81 lines
3.7 KiB
C#
81 lines
3.7 KiB
C#
using System.Buffers.Binary;
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namespace Age.Engine.Sys4;
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/// <summary>A decoded Windows cursor image and its native hotspot.</summary>
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public sealed record CursorImage(RgbaImage Image, int HotspotX, int HotspotY);
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/// <summary>Decoder for Himegari's monochrome Windows .CUR resources.</summary>
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public static class CurDecoder
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{
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public static CursorImage Decode(ReadOnlySpan<byte> file, string name = "CUR")
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{
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if (file.Length < 22 || U16(file, 0) != 0 || U16(file, 2) != 2 || U16(file, 4) < 1)
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throw new InvalidDataException($"{name}: expected a Windows cursor directory");
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int width = file[6] == 0 ? 256 : file[6];
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int height = file[7] == 0 ? 256 : file[7];
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int hotspotX = U16(file, 10);
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int hotspotY = U16(file, 12);
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int imageSize = I32(file, 14);
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int imageOffset = I32(file, 18);
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if (imageSize <= 0 || imageOffset < 22 || imageOffset > file.Length - imageSize)
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throw new InvalidDataException($"{name}: cursor image range is invalid");
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int headerSize = I32(file, imageOffset);
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if (headerSize < 40 || imageOffset > file.Length - headerSize)
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throw new InvalidDataException($"{name}: unsupported bitmap header");
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int dibWidth = I32(file, imageOffset + 4);
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int dibHeight = I32(file, imageOffset + 8);
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int planes = U16(file, imageOffset + 12);
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int bitsPerPixel = U16(file, imageOffset + 14);
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int compression = I32(file, imageOffset + 16);
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if (dibWidth != width || System.Math.Abs(dibHeight) != height * 2 || planes != 1
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|| bitsPerPixel != 1 || compression != 0)
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throw new InvalidDataException($"{name}: expected an uncompressed 1-bit {width}x{height} cursor");
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int paletteOffset = checked(imageOffset + headerSize);
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if (paletteOffset > file.Length - 8) throw new InvalidDataException($"{name}: palette is truncated");
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int xorStride = checked(((width + 31) / 32) * 4);
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int maskBytes = checked(xorStride * height);
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int xorOffset = checked(paletteOffset + 8);
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int andOffset = checked(xorOffset + maskBytes);
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if (andOffset > file.Length - maskBytes) throw new InvalidDataException($"{name}: cursor masks are truncated");
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var rgba = new byte[checked(width * height * 4)];
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bool bottomUp = dibHeight > 0;
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for (int y = 0; y < height; y++)
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{
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int sourceY = bottomUp ? height - 1 - y : y;
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int xorRow = xorOffset + sourceY * xorStride;
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int andRow = andOffset + sourceY * xorStride;
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for (int x = 0; x < width; x++)
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{
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int shift = 7 - (x & 7);
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int paletteIndex = (file[xorRow + (x >> 3)] >> shift) & 1;
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bool transparent = ((file[andRow + (x >> 3)] >> shift) & 1) != 0 && paletteIndex == 0;
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int palette = paletteOffset + paletteIndex * 4;
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int dst = (y * width + x) * 4;
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rgba[dst] = file[palette + 2];
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rgba[dst + 1] = file[palette + 1];
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rgba[dst + 2] = file[palette];
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rgba[dst + 3] = transparent ? (byte)0 : (byte)255;
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}
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}
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return new CursorImage(new RgbaImage(width, height, rgba), hotspotX, hotspotY);
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}
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private static int U16(ReadOnlySpan<byte> data, int offset)
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{
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if ((uint)offset > (uint)(data.Length - 2)) throw new InvalidDataException("CUR: truncated field");
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return BinaryPrimitives.ReadUInt16LittleEndian(data[offset..]);
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}
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private static int I32(ReadOnlySpan<byte> data, int offset)
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{
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if ((uint)offset > (uint)(data.Length - 4)) throw new InvalidDataException("CUR: truncated field");
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return BinaryPrimitives.ReadInt32LittleEndian(data[offset..]);
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}
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}
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