the addition of the punctual light and the environment light (using IBL). Therefore, the shader follows the next steps:

1. Create a PBR material and PBR vectors

2. Compute light equation vectors (N, L, V, R, H) as well as the dot products that we are going to need for the computations. N vec is computed using perturbNormal function provided with the normal_map in order to have a non-flat / irregular surface.

3. Initialize material properties:

• roughness - how irregular is a surface. Roughness varies in all the surface, we extract roughness from a roughness texture (u_roughness_map) and multiply by the roughness factor that is initialized as 1 by default.
• metalness - we extract the metalness from a metalness_map and multiply by a metalness factor that is also initialized as 1 by default.

For the previous ones, we take just one channel of the texture depending on the image we have and in which channel the information is located. TODO: en el cas del helmet no es el r channel, que dic?

• albedo - is the base color. We extract the albedo values from a 2D texture taking the rgb channels. Also, when doing computations with albedo is essential to do degamma to the color (we convert to linear before doing any computation).

• Opacity and Occlusion maps - if an opacity map exists, we also create a texture from it and extract one channel. Otherwise, the opacity will be 1.0. The same happens for the occlusion map. TODO VICTOR: repassa a ver si ho dic bé

• c_diff (diffuse colour/ diffuse albedo) - it is a vector of rgb -- For the diffuse color, we do a linear interpolation of a vec3 of zeros and the albedo color, over the metallicfactor. The absorption of color is represented by (1-metalness) * base color (albedo color). It will

• F0 (specular colour/specular albedo) - it is a linear interpolation of the albedo color and vec3 of 0.04, over the metallic factor. Unlike c_diff, the more specular the material, the more it reflects.

Next, the shader computes separately the direct and the indirect (environmental) lighting.

4. Compute the direct lighting (f = f_diffuse + f_specular) with the formulas

• f_diffuse : with the diffuse colour / pi (Lambertian diffusion equation) that give us a constant diffusion in every diretion of the half sphere.
• f_specular: this computation follows a more complex equation.

TODO: afegir formula??

• Fresnel function F(l,h): represents the fraction of light reflected from a flat surface. Depends on the incnident angle and reflective index. Computed with the specular color F0, using the following equation:

TODO: afegir formula

• Geometry function G(l,v,h): represents the proportion of microfacets with m = h that are neither shadowed nor masked. Depends on the roughness. Computed using the following equation:

TODO: afegir formula where the k is: TODO: afegir formula de la k

• Distribution function D(h): is the distribution of the normals of the micro-facets. Computed with the following equation: TODO: afegir formula de D i de alpha

Where alpha is: ...

Finally, computes direct lighting as diffuse + specular. We also multiply the result by the dot product between n and l (TODO: explicar why)

5. Compute indirect lighting using Image Based Lighting (IBL) The total environment light will be the sum of the diffuse environment light and the specular environment light. Each of them will have two components too (Radiance term and brdf term), from the Split Sum approximation of the rendering equation.

TODO:(Equation de Split Sume)

• diffuse IBL: we compute the radiance term using getReflectionColor with the normal and roughness = 1, as it will be completely diffuse. The other term, as it is the diffuse component, will be simply the albedo diffuse / PI (from the diffuse term of the BRDF)

• specular IBL: radiance term is

• Compute IBL color (diffuse IBL + specular IBL)

6. get Pixel color: get final color by adding IBL to the direct lighting (final_color = direct lighting + indirect lighting)

7. Apply tone-mapping for the HDR envoronments to transform the final light to how humans perceive it

8. Apply gamma correction (i.e. raise color intensities to 1/gamma) to display it in the monitor. As the monitors have non-linear color response with respect to raw values passed from the graphic card.