Avoid the case c0 == c1 when encoding

This case may break buggy decoders.

diff --git a/s2tc_algorithm.cpp b/s2tc_algorithm.cpp
index 9aca027..adf783c 100644 (file)
--- a/s2tc_algorithm.cpp
+++ b/s2tc_algorithm.cpp
@@ -59,6 +59,10 @@ namespace
        {
                return (color_t) {i >> 3, i >> 2, i >> 3};
        }
+       inline bool operator==(const color_t &a, const color_t &b)
+       {
+               return a.r == b.r && a.g == b.g && a.b == b.b;
+       }
        inline bool operator<(const color_t &a, const color_t &b)
        {
                signed char d;
@@ -71,6 +75,56 @@ namespace
                d = a.b - b.b;
                return d < 0;
        }
+       inline color_t &operator--(color_t &c)
+       {
+               if(c.b > 0)
+               {
+                       --c.b;
+               }
+               else if(c.g > 0)
+               {
+                       c.b = 31;
+                       --c.g;
+               }
+               else if(c.r > 0)
+               {
+                       c.b = 31;
+                       c.g = 63;
+                       --c.r;
+               }
+               else
+               {
+                       c.b = 31;
+                       c.g = 63;
+                       c.r = 31;
+               }
+               return c;
+       }
+       inline color_t &operator++(color_t &c)
+       {
+               if(c.b < 31)
+               {
+                       ++c.b;
+               }
+               else if(c.g < 63)
+               {
+                       c.b = 0;
+                       ++c.g;
+               }
+               else if(c.r < 31)
+               {
+                       c.b = 0;
+                       c.g = 0;
+                       ++c.r;
+               }
+               else
+               {
+                       c.b = 0;
+                       c.g = 0;
+                       c.r = 0;
+               }
+               return c;
+       }
        template<> struct color_type_info<color_t>
        {
                static const color_t min_value;
@@ -613,6 +667,21 @@ namespace
                                break;
                        out2.clear();
                }
+
+               if(a1 == a0)
+               {
+                       if(a0 == 255)
+                               --a1;
+                       else
+                               ++a1;
+                       for(int i = 0; i < 16; ++i) switch(out.get(i))
+                       {
+                               case 1:
+                                       out.set(i, 0);
+                                       break;
+                       }
+               }
+
                if(a1 < a0)
                {
                        std::swap(a0, a1);
@@ -645,6 +714,20 @@ namespace
                s2tc_try_encode_block<unsigned char, int, 3, false, true, 6>(out, r2, alpha_dist, in, iw, w, h, ramp);
                r2.evaluate(a0, a1);
 
+               if(a1 == a0)
+               {
+                       if(a0 == 255)
+                               --a1;
+                       else
+                               ++a1;
+                       for(int i = 0; i < 16; ++i) switch(out.get(i))
+                       {
+                               case 1:
+                                       out.set(i, 0);
+                                       break;
+                       }
+               }
+
                if(a1 < a0)
                {
                        std::swap(a0, a1);
@@ -707,6 +790,18 @@ namespace
                                break;
                        out2.clear();
                }
+
+               if(c0 == c1)
+               {
+                       if(c0 == color_type_info<color_t>::max_value)
+                               --c1;
+                       else
+                               ++c1;
+                       for(int i = 0; i < 16; ++i)
+                               if(!(out.get(i) == 1))
+                                       out.set(i, 0);
+               }
+
                if(have_trans ? c1 < c0 : c0 < c1)
                {
                        std::swap(c0, c1);
@@ -727,6 +822,18 @@ namespace
                s2tc_evaluate_colors_result_t<color_t, bigcolor_t, 1> r2;
                s2tc_try_encode_block<color_t, bigcolor_t, 2, have_trans, false, 2>(out, r2, ColorDist, in, iw, w, h, ramp);
                r2.evaluate(c0, c1);
+
+               if(c0 == c1)
+               {
+                       if(c0 == color_type_info<color_t>::max_value)
+                               --c1;
+                       else
+                               ++c1;
+                       for(int i = 0; i < 16; ++i)
+                               if(!(out.get(i) == 1))
+                                       out.set(i, 0);
+               }
+
                if(have_trans ? c1 < c0 : c0 < c1)
                {
                        std::swap(c0, c1);
@@ -893,6 +1000,26 @@ namespace
                                reduce_colors_inplace_2fixpoints(ca, n, m, alpha_dist, (unsigned char) 0, (unsigned char) 255);
                }
 
+               // equal colors are BAD
+               if(c[0] == c[1])
+               {
+                       if(c[0] == color_type_info<color_t>::max_value)
+                               --c[1];
+                       else
+                               ++c[1];
+               }
+
+               if(dxt == DXT5)
+               {
+                       if(ca[0] == ca[1])
+                       {
+                               if(ca[0] == 255)
+                                       --ca[1];
+                               else
+                                       ++ca[1];
+                       }
+               }
+
                switch(dxt)
                {
                        case DXT1: