# LightRampAttrib¶

class LightRampAttrib

Bases: RenderAttrib

A Light Ramp is any unary operator that takes a rendered pixel as input, and adjusts the brightness of that pixel. For example, gamma correction is a kind of light ramp. So is HDR tone mapping. So is cartoon shading. See the constructors for an explanation of each kind of ramp.

Inheritance diagram

enum LightRampMode
enumerator LRT_default = 0
enumerator LRT_identity = 1
enumerator LRT_single_threshold = 2
enumerator LRT_double_threshold = 3
enumerator LRT_hdr0 = 4
enumerator LRT_hdr1 = 5
enumerator LRT_hdr2 = 6
static int get_class_slot(void)
static TypeHandle get_class_type(void)
PN_stdfloat get_level(int n) const

Returns the nth lighting level.

LightRampMode get_mode(void) const

Returns the LightRampAttrib mode.

PN_stdfloat get_threshold(int n) const

Returns the nth threshold level.

static ConstPointerTo<RenderAttrib> make_default(void)

Constructs a new LightRampAttrib object. This is the standard OpenGL lighting ramp, which clamps the final light total to the 0-1 range.

static ConstPointerTo<RenderAttrib> make_double_threshold(PN_stdfloat thresh0, PN_stdfloat lev0, PN_stdfloat thresh1, PN_stdfloat lev1)

Constructs a new LightRampAttrib object. This causes the luminance of the diffuse lighting contribution to be quantized using two thresholds:

if (original_luminance > threshold1) {
luminance = level1;
} else if (original_luminance > threshold0) {
luminance = level0;
} else {
luminance = 0.0;
}

static ConstPointerTo<RenderAttrib> make_hdr0(void)

Constructs a new LightRampAttrib object. This causes an HDR tone mapping operation to be applied.

Normally, brightness values greater than 1 cannot be distinguished from each other, causing very brightly lit objects to wash out white and all detail to be erased. HDR tone mapping remaps brightness values in the range 0-infinity into the range (0,1), making it possible to distinguish detail in scenes whose brightness exceeds 1.

However, the monitor has finite contrast. Normally, all of that contrast is used to represent brightnesses in the range 0-1. The HDR0 tone mapping operator ‘steals’ one quarter of that contrast to represent brightnesses in the range 1-infinity.

FINAL_RGB = (RGB^3 + RGB^2 + RGB) / (RGB^3 + RGB^2 + RGB + 1)

static ConstPointerTo<RenderAttrib> make_hdr1(void)

Constructs a new LightRampAttrib object. This causes an HDR tone mapping operation to be applied.

Normally, brightness values greater than 1 cannot be distinguished from each other, causing very brightly lit objects to wash out white and all detail to be erased. HDR tone mapping remaps brightness values in the range 0-infinity into the range (0,1), making it possible to distinguish detail in scenes whose brightness exceeds 1.

However, the monitor has finite contrast. Normally, all of that contrast is used to represent brightnesses in the range 0-1. The HDR1 tone mapping operator ‘steals’ one third of that contrast to represent brightnesses in the range 1-infinity.

FINAL_RGB = (RGB^2 + RGB) / (RGB^2 + RGB + 1)

static ConstPointerTo<RenderAttrib> make_hdr2(void)

Constructs a new LightRampAttrib object. This causes an HDR tone mapping operation to be applied.

Normally, brightness values greater than 1 cannot be distinguished from each other, causing very brightly lit objects to wash out white and all detail to be erased. HDR tone mapping remaps brightness values in the range 0-infinity into the range (0,1), making it possible to distinguish detail in scenes whose brightness exceeds 1.

However, the monitor has finite contrast. Normally, all of that contrast is used to represent brightnesses in the range 0-1. The HDR2 tone mapping operator ‘steals’ one half of that contrast to represent brightnesses in the range 1-infinity.

FINAL_RGB = (RGB) / (RGB + 1)

static ConstPointerTo<RenderAttrib> make_identity(void)

Constructs a new LightRampAttrib object. This differs from the usual OpenGL lighting model in that it does not clamp the final lighting total to (0,1).

static ConstPointerTo<RenderAttrib> make_single_threshold(PN_stdfloat thresh0, PN_stdfloat lev0)

Constructs a new LightRampAttrib object. This causes the luminance of the diffuse lighting contribution to be quantized using a single threshold:

if (original_luminance > threshold0) {
luminance = level0;
} else {
luminance = 0.0;
}