GPU: Add fallback when 16-bit formats are not supported (#4108)

* Add conversion for 16 bit RGBA formats (not supported in Rosetta)

* Rebase fix

Rebase fix

* Forgot to remove this

* Fix RGBA16 format conversion

* Add RGBA4 -> RGBA8 conversion

* Handle host stride alignment

* Address Feedback Part 1

* Can't count

* Don't zero out rgb when alpha is 0

* Separate RGBA4 and 5-bit component formats

Not sure of a better way to name them...

* Add A1B5G5R5 conversion

* Put this in the right place.

* Make format naming consistent for capabilities

* Change method names

2 files changed, 189 insertions, 12 deletions

diff --git a/Ryujinx.Graphics.Texture/LayoutConverter.cs b/Ryujinx.Graphics.Texture/LayoutConverter.cs
index 188ae0c1..b8ec9748 100644
--- a/Ryujinx.Graphics.Texture/LayoutConverter.cs
+++ b/Ryujinx.Graphics.Texture/LayoutConverter.cs
@@ -7,7 +7,7 @@ namespace Ryujinx.Graphics.Texture
 {
     public static class LayoutConverter
     {
-        private const int HostStrideAlignment = 4;
+        public const int HostStrideAlignment = 4;
 
         public static void ConvertBlockLinearToLinear(
             Span<byte> dst,
diff --git a/Ryujinx.Graphics.Texture/PixelConverter.cs b/Ryujinx.Graphics.Texture/PixelConverter.cs
index d7e45a69..add25cd3 100644
--- a/Ryujinx.Graphics.Texture/PixelConverter.cs
+++ b/Ryujinx.Graphics.Texture/PixelConverter.cs
@@ -1,3 +1,4 @@
+using Ryujinx.Common;
 using System;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
@@ -7,30 +8,206 @@ namespace Ryujinx.Graphics.Texture
 {
     public static class PixelConverter
     {
-        public unsafe static byte[] ConvertR4G4ToR4G4B4A4(ReadOnlySpan<byte> data)
+        private static (int remainder, int outRemainder, int height) GetLineRemainders(int length, int width, int bpp, int outBpp)
+        {
+            int stride = BitUtils.AlignUp(width * bpp, LayoutConverter.HostStrideAlignment);
+            int remainder = stride / bpp - width;
+
+            int outStride = BitUtils.AlignUp(width * outBpp, LayoutConverter.HostStrideAlignment);
+            int outRemainder = outStride / outBpp - width;
+
+            return (remainder, outRemainder, length / stride);
+        }
+
+        public unsafe static byte[] ConvertR4G4ToR4G4B4A4(ReadOnlySpan<byte> data, int width)
         {
             byte[] output = new byte[data.Length * 2];
-            int start = 0;
 
-            if (Sse41.IsSupported)
+            (int remainder, int outRemainder, int height) = GetLineRemainders(data.Length, width, 1, 2);
+
+            Span<ushort> outputSpan = MemoryMarshal.Cast<byte, ushort>(output);
+
+            if (remainder == 0)
+            {
+                int start = 0;
+
+                if (Sse41.IsSupported)
+                {
+                    int sizeTrunc = data.Length & ~7;
+                    start = sizeTrunc;
+
+                    fixed (byte* inputPtr = data, outputPtr = output)
+                    {
+                        for (ulong offset = 0; offset < (ulong)sizeTrunc; offset += 8)
+                        {
+                            Sse2.Store(outputPtr + offset * 2, Sse41.ConvertToVector128Int16(inputPtr + offset).AsByte());
+                        }
+                    }
+                }
+
+                for (int i = start; i < data.Length; i++)
+                {
+                    outputSpan[i] = (ushort)data[i];
+                }
+            }
+            else
             {
-                int sizeTrunc = data.Length & ~7;
-                start = sizeTrunc;
+                int offset = 0;
+                int outOffset = 0;
 
-                fixed (byte* inputPtr = data, outputPtr = output)
+                for (int y = 0; y < height; y++)
                 {
-                    for (ulong offset = 0; offset < (ulong)sizeTrunc; offset += 8)
+                    for (int x = 0; x < width; x++)
                     {
-                        Sse2.Store(outputPtr + offset * 2, Sse41.ConvertToVector128Int16(inputPtr + offset).AsByte());
+                        outputSpan[outOffset++] = data[offset++];
                     }
+
+                    offset += remainder;
+                    outOffset += outRemainder;
                 }
             }
 
-            Span<ushort> outputSpan = MemoryMarshal.Cast<byte, ushort>(output);
+            return output;
+        }
+
+        public unsafe static byte[] ConvertR5G6B5ToR8G8B8A8(ReadOnlySpan<byte> data, int width)
+        {
+            byte[] output = new byte[data.Length * 2];
+            int offset = 0;
+            int outOffset = 0;
+
+            (int remainder, int outRemainder, int height) = GetLineRemainders(data.Length, width, 2, 4);
+
+            ReadOnlySpan<ushort> inputSpan = MemoryMarshal.Cast<byte, ushort>(data);
+            Span<uint> outputSpan = MemoryMarshal.Cast<byte, uint>(output);
 
-            for (int i = start; i < data.Length; i++)
+            for (int y = 0; y < height; y++)
             {
-                outputSpan[i] = (ushort)data[i];
+                for (int x = 0; x < width; x++)
+                {
+                    uint packed = inputSpan[offset++];
+
+                    uint outputPacked =  0xff000000;
+                         outputPacked |= (packed << 3) & 0x000000f8;
+                         outputPacked |= (packed << 8) & 0x00f80000;
+
+                    // Replicate 5 bit components.
+                    outputPacked |= (outputPacked >> 5) & 0x00070007;
+
+                    // Include and replicate 6 bit component.
+                    outputPacked |= ((packed << 5) & 0x0000fc00) | ((packed >> 1) & 0x00000300);
+
+                    outputSpan[outOffset++] = outputPacked;
+                }
+
+                offset += remainder;
+                outOffset += outRemainder;
+            }
+
+            return output;
+        }
+
+        public unsafe static byte[] ConvertR5G5B5ToR8G8B8A8(ReadOnlySpan<byte> data, int width, bool forceAlpha)
+        {
+            byte[] output = new byte[data.Length * 2];
+            int offset = 0;
+            int outOffset = 0;
+
+            (int remainder, int outRemainder, int height) = GetLineRemainders(data.Length, width, 2, 4);
+
+            ReadOnlySpan<ushort> inputSpan = MemoryMarshal.Cast<byte, ushort>(data);
+            Span<uint> outputSpan = MemoryMarshal.Cast<byte, uint>(output);
+
+            for (int y = 0; y < height; y++)
+            {
+                for (int x = 0; x < width; x++)
+                {
+                    uint packed = inputSpan[offset++];
+
+                    uint a = forceAlpha ? 1 : (packed >> 15);
+
+                    uint outputPacked =  a * 0xff000000;
+                         outputPacked |= (packed << 3) & 0x000000f8;
+                         outputPacked |= (packed << 6) & 0x0000f800;
+                         outputPacked |= (packed << 9) & 0x00f80000;
+
+                    // Replicate 5 bit components.
+                    outputPacked |= (outputPacked >> 5) & 0x00070707;
+
+                    outputSpan[outOffset++] = outputPacked;
+                }
+
+                offset += remainder;
+                outOffset += outRemainder;
+            }
+
+            return output;
+        }
+
+        public unsafe static byte[] ConvertA1B5G5R5ToR8G8B8A8(ReadOnlySpan<byte> data, int width)
+        {
+            byte[] output = new byte[data.Length * 2];
+            int offset = 0;
+            int outOffset = 0;
+
+            (int remainder, int outRemainder, int height) = GetLineRemainders(data.Length, width, 2, 4);
+
+            ReadOnlySpan<ushort> inputSpan = MemoryMarshal.Cast<byte, ushort>(data);
+            Span<uint> outputSpan = MemoryMarshal.Cast<byte, uint>(output);
+
+            for (int y = 0; y < height; y++)
+            {
+                for (int x = 0; x < width; x++)
+                {
+                    uint packed = inputSpan[offset++];
+
+                    uint a = packed >> 15;
+
+                    uint outputPacked = a * 0xff000000;
+                    outputPacked |= (packed >> 8) & 0x000000f8;
+                    outputPacked |= (packed << 5) & 0x0000f800;
+                    outputPacked |= (packed << 18) & 0x00f80000;
+
+                    // Replicate 5 bit components.
+                    outputPacked |= (outputPacked >> 5) & 0x00070707;
+
+                    outputSpan[outOffset++] = outputPacked;
+                }
+
+                offset += remainder;
+                outOffset += outRemainder;
+            }
+
+            return output;
+        }
+
+        public unsafe static byte[] ConvertR4G4B4A4ToR8G8B8A8(ReadOnlySpan<byte> data, int width)
+        {
+            byte[] output = new byte[data.Length * 2];
+            int offset = 0;
+            int outOffset = 0;
+
+            (int remainder, int outRemainder, int height) = GetLineRemainders(data.Length, width, 2, 4);
+
+            ReadOnlySpan<ushort> inputSpan = MemoryMarshal.Cast<byte, ushort>(data);
+            Span<uint> outputSpan = MemoryMarshal.Cast<byte, uint>(output);
+
+            for (int y = 0; y < height; y++)
+            {
+                for (int x = 0; x < width; x++)
+                {
+                    uint packed = inputSpan[offset++];
+
+                    uint outputPacked =  packed         & 0x0000000f;
+                         outputPacked |= (packed << 4)  & 0x00000f00;
+                         outputPacked |= (packed << 8)  & 0x000f0000;
+                         outputPacked |= (packed << 12) & 0x0f000000;
+
+                    outputSpan[outOffset++] = outputPacked * 0x11;
+                }
+
+                offset += remainder;
+                outOffset += outRemainder;
             }
 
             return output;