Add pixel packing routines

PVRTCEncoder/src/Pixel.cpp

@@ -108,6 +108,44 @@ namespace PVRTCC {
     }
   }
 
+  void Pixel::ToBits(uint8 *bits, uint32 numBytes, uint32 bitOffset) const {
+#ifndef NDEBUG
+    uint32 bitDepthSum = bitOffset;
+    for(int i = 0; i < 4; i++) {
+      bitDepthSum += m_BitDepth[i];
+    }
+    assert((bitDepthSum / 8) < numBytes);
+#endif
+
+    uint8 byteIdx = 0;
+    while(bitOffset > 8) {
+      byteIdx++;
+      bitOffset -= 8;
+    }
+
+    uint8 bitIdx = bitOffset;
+    for(int i = 3; i >= 0; i--) {
+      uint8 val = Component(i);
+      uint8 depth = m_BitDepth[i];
+
+      if(depth + bitIdx > 8) {
+        uint8 nextBitIdx = depth - (8 - bitIdx);
+        uint16 v = static_cast<uint16>(val);
+        bits[byteIdx++] |= (v << bitIdx) & 0xFF;
+        bitIdx = nextBitIdx;
+        bits[byteIdx] = (v >> (depth - bitIdx)) & 0xFF;
+      } else {
+        bits[byteIdx] |= (val << bitIdx) & 0xFF;
+        bitIdx += depth;
+      }
+
+      if(bitIdx == 8) {
+        bitIdx = 0;
+        byteIdx++;
+      }
+    }
+  }
+
   uint8 Pixel::ChangeBitDepth(uint8 val, uint8 oldDepth, uint8 newDepth) {
     assert(newDepth <= 8);
     assert(oldDepth <= 8);

PVRTCEncoder/src/Pixel.h

@@ -82,6 +82,13 @@ class Pixel {
                 const uint8 channelDepth[4] = static_cast<uint8 *>(0),
                 uint8 bitOffset = 0);
 
+  // This function is the converse of FromBits. It will pack a pixel
+  // into a specified buffer based on the bit depth of the pixel. The
+  // bitOffset determines at which bit to start from. The bits are written
+  // starting from the LSB of bits[0]. numBytes is a sanity check and isn't
+  // used in release mode.
+  void ToBits(uint8 *bits, uint32 numBytes, uint32 bitOffset = 0) const;
+
   // Changes the depth of each pixel. This scales the values to
   // the appropriate bit depth by either truncating the least
   // significant bits when going from larger to smaller bit depth

PVRTCEncoder/test/PixelTest.cpp

@@ -133,6 +133,32 @@ TEST(Pixel, FromBitsAndAssociatedConstructor) {
   }
 }
 
+TEST(Pixel, ToBits) {
+  PVRTCC::Pixel p;
+
+  uint8 bitDepth[4] = { 2, 8, 1, 7 };
+  p.ChangeBitDepth(bitDepth);
+
+  p.A() = 0x2;
+  p.R() = 0x56;
+  p.G() = 0;
+  p.B() = 0x4F;
+
+  uint8 bits[3];
+  memset(bits, 0, sizeof(bits));
+  p.ToBits(bits, sizeof(bits));
+
+  EXPECT_EQ(bits[0], 0x4F);
+  EXPECT_EQ(bits[1], 0x56);
+  EXPECT_EQ(bits[2], 0x2);
+
+  memset(bits, 0, sizeof(bits));
+  p.ToBits(bits, 3, 2);
+  EXPECT_EQ(bits[0], 0x3C);
+  EXPECT_EQ(bits[1], 0x59);
+  EXPECT_EQ(bits[2], 0x09);
+}
+
 TEST(Pixel, ChangeChannelBitDepth) {
   uint8 val = 0x43;
   uint8 depth = 7;