[gimp] app: improve performance of HSV value mode

[N/A <ell src gnome org>]

commit bcb242df6482490eb613a97a2fb4c7de2e27f25e
Author: Ell <ell_se yahoo com>
Date:   Wed Mar 15 18:37:35 2017 -0400

    app: improve performance of HSV value mode
    
    No need to do full back and forth RGB/HSV conversions.

 .../layer-modes/gimpoperationlayermode.c           |   30 +++++++++++++------
 1 files changed, 20 insertions(+), 10 deletions(-)
---
diff --git a/app/operations/layer-modes/gimpoperationlayermode.c 
b/app/operations/layer-modes/gimpoperationlayermode.c
index 377a08b..ded2662 100644
--- a/app/operations/layer-modes/gimpoperationlayermode.c
+++ b/app/operations/layer-modes/gimpoperationlayermode.c
@@ -1909,19 +1909,29 @@ blendfun_hsv_value (const float *dest,
     {
       if (dest[ALPHA] != 0.0f && src[ALPHA] != 0.0f)
         {
-          GimpRGB dest_rgb = { dest[0], dest[1], dest[2] };
-          GimpRGB src_rgb  = { src[0], src[1], src[2] };
-          GimpHSV src_hsv, dest_hsv;
+          gfloat dest_v;
+          gfloat src_v;
 
-          gimp_rgb_to_hsv (&dest_rgb, &dest_hsv);
-          gimp_rgb_to_hsv (&src_rgb, &src_hsv);
+          dest_v = MAX (dest[0], dest[1]);
+          dest_v = MAX (dest_v, dest[2]);
 
-          dest_hsv.v = src_hsv.v;
-          gimp_hsv_to_rgb (&dest_hsv, &dest_rgb);
+          src_v  = MAX (src[0], src[1]);
+          src_v  = MAX (src_v, src[2]);
 
-          out[RED]   = dest_rgb.r;
-          out[GREEN] = dest_rgb.g;
-          out[BLUE]  = dest_rgb.b;
+          if (dest_v != 0.0f)
+            {
+              gfloat ratio = src_v / dest_v;
+              gint   c;
+
+              for (c = 0; c < 3; c++)
+                out[c] = dest[c] * ratio;
+            }
+          else
+            {
+              out[RED]   = src_v;
+              out[GREEN] = src_v;
+              out[BLUE]  = src_v;
+            }
         }
 
       out[ALPHA] = src[ALPHA];