utils: document horrible value bug discovered in remap[T]/5

lib/color.v

@@ -365,7 +365,9 @@ pub fn (c &ColorHSV) as_rgb() Color {
 		else {}
 	}
 
-	// println('RGB: ${r} ${g} ${b} RGB*255: ${r * 255} ${g * 255} ${b * 255} ')
+	// println(utils.remap(f32(c.h), 0, 360, 0, 1))
+	// println('HSV: ${h} ${s} ${v} I ${i} FPQT: ${f} ${p} ${q} ${t}')
+	// println('RGBA: ${r} ${g} ${b} ${a} RGB*255(A): ${r * 255} ${g * 255} ${b * 255} (${a})')
 
 	return Color{
 		r: u8(r * 255)

utils/utils.v

@@ -11,27 +11,40 @@ pub const stdout_is_a_pipe = (os.is_atty(1) == 0)
 
 @[inline]
 pub fn remap[T](value T, min T, max T, new_min T, new_max T) T {
-	return (((value - min) * (new_max - new_min)) / (max - min)) + new_min
+	// BUG: This is carefully crafted like this because 2 hours of debugging led to this obscure corner case
+	// I think it is a "regression" (maybe not) with V's generics (cgen?, cast?, parenthesis?)
+	// `return (((value - min) * (new_max - new_min)) / (max - min)) + new_min` <- this version, incl. return T(...)
+	// consistently returned "0.0" until the temp var `r` was used... and I could NOT reduce the scenario.
+	// It was discovered while rewriting a function to procedurally generate shade colors (HSV -> RGB) for some bushes...
+	// The nasty thought is that something using T *elsewhere* can someday do the same in some unrelated context... nightmare
+	r := T((((value - min) * (new_max - new_min)) / (max - min)) + new_min)
+	return r
+	// return (((value - min) * (new_max - new_min)) / (max - min)) + new_min
+	// The above yields red bushes in small_world with just `v run`...
 }
 
 @[inline]
 pub fn remap_u8_to_f32(value u8, min u8, max u8, new_min f32, new_max f32) f32 {
-	return f32((((value - min) * (new_max - new_min)) / (max - min)) + new_min)
+	r := f32((((value - min) * (new_max - new_min)) / (max - min)) + new_min)
+	return r
 }
 
 @[inline]
 pub fn remap_f32_to_u8(value f32, min f32, max f32, new_min u8, new_max u8) u8 {
-	return u8((((value - min) * (new_max - new_min)) / (max - min)) + new_min)
+	r := u8((((value - min) * (new_max - new_min)) / (max - min)) + new_min)
+	return r
 }
 
 @[inline]
 pub fn lerp[T](x T, y T, s T) T {
-	return x + s * (y - x)
+	r := T(x + s * (y - x))
+	return r
 }
 
 @[inline]
 pub fn clamp[T](val T, min T, max T) T {
-	return mth.min(mth.max(val, min), max)
+	r := T(mth.min(mth.max(val, min), max))
+	return r
 }
 
 // loop_f32 loops a continious `value` in the range `from`,`to`.