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Decode color drag-pan cursor

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This commit is contained in:
gamer147
2026-07-21 13:14:02 -04:00
parent 44bbf5b6b4
commit b0971f2047
5 changed files with 83 additions and 15 deletions
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41
engine/Age.Engine/Sys4/CurDecoder.cs
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@@ -5,7 +5,7 @@ namespace Age.Engine.Sys4;
/// <summary>A decoded Windows cursor image and its native hotspot.</summary>
public sealed record CursorImage(RgbaImage Image, int HotspotX, int HotspotY);
/// <summary>Decoder for Himegari's monochrome Windows .CUR resources.</summary>
/// <summary>Decoder for Himegari's paletted Windows .CUR resources.</summary>
public static class CurDecoder
{
public static CursorImage Decode(ReadOnlySpan<byte> file, string name = "CUR")
@@ -31,16 +31,28 @@ public static class CurDecoder
int bitsPerPixel = U16(file, imageOffset + 14);
int compression = I32(file, imageOffset + 16);
if (dibWidth != width || System.Math.Abs(dibHeight) != height * 2 || planes != 1
|| bitsPerPixel != 1 || compression != 0)
throw new InvalidDataException($"{name}: expected an uncompressed 1-bit {width}x{height} cursor");
|| bitsPerPixel is not (1 or 4) || compression != 0)
throw new InvalidDataException(
$"{name}: expected an uncompressed 1-bit or 4-bit {width}x{height} cursor");
int paletteOffset = checked(imageOffset + headerSize);
if (paletteOffset > file.Length - 8) throw new InvalidDataException($"{name}: palette is truncated");
int xorStride = checked(((width + 31) / 32) * 4);
int maskBytes = checked(xorStride * height);
int xorOffset = checked(paletteOffset + 8);
int andOffset = checked(xorOffset + maskBytes);
if (andOffset > file.Length - maskBytes) throw new InvalidDataException($"{name}: cursor masks are truncated");
int colorsUsed = I32(file, imageOffset + 32);
int maximumPaletteEntries = 1 << bitsPerPixel;
int paletteEntries = colorsUsed == 0 ? maximumPaletteEntries : colorsUsed;
if (paletteEntries <= 0 || paletteEntries > maximumPaletteEntries)
throw new InvalidDataException($"{name}: cursor palette size is invalid");
int paletteBytes = checked(paletteEntries * 4);
if (paletteOffset > file.Length - paletteBytes)
throw new InvalidDataException($"{name}: palette is truncated");
int xorStride = checked(((width * bitsPerPixel + 31) / 32) * 4);
int andStride = checked(((width + 31) / 32) * 4);
int xorBytes = checked(xorStride * height);
int andBytes = checked(andStride * height);
int xorOffset = checked(paletteOffset + paletteBytes);
int andOffset = checked(xorOffset + xorBytes);
if (andOffset > file.Length - andBytes)
throw new InvalidDataException($"{name}: cursor masks are truncated");
var rgba = new byte[checked(width * height * 4)];
bool bottomUp = dibHeight > 0;
@@ -48,12 +60,15 @@ public static class CurDecoder
{
int sourceY = bottomUp ? height - 1 - y : y;
int xorRow = xorOffset + sourceY * xorStride;
int andRow = andOffset + sourceY * xorStride;
int andRow = andOffset + sourceY * andStride;
for (int x = 0; x < width; x++)
{
int shift = 7 - (x & 7);
int paletteIndex = (file[xorRow + (x >> 3)] >> shift) & 1;
bool transparent = ((file[andRow + (x >> 3)] >> shift) & 1) != 0 && paletteIndex == 0;
int paletteIndex = bitsPerPixel == 1
? (file[xorRow + (x >> 3)] >> (7 - (x & 7))) & 1
: (file[xorRow + (x >> 1)] >> ((1 - (x & 1)) * 4)) & 0xf;
int maskShift = 7 - (x & 7);
bool transparent = ((file[andRow + (x >> 3)] >> maskShift) & 1) != 0
&& paletteIndex == 0;
int palette = paletteOffset + paletteIndex * 4;
int dst = (y * width + x) * 4;
rgba[dst] = file[palette + 2];