martin-karl lefrançois may 2017 - nvidia...4 irradiance irradiance is a measurement of solar power...
TRANSCRIPT
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Martin-Karl Lefrançois May 2017
LIGHT BAKING WITH IRAY
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LIGHT BAKING
Computing and storing the information of complex lighting to be used in a real time environment. Freezing lights information and storing the data that paint how the light rays bounce around static geometry. Caching pre-calculated lighting information in textures or per-vertex or some other form to recreate the lighting in real time.
What is it?
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IRRADIANCE
The act of irradiating; emission of rays of light. That which irradiates or is irradiated. The radiant power received by unit area of surface (physics)
Source: Wiktionary
What is Irradiance
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IRRADIANCE
Irradiance is a measurement of solar power and is defined as the rate at which solar energy falls onto a surface.
Intensity of Light
"irradiance" and "intensity of light" are the same
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TOOLS FOR MEASURING IRRADIANCE
Light meter / Exposure Meter An instrument that measures the intensity of the light reflected from or falling on a subject Calculates the optimum exposure depending on the film speed.
Measuring light intensity
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LIGHT METER / LUX METER
Lux meter for measuring illuminances. It is equal to one lumen per square meter.
Measuring Brightness
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DIFFUSE LIGHTING
Lambert's cosine law in its reversed form (Lambertian reflection) implies that the apparent brightness of a Lambertian surface is proportional to the cosine of the angle between the surface normal and the direction of the incident light.
Lambertian reflectance
Eθ = E i cos(θ )Cosine Law:
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LIGHTS
for(i=0;i<n_lights;++i)result+=lightContribution(L[i],N)*diffuse_color;
ColorlightContribution(light&L,vec3normal){returnL.color*dot(L.direction,normal);//-shadow,-AO,…}
Diffuse lighting
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LIGHTS
Colorall_lights(0,0,0)for(i=0;i<n_lights;++i)all_lights+=lightContribution(L[i],N);result+=all_lights*diffuse_color
Total contributions
Lci (Ldi i N )i∑
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LIGHTS
Environment High Dynamic Range Image (HDRi) Sun & Sky
Implicit Lights Point, spot, .. Area: sphere, rectangle, ..
Emissive Objects Geometry emitting some energy
Various sources of energy
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IRAY PHOTOREAL
Iray Photoreal Path tracer Physically based
MDL (Material Definition Language) Define the properties of the material Absorption, reflectivity Emissivity
Implementing Light Baking
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LIGHT BAKING
Gathering lighting effect from ray tracer to realtime • Emission from the Sun & Sky and
other HDRi • Lights and area lights • Bouncing light (Global illumination) • Shadows and ambient occlusion • LPE compatible • Using MDL
Adding all incoming light to a light map (texture)
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LIGHT PROBESSampling the Hemisphere
Sampling the hemisphere for all light contribution defined by a point and a normal
Lci (Ldi i N )i∑
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LIGHT BAKING
Irradiance probes are used to render the irradiance at certain locations in the scene. Orientation of the camera is irrelevant
Irradiance Probes (capturing elements)
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LIGHT BAKINGApplying on Object
Use light probes and place them on the surface of the object
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LIGHT BAKING
Sampling the object in 3D space for each texel.
Sampling the object
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LIGHT BAKING
For each texel, add a light probe
Irradiance Probes
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LIGHT BAKING
Rasterizing all triangles in the UV domain - Output position and normal
Finding 3D position of each texel
Position Normal
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UV BAKING
Vertex: gl_Position = vec4(texCoord, 1) * 2.0 - 1.0;
Fragment: fColor1 = vec4(varWorldPos, 1.0); fColor2 = vec4(varNormal, 1.0);
GLSL for UV baking
Position Normal
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LIGHT BAKING
Extract all points and normals Construct a list of irradiance probes Render
Convert to Irradiance Probes
Lp = {{p0,n0}, {p1,n1}, {p2,n2},…}
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LIGHT BAKING
Render using ‘iray' No tonemapper RGB floating point to receive the irradiance values Use values to put in an image at the earlier extracted positions
Render
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LIGHT BAKINGDifferent resolutions
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LIGHT BAKINGResult on Object
Without and with light map texture
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LIGHTING
vec4cc=color;if(has_texture){//Ajdustingthetexturetolinearspacecc=pow(texture(tex,varTexCoord0.xy),vec4(2.2));}fragcolor=cc*texture(lbk_tex,varTexCoord1.xy);
GLSL Fragment for lighting
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LIGHT BAKING ISSUESSeam and borders
Fixed by enlarging the contour
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LIGHT BAKINGMissing Texels
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LIGHT BAKINGRemoving some noise with Median Blur
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LIGHT BAKING
512x512, 100 iterations 1,4 seconds
18 million rays/seconds
Speed
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DEMOIray and Live
Iray 2000 iterations Live @60Hz
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EXTRA
Light Path Expression One light map per group of lights
L.*’light_group1’I : Path from a light source to the irradiance point, bounce n-times and touch one of the light which is part of group1.
Avoid objects to be part of the lighting contribution: L.*[^’obj1’]I : Any path that goes from any light to the irradiance point, but not touching the object obj1.
LPE
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GLOSSINESS
Compute the incoming light from dependent direction. Store the value with the incoming direction and use it for glossy light reflection.
Angle dependent illumination
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NEXT
Multisampling to cover the entire area of the texel A radius to the light probe could be better
Enhancement
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QUESTIONS?
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THANKS !