Add a new optional parameter to colortemp() to control normalising

docs/builtins.md

@@ -441,15 +441,17 @@ MIT license.
 
 ## Color functions
 
-`colortemp(` *t* `)`
+`colortemp(` *t* [, *normalize*`=false` ] `)`
 : Return a 3-vector of *R*, *G* and *B* **linear sRGB** values for an
 approximation of the irradiance of a Planckian (blackbody) radiator at
 temperature *t*, scaled so that `colortemp(6503.5)` (the sRGB whitepoint
 correlated colour temperature) is close to `1;1;1`; the approximation only holds
 within the range *[1667,25000]* and, strictly speaking, values below 1900°K are
 outside the sRGB gamut; irradiance is proportional to the 4th power of the
 temperature, so the values are very small at low temperatures and become
-*significantly* larger at higher temperatures.
+*significantly* larger at higher temperatures. If the optional *normalize*
+parameter is `true` then the returned color will be normalized by dividing each
+channel by the larger of the 3.
 
 `hsl(` *h* `;` *s* `;` *l* `)`
 : Return a 3-vector of *R*, *G* and *B* in the range *[0,1]* from a 3-vector of

src/flitter/language/functions.pyx

@@ -1018,11 +1018,12 @@ def hsv(Vector color):
 
 @cython.cdivision(True)
 @cython.cpow(True)
-def colortemp(Vector t):
+def colortemp(Vector t, Vector normalize=false_):
     if t.numbers == NULL:
         return null_
     cdef int64_t i, n = t.length
-    cdef double T, T2, x, x2, y, X, Y, Z
+    cdef bint norm = normalize.as_bool()
+    cdef double T, T2, x, x2, y, X, Y, Z, r, g, b, c
     cdef Vector rgb = Vector.__new__(Vector)
     rgb.allocate_numbers(3*n)
     for i in range(n):
@@ -1042,9 +1043,17 @@ def colortemp(Vector t):
         Y = (max(0, t.numbers[i]) / 6503.5)**4
         X = Y * x / y
         Z = Y * (1 - x - y) / y
-        rgb.numbers[3*i] = max(0, 3.2406255*X - 1.537208*Y - 0.4986286*Z)
-        rgb.numbers[3*i+1] = max(0, -0.9689307*X + 1.8757561*Y + 0.0415175*Z)
-        rgb.numbers[3*i+2] = max(0, 0.0557101*X - 0.2040211*Y + 1.0569959*Z)
+        r = max(0, 3.2406255*X - 1.537208*Y - 0.4986286*Z)
+        g = max(0, -0.9689307*X + 1.8757561*Y + 0.0415175*Z)
+        b = max(0, 0.0557101*X - 0.2040211*Y + 1.0569959*Z)
+        if norm:
+            c = max(r, g, b)
+            r /= c
+            g /= c
+            b /= c
+        rgb.numbers[3*i] = r
+        rgb.numbers[3*i+1] = g
+        rgb.numbers[3*i+2] = b
     return rgb
 
 

tests/test_functions.py

@@ -687,6 +687,8 @@ def test_split(self):
 class TestColorFuncs(utils.TestCase):
     def test_colortemp(self):
         self.assertAllAlmostEqual(colortemp(Vector(6503.5)), Vector([1, 1, 1]), places=None, delta=0.05)
+        self.assertAllAlmostEqual(colortemp(Vector(1900)), Vector([0.0192550289, 0.0044625883, 0]), places=7)
+        self.assertAllAlmostEqual(colortemp(Vector(1900), Vector(1)), Vector([1, 0.0044625883/0.0192550289, 0]), places=7)
 
     def test_oklab(self):
         self.assertAllAlmostEqual(oklab(Vector([0, 0, 0])), Vector([0, 0, 0]), places=2)