From f5e0aa4f9fb77216ebe326f3371e49831c6bb089 Mon Sep 17 00:00:00 2001
From: Pavel Krajcevski <pavel@cs.unc.edu>
Date: Tue, 10 Sep 2013 13:21:48 -0400
Subject: [PATCH] Make sure to clear the MSBs of channels that have zero depth
 that get converted to higher depth values

---
 PVRTCEncoder/src/Pixel.cpp      |  4 +++-
 PVRTCEncoder/test/PixelTest.cpp | 13 +++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/PVRTCEncoder/src/Pixel.cpp b/PVRTCEncoder/src/Pixel.cpp
index d8504a3..d64b9c1 100644
--- a/PVRTCEncoder/src/Pixel.cpp
+++ b/PVRTCEncoder/src/Pixel.cpp
@@ -112,9 +112,11 @@ namespace PVRTCC {
     assert(newDepth <= 8);
     assert(oldDepth <= 8);
 
-    if(oldDepth == newDepth || oldDepth == 0) {
+    if(oldDepth == newDepth) {
       // Do nothing
       return val;
+    } else if(oldDepth == 0 && newDepth != 0) {
+      return (1 << newDepth) - 1;
     } else if(newDepth > oldDepth) {
       uint8 bitsLeft = newDepth;
       uint8 ret = 0;
diff --git a/PVRTCEncoder/test/PixelTest.cpp b/PVRTCEncoder/test/PixelTest.cpp
index d1d24f2..afc380f 100644
--- a/PVRTCEncoder/test/PixelTest.cpp
+++ b/PVRTCEncoder/test/PixelTest.cpp
@@ -153,6 +153,19 @@ TEST(Pixel, ChangeChannelBitDepth) {
   EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 0), 0xFF);
 }
 
+TEST(Pixel, ChangeChannelBitDepthFromZero) {
+  uint8 val = 0x43;
+  uint8 depth = 0;
+
+  EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 8), 0xFF);
+  EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 7), 0x7F);
+  EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 6), 0x3F);
+  EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 2), 0x03);
+
+  // Shouldn't change it...
+  EXPECT_EQ(PVRTCC::Pixel::ChangeBitDepth(val, depth, 0), 0x43);
+}
+
 TEST(Pixel, ChangePixelBitDepth) {
   const uint8 bits[4] = { 0x86, 0xC0, 0x0, 0x0 };
   const uint8 depth[4] = {7, 3, 0, 0};