From 4482cb3e406b4f3a69670f37318f3f8ca4299f24 Mon Sep 17 00:00:00 2001
From: Chuck Walbourn <chuckw@windows.microsoft.com>
Date: Sun, 13 Mar 2022 14:52:34 -0700
Subject: [PATCH] Fixed bug in CPU BC6H compressor if none of the pixel values
 fall into the SDR 0-1 range

---
 DirectXTex/BC6HBC7.cpp | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/DirectXTex/BC6HBC7.cpp b/DirectXTex/BC6HBC7.cpp
index e813862..37ff900 100644
--- a/DirectXTex/BC6HBC7.cpp
+++ b/DirectXTex/BC6HBC7.cpp
@@ -1180,6 +1180,7 @@ namespace
 
 
     //-------------------------------------------------------------------------------------
+    template<bool ishdr>
     float OptimizeRGB(
         _In_reads_(NUM_PIXELS_PER_BLOCK) const HDRColorA* const pPoints,
         _Out_ HDRColorA* pX,
@@ -1193,8 +1194,17 @@ namespace
         const float *pD = (3 == cSteps) ? pD3 : pD4;
 
         // Find Min and Max points, as starting point
-        HDRColorA X(1.0f, 1.0f, 1.0f, 0.0f);
-        HDRColorA Y(0.0f, 0.0f, 0.0f, 0.0f);
+        HDRColorA X, Y;
+        if (ishdr)
+        {
+            X = HDRColorA{ FLT_MAX, FLT_MAX, FLT_MAX, 0.0f };
+            Y = HDRColorA{ -FLT_MAX, -FLT_MAX, -FLT_MAX, 0.0f };
+        }
+        else
+        {
+            X = HDRColorA{ 1.0f, 1.0f, 1.0f, 0.0f };
+            Y = HDRColorA{ 0.0f, 0.0f, 0.0f, 0.0f };
+        }
 
         for (size_t iPoint = 0; iPoint < cPixels; iPoint++)
         {
@@ -2492,7 +2502,7 @@ float D3DX_BC6H::RoughMSE(EncodeParams* pEP) const noexcept
         }
 
         HDRColorA epA, epB;
-        OptimizeRGB(pEP->aHDRPixels, &epA, &epB, 4, np, auPixIdx);
+        OptimizeRGB<true>(pEP->aHDRPixels, &epA, &epB, 4, np, auPixIdx);
         aEndPts[p].A.Set(epA, pEP->bSigned);
         aEndPts[p].B.Set(epB, pEP->bSigned);
         if (pEP->bSigned)
@@ -3464,7 +3474,7 @@ float D3DX_BC7::RoughMSE(EncodeParams* pEP, size_t uShape, size_t uIndexMode) no
             }
 
             HDRColorA epA, epB;
-            OptimizeRGB(pEP->aHDRPixels, &epA, &epB, 4, np, auPixIdx);
+            OptimizeRGB<false>(pEP->aHDRPixels, &epA, &epB, 4, np, auPixIdx);
             epA.Clamp(0.0f, 1.0f);
             epB.Clamp(0.0f, 1.0f);
             epA *= 255.0f;