Refine xyY conversions for better robustness and code clarity

Improve floating-point safety by using epsilon-based checks (< 1e-10) instead of exact zero comparisons in division guards. Use clamp_rgb for intermediate RGB clamping in xyy_to_rgb for consistency and cleaner code.

Author: blueyetisoftware

color/core/rgb_to_xyy.lua

@@ -54,7 +54,7 @@ local function rgb_to_xyy(red, green, blue)
 
     -- Fix: Check for X + Y + Z == 0 to avoid division by zero (ST bug)
     local sum = X + Y + Z
-    if sum == 0 then
+    if sum < 1e-10 then  -- Use epsilon for floating-point safety
         return 0, 0, 0
     end
 

color/core/xyy_to_rgb.lua

@@ -50,13 +50,11 @@ local function xyy_to_rgb(x, y, Y)
     local b = X * M[3][1] + Y * M[3][2] + Z * M[3][3]
 
     -- Clamp to [0,1] for gamut
-    r = r < 0 and 0 or r > 1 and 1 or r
-    g = g < 0 and 0 or g > 1 and 1 or g
-    b = b < 0 and 0 or b > 1 and 1 or b
+    r, g, b = clamp_rgb(r, g, b)
 
     -- Fix: Check for max_rgb == 0 to avoid division by zero (ST bug)
     local max_rgb = math.max(r, g, b)
-    if max_rgb == 0 then
+    if max_rgb < 1e-10 then  -- Use epsilon for floating-point safety
         return 0, 0, 0
     end