[PATCH 2/5] wined3d: Improve the unsigned emulation of WINED3DFMT_R5G5_SNORM_L6_UNORM.

[Stefan Dösinger]

The R and G channels were swapped, and the masks were not correct
considering that we shifted the input value before adding the mask.

This emulation has precision problems by design. If this causes problems
in a game we can use an 8 bit per channel format instead of R5G6B5, but
so far I am not aware of any.
---
 dlls/wined3d/utils.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/dlls/wined3d/utils.c b/dlls/wined3d/utils.c
index 5f35ffb..791ddf3 100644
--- a/dlls/wined3d/utils.c
+++ b/dlls/wined3d/utils.c
@@ -294,25 +294,29 @@ static void convert_r5g5_snorm_l6_unorm(const BYTE *src, BYTE *dst, UINT src_row
         UINT dst_row_pitch, UINT dst_slice_pitch, UINT width, UINT height, UINT depth)
 {
     unsigned int x, y, z;
-    const WORD *Source;
+    unsigned char r_in, g_in, l_in;
+    const unsigned short *texel_in;
+    unsigned short *texel_out;
 
+    /* Emulating signed 5 bit values with unsigned 5 bit values has some precision problems by design:
+     * E.g. the signed input value 0 becomes 16. GL normalizes it to 16 / 31 = 0.516. We convert it
+     * back to a signed value by subtracting 0.5 and multiplying by 2.0. The resulting value is
+     * ((16 / 31) - 0.5) * 2.0 = 0.032, which is quite different from the intended result 0.000. */
     for (z = 0; z < depth; z++)
     {
         for (y = 0; y < height; y++)
         {
-            unsigned short *Dest_s = (unsigned short *) (dst + z * dst_slice_pitch + y * dst_row_pitch);
-            Source = (const WORD *)(src + z * src_slice_pitch + y * src_row_pitch);
+            texel_out = (unsigned short *) (dst + z * dst_slice_pitch + y * dst_row_pitch);
+            texel_in = (const unsigned short *)(src + z * src_slice_pitch + y * src_row_pitch);
             for (x = 0; x < width; x++ )
             {
-                short color = (*Source++);
-                unsigned char l = ((color >> 10) & 0xfc);
-                        short v = ((color >>  5) & 0x3e);
-                        short u = ((color      ) & 0x1f);
-                short v_conv = v + 16;
-                short u_conv = u + 16;
-
-                *Dest_s = ((v_conv << 11) & 0xf800) | ((l << 5) & 0x7e0) | (u_conv & 0x1f);
-                Dest_s += 1;
+                l_in = (*texel_in & 0xfc00) >> 10;
+                g_in = (*texel_in & 0x03e0) >> 5;
+                r_in = *texel_in & 0x001f;
+
+                *texel_out = ((r_in + 16) << 11) | (l_in << 5) | (g_in + 16);
+                texel_out++;
+                texel_in++;
             }
         }
     }
-- 
2.3.0