See create_cdf and create_pdf for more information.
int sample_cdf(float cdf[], float uniform_rand)
Returns the index of the sampled CDF.
void sample_cdf(float cdf[], float uniform_rand, int &index, float &x)
void sample_cdf(float cdf[], float uniform_rand, int &index, float &x, float &pdf)
Writes the index of the sampled CDF and extra information to output arguments.
cdf
The CDF to sample from (created with create_cdf).
uniform_rand
A uniform random variable (must be in range <0,1>).
index
The function writes the index of the CDF element that was sampled to this variable.
x
The function writes the coordinate of the CDF element that was sampled to this variable.
pdf
The function writes the PDF of the CDF element that was sampled to this variable.
Examples
CDFs are useful when sampling from distributions. For example, a CDF of light source power could be created. This would allow sampling of lights with a probability based on power. This is an example of a discrete CDF, where sampling selects among a fixed set of probabilities. Such a CDF could be created as follows:
// Iterate over all lights, sampling their power int[] li = getlights(); float values[]; resize(values, len(li)); int nsamples = 256; int sid = israytrace ? SID : newsampler(); vector s, pos, clr; float scale; for (int i = 0; i < len(li); i++) { for (int j = 0; j < nsamples; j++) { nextsample(sid, s.x, s.y, "mode", "nextpixel"); sample_light(li[i], P, s, Time, pos, clr, scale); values[i] += luminance(clr); } values[i] /= nsamples; } // Create a CDF of the power distribution float cdf[] = create_cdf(values); // Randomly select a light based on power distribution nextsample(sid, s.x, s.y, "mode", "nextpixel"); int index = 0; sample_cdf(cdf, s.x, index); // Do something with the selected light // li[index] ...
| See also | |
| bsdf | |
| pbr |
|
| sampling |