Reduce CLX header size from 10 to 6

We remain compatible with the 10-byte header size,
and actually now support any header size.

Source/engine/clx_sprite.hpp

@@ -5,21 +5,20 @@
  * @brief CLX format sprites.
  *
  * CLX is a format used for DevilutionX graphics at runtime.
+ * CLX encodes pixel in the same way CL2 but encodes metadata differently.
  *
- * It is identical to CL2, except we use the frame header to store the frame's width and height.
+ * Unlike CL2:
  *
- * CLX frame header (10 bytes, same as CL2):
+ * 1. CLX frame header stores frame width and height.
+ * 2. CLX frame header does not store 32-pixel block offsets.
  *
- *      Bytes |   Type   | Value
- *     :-----:|:--------:|------------------------------------
- *      0..2  | uint16_t | offset to data start (same as CL2)
- *      2..4  | uint16_t | width
- *      4..6  | uint16_t | height
- *      6..10 |    -     | unused
+ * CLX frame header is 6 bytes:
  *
- * The CLX format is otherwise identical to CL2.
- *
- * Since the header is identical to CL2, CL2 can be converted to CLX without reallocation.
+ *  Bytes |   Type   | Value
+ * :-----:|:--------:|-------------
+ *  0..2  | uint16_t | header size
+ *  2..4  | uint16_t | width
+ *  4..6  | uint16_t | height
  *
  * CL2 reference: https://github.com/savagesteel/d1-file-formats/blob/master/PC-Mac/CL2.md#2-file-structure
  */
@@ -42,12 +41,10 @@ class OptionalClxSprite;
  * @brief A single CLX sprite.
  */
 class ClxSprite {
-	static constexpr uint32_t HeaderSize = 10;
-
 public:
 	explicit constexpr ClxSprite(const uint8_t *data, uint32_t dataSize)
 	    : data_(data)
-	    , pixel_data_size_(dataSize - HeaderSize)
+	    , pixel_data_size_(dataSize - LoadLE16(data))
 	{
 		assert(data != nullptr);
 	}
@@ -69,7 +66,7 @@ public:
 	 */
 	[[nodiscard]] constexpr const uint8_t *pixelData() const
 	{
-		return &data_[HeaderSize];
+		return &data_[LoadLE16(data_)];
 	}
 
 	[[nodiscard]] constexpr uint32_t pixelDataSize() const

Source/utils/cel_to_clx.cpp

@@ -86,9 +86,8 @@ OwnedClxSpriteListOrSheet CelToClx(const uint8_t *data, size_t size, PointerOrVa
 
 			// CLX frame header.
 			const size_t frameHeaderPos = cl2Data.size();
-			constexpr size_t FrameHeaderSize = 10;
-			cl2Data.resize(cl2Data.size() + FrameHeaderSize);
-			WriteLE16(&cl2Data[frameHeaderPos], FrameHeaderSize);
+			cl2Data.resize(cl2Data.size() + ClxFrameHeaderSize);
+			WriteLE16(&cl2Data[frameHeaderPos], ClxFrameHeaderSize);
 			WriteLE16(&cl2Data[frameHeaderPos + 2], frameWidth);
 
 			unsigned transparentRunWidth = 0;
@@ -111,7 +110,6 @@ OwnedClxSpriteListOrSheet CelToClx(const uint8_t *data, size_t size, PointerOrVa
 				++frameHeight;
 			}
 			WriteLE16(&cl2Data[frameHeaderPos + 4], static_cast<uint16_t>(frameHeight));
-			memset(&cl2Data[frameHeaderPos + 6], 0, 4);
 			AppendClxTransparentRun(transparentRunWidth, cl2Data);
 		}
 

Source/utils/cl2_to_clx.cpp

@@ -56,9 +56,8 @@ uint16_t Cl2ToClx(const uint8_t *data, size_t size,
 			const uint16_t frameWidth = widthOrWidths.HoldsPointer() ? widthOrWidths.AsPointer()[frame - 1] : widthOrWidths.AsValue();
 
 			const size_t frameHeaderPos = clxData.size();
-			constexpr size_t FrameHeaderSize = 10;
-			clxData.resize(clxData.size() + FrameHeaderSize);
-			WriteLE16(&clxData[frameHeaderPos], FrameHeaderSize);
+			clxData.resize(clxData.size() + ClxFrameHeaderSize);
+			WriteLE16(&clxData[frameHeaderPos], ClxFrameHeaderSize);
 			WriteLE16(&clxData[frameHeaderPos + 2], frameWidth);
 
 			unsigned transparentRunWidth = 0;
@@ -104,7 +103,6 @@ uint16_t Cl2ToClx(const uint8_t *data, size_t size,
 			AppendClxTransparentRun(transparentRunWidth, clxData);
 
 			WriteLE16(&clxData[frameHeaderPos + 4], static_cast<uint16_t>(frameHeight));
-			memset(&clxData[frameHeaderPos + 6], 0, 4);
 		}
 
 		WriteLE32(&clxData[clxDataOffset + 4 * (1 + static_cast<size_t>(numFrames))], static_cast<uint32_t>(clxData.size() - clxDataOffset));

Source/utils/clx_encode.hpp

@@ -6,6 +6,17 @@
 
 namespace devilution {
 
+/**
+ * CLX frame header is 6 bytes:
+ *
+ *  Bytes |   Type   | Value
+ * :-----:|:--------:|-------------
+ *  0..2  | uint16_t | header size
+ *  2..4  | uint16_t | width
+ *  4..6  | uint16_t | height
+ */
+constexpr size_t ClxFrameHeaderSize = 6;
+
 inline void AppendClxTransparentRun(unsigned width, std::vector<uint8_t> &out)
 {
 	while (width >= 0x7F) {

Source/utils/pcx_to_clx.cpp

@@ -98,20 +98,13 @@ OptionalOwnedClxSpriteList PcxToClx(AssetHandle &handle, size_t fileSize, int nu
 	for (unsigned frame = 1; frame <= numFrames; ++frame) {
 		WriteLE32(&cl2Data[4 * static_cast<size_t>(frame)], static_cast<uint32_t>(cl2Data.size()));
 
-		// Frame header: 5 16-bit values:
-		// 1. Offset to start of the pixel data.
-		// 2. Width
-		// 3. Height
-		// 4..5. Unused (0)
 		const size_t frameHeaderPos = cl2Data.size();
-		constexpr size_t FrameHeaderSize = 10;
-		cl2Data.resize(cl2Data.size() + FrameHeaderSize);
+		cl2Data.resize(cl2Data.size() + ClxFrameHeaderSize);
 
 		// Frame header:
-		WriteLE16(&cl2Data[frameHeaderPos], FrameHeaderSize);
+		WriteLE16(&cl2Data[frameHeaderPos], ClxFrameHeaderSize);
 		WriteLE16(&cl2Data[frameHeaderPos + 2], static_cast<uint16_t>(width));
 		WriteLE16(&cl2Data[frameHeaderPos + 4], static_cast<uint16_t>(frameHeight));
-		memset(&cl2Data[frameHeaderPos + 6], 0, 4);
 
 		for (unsigned j = 0; j < frameHeight; ++j) {
 			uint8_t *buffer = &frameBuffer[static_cast<size_t>(j) * width];

Source/utils/surface_to_clx.cpp

@@ -31,17 +31,11 @@ OwnedClxSpriteList SurfaceToClx(const Surface &surface, unsigned numFrames,
 	for (unsigned frame = 1; frame <= numFrames; ++frame) {
 		WriteLE32(&clxData[4 * static_cast<size_t>(frame)], static_cast<uint32_t>(clxData.size()));
 
-		// Frame header: 5 16-bit values:
-		// 1. Offset to start of the pixel data.
-		// 2. Width
-		// 3. Height
-		// 4..5. Unused (0)
 		const size_t frameHeaderPos = clxData.size();
-		constexpr size_t FrameHeaderSize = 10;
-		clxData.resize(clxData.size() + FrameHeaderSize);
+		clxData.resize(clxData.size() + ClxFrameHeaderSize);
 
 		// Frame header:
-		WriteLE16(&clxData[frameHeaderPos], FrameHeaderSize);
+		WriteLE16(&clxData[frameHeaderPos], ClxFrameHeaderSize);
 		WriteLE16(&clxData[frameHeaderPos + 2], static_cast<uint16_t>(width));
 		WriteLE16(&clxData[frameHeaderPos + 4], static_cast<uint16_t>(frameHeight));
 		memset(&clxData[frameHeaderPos + 6], 0, 4);