Lens Flare Volume Shader

My RenderMan Study

Lens Flare Volume Shader

First, I observed 'Lens Flare' effect of Photoshop, and by utilizing a pixel-coordinates, I indicated on a table how flares change their positions with the movement of the lens center. And, using this data, I wrote the shader, KTlensflareV.sl. This is a volume shader, and calculates the positions of flares automatically.
Fig.1	Fig.2
Fig.1 is the 'Lens Flare' image of Photoshop. Fig.2 is the image of KTlensflareV.sl. Here is the RIB.

What settles the positions of flares is the center of a lens. I call it SunP in KTlensflareV.sl. By changing this parameter, the center of a lens can be moved. This parameter is a vector, also its coordinates is defined in '"camera" space'. In addtion, the intensity of lens light and lens sparkle can be controlled by the parameters Highlight_intensity and light_intensity. And in Fig.3 and Fig.4, we can see the effect of the sparkle parameter, lightscale.
Fig.3	Fig.4
lightscale in Fig.3 is set at "10", in Fig.4 is "20".

Here is the code,

lighttheta=noise(lightscale*lighttheta);
lighttheta=clamp(lighttheta,light_min,light_max);
lighttheta=(lighttheta-light_min)/(light_max-light_min);
lighttheta=lighttheta*pow(lightdis+1,-(light_roughness));
lighttheta*=light_intensity;
Ci=Oi*mix(Ci,lightcolor,lighttheta);

KTlensflareV.sl can calculate 13 flares. Naturally, this shader has the parameters for opasity(as the float a of mix()), color, size (as the radius of a flare), and type for all of the 13 flares. The flare type in Fig.5 is 'clamp', in Fig.6 is 'sine', in Fig.7 is 'step', and in Fig.8 is 'specular'.
Fig.5	Fig.6	Fig.7	Fig.8

Here is the example code,

max_ring_sL1_1=0.98;
r=judge_sLP1_1/ring_sL1_1;
dis=r;
r=clamp(r,0,max_ring_sL1_1);
r/=max_ring_sL1_1; if (type_s1_1=="clamp") {: r=r-smoothstep(max_ring_sL1_1,1,dis);
}
if (type_s1_1=="sine") {: r=sin(r*(PI/2));; r=r-smoothstep(max_ring_sL1_1,1,dis);
}
if (type_s1_1=="step") {: r=1-smoothstep(max_ring_sL1_1,1,dis);
}
if (type_s1_1=="specular") {: r=pow(1+dis,s_roughness);
}
r*=max_mix_sL1_1;
ci_s1_1=mix(Ci,cs_s1_1,r);

max_mix_sL1_1 --> a opasity parameter (in the case of Fig.5-Fig.8, "0.5");
cs_s1_1 --> a color parameter (in the case, "0.74 1 0.87");
ring_sL1_1 --> a size parameter (in the case, "0.5");
type_s1_1 --> a type parameter;

Also, the size parameter (as mentioned above, the radius of a flare) can be regarded and set as a size (or unit) of 'ScreenWindow' in RIB. This is because KTlensflareV.sl has the parameter *fov* which needs to be set at the value of "fov" in RIB.

Here is the code,

r_unit=tan(radians(fov/2));
judgeS=distance(SWP,SWSunP)/r_unit;
judgeLP1=distance(SWP,SWLensP1)/r_unit;
judgeLP2=distance(SWP,SWLensP2)/r_unit;
judgeLP3=distance(SWP,SWLensP3)/r_unit;
judgeLP4=distance(SWP,SWLensP4)/r_unit;
judgeLP5=distance(SWP,SWLensP5)/r_unit;
judgeLP6=distance(SWP,SWLensP6)/r_unit;

SWP, SWSunP --> "P", *SunP* that were translated on ScreenWindow;
SWLensP1,..,SWLensP6 --> the points of flares that were calculated automatically first and translated on ScreenWindow;
judgeS --> a distance from SWP to SWSunP ,which was normalized by *fov*;

After this,

if (judgeS<*the size parameter of a flare*) {: /*(as mentioned above, give opacity, color, and type.)*/
}
......

fov as well as "fov" in RIB In Fig.9 - Fig.11 is set at "60", also 'flameaspect' is 2. The size paramete of a flare In Fig.9 and Fig.10 is set at "0.5", In Fig.11 is "1". 'ScreenWindow' in RIB In Fig.9 and Fig.11 is '-2 2 -1 1' (i.e. the size is 42), In Fig.10* is half (i.e. 2*1).
Fig.9	Fig.10	Fig.11

Last but not least, KTlensflareV.sl supports 'fog' effect when the string parameter *fog* is "on". By the way, 'fog.sl' should be the following, I think...

fog_d=1-exp(-length(I)/distance);
Ci=Oi*mix(Ci,background,fog_d);