fix(agc): rect-list/NGG strips, Index8 expand, and GE_INDX_OFFSET

NGG single-rect UI needs triangle-strip expansion; Prospero Index8 must expand to host u16; glyphs need base vertex from GE_INDX_OFFSET. Skip param-less rect-lists instead of inventing colour draws. Co-authored-by: Cursor <cursoragent@cursor.com>
2026-07-28 05:30:57 +08:00 · 2026-07-23 01:46:52 +01:00
parent 83745325c3
commit 4b9d2cafac
9 changed files with 606 additions and 94 deletions
@@ -104,6 +104,10 @@ public static partial class AgcExports
    private const uint ComputeNumThreadZ = 0x209;
    private const uint SpiPsInputCntl0 = 0x191;
    private const uint VgtPrimitiveType = 0x242;
+    private const uint VgtIndexType = 0x243;
+    // GE_INDX_OFFSET — base vertex for DrawIndexed / firstVertex for
+    // DrawIndexAuto. Glyph meshes and UI icon batches rely on this.
+    private const uint GeIndxOffset = 0x24A;
    private const uint PaScScreenScissorTl = 0x0C;
    private const uint PaScScreenScissorBr = 0x0D;
    private const uint CbTargetMask = 0x8E;
@@ -453,6 +457,7 @@ public static partial class AgcExports
        uint AttributeCount,
        uint VertexCount,
        uint InstanceCount,
+        int BaseVertex,
        GuestIndexBuffer? IndexBuffer,
        IReadOnlyList<TranslatedImageBinding> Textures,
        IReadOnlyList<Gen5GlobalMemoryBinding> GlobalMemoryBindings,
@@ -3705,7 +3710,8 @@ public static partial class AgcExports
                        vertexBuffers,
                        pendingComposite.RenderState,
                        pendingComposite.DepthTarget,
-                        pendingComposite.PixelShaderAddress);
+                        pendingComposite.PixelShaderAddress,
+                        pendingComposite.BaseVertex);
                    TraceAgcShader(
                        $"agc.deferred_composite ps=0x{pendingComposite.PixelShaderAddress:X16} " +
                        $"src=0x{pendingComposite.Textures.FirstOrDefault()?.Descriptor.Address ?? 0:X16} " +
@@ -5728,6 +5734,10 @@ public static partial class AgcExports
                }

                directDestination[startRegister + index] = value;
+                if (op == ItSetUconfigReg)
+                {
+                    ApplyUcIndexTypeIfNeeded(state, startRegister + index, value);
+                }
            }

            return;
@@ -5762,6 +5772,25 @@ public static partial class AgcExports
            // Dropping it leaves stale depth/render-control state active in
            // later passes.
            destination[registerOffset] = value;
+            if (register == RUcRegsIndirect)
+            {
+                ApplyUcIndexTypeIfNeeded(state, registerOffset, value);
+            }
+        }
+    }
+
+    /// <summary>
+    /// GraphicsDcbSetIndexSize writes VGT_INDEX_TYPE via SET_UCONFIG_REG.
+    /// Mirror that into <see cref="SubmittedDcbState.IndexSize"/>.
+    /// </summary>
+    private static void ApplyUcIndexTypeIfNeeded(
+        SubmittedDcbState state,
+        uint registerOffset,
+        uint value)
+    {
+        if (registerOffset == VgtIndexType)
+        {
+            state.IndexSize = value & 0x3;
        }
    }

@@ -5958,7 +5987,8 @@ public static partial class AgcExports
                depthOnlyDraw.IndexBuffer,
                vertexBuffers,
                renderState,
-                depthOnlyDraw.PixelShaderAddress);
+                depthOnlyDraw.PixelShaderAddress,
+                depthOnlyDraw.BaseVertex);

            if (_traceAgcShader)
            {
@@ -6115,7 +6145,8 @@ public static partial class AgcExports
                        sharedVertexBuffers,
                        translatedDraw.RenderState,
                        translatedDraw.DepthTarget,
-                        translatedDraw.PixelShaderAddress);
+                        translatedDraw.PixelShaderAddress,
+                        translatedDraw.BaseVertex);
                }
            }
            else
@@ -6157,7 +6188,8 @@ public static partial class AgcExports
                        translatedDraw.IndexBuffer,
                        vertexBuffers,
                        renderState,
-                        translatedDraw.PixelShaderAddress);
+                        translatedDraw.PixelShaderAddress,
+                        translatedDraw.BaseVertex);
                }
                else
                {
@@ -6460,6 +6492,7 @@ public static partial class AgcExports
            AttributeCount: 0,
            vertexCount,
            state.InstanceCount,
+            GetBaseVertex(state),
            indexed ? CreateGuestIndexBuffer(ctx, state, vertexCount) : null,
            textures,
            exportEvaluation.GlobalMemoryBindings,
@@ -6676,6 +6709,22 @@ public static partial class AgcExports
            }
        }

+        state.UcRegisters.TryGetValue(VgtPrimitiveType, out var earlyPrimitiveType);
+        if (IsRectListPrimitive(earlyPrimitiveType) &&
+            (exportEvaluation.VertexInputs is null || exportEvaluation.VertexInputs.Count == 0) &&
+            !VertexProgramExportsParameters(exportState.Program) &&
+            GetInterpolatedAttributeCount(pixelState) != 0)
+        {
+            ReturnPooledEvaluationArrays(exportEvaluation);
+            ReturnPooledEvaluationArrays(pixelEvaluation);
+            error =
+                $"rect-list-no-param-exports ps_inputs={GetInterpolatedAttributeCount(pixelState)}";
+            TraceAgcShader(
+                $"agc.rect_list_skip es=0x{exportShaderAddress:X16} " +
+                $"ps=0x{pixelShaderAddress:X16} {error}");
+            return false;
+        }
+
        // Every bound color target the shader exports to. Deferred renderers
        // draw a multi-render-target G-buffer (up to eight slots) in one pass.
        // Fall back to slot 0 if we cannot match any export to a bound target.
@@ -6965,6 +7014,7 @@ public static partial class AgcExports
            GetInterpolatedAttributeCount(pixelState),
            vertexCount,
            state.InstanceCount,
+            GetBaseVertex(state),
            indexed ? CreateGuestIndexBuffer(ctx, state, vertexCount) : null,
            textures,
            globalMemoryBindings,
@@ -7276,6 +7326,22 @@ public static partial class AgcExports
            ColorFunc: 0,
        };

+    private static AgcIndexHelpers.ProsperoIndexType GetProsperoIndexType(SubmittedDcbState state) =>
+        // IndexSize is latched from ItIndexType and from UC VGT_INDEX_TYPE
+        // writes. Do not fall back to a stale UC value when IndexSize is 0 —
+        // that mis-classified 16-bit draws as index8 and blanked meshes.
+        AgcIndexHelpers.Decode(state.IndexSize);
+
+    /// <summary>
+    /// ResolveVertexOffset for the common UC path: GE_INDX_OFFSET is the
+    /// DrawIndexed vertexOffset / DrawAuto firstVertex. Embedded-fetch SGPR
+    /// fallback is not required when the game latches this register (GTA UI).
+    /// </summary>
+    private static int GetBaseVertex(SubmittedDcbState state) =>
+        state.UcRegisters.TryGetValue(GeIndxOffset, out var indexOffset)
+            ? unchecked((int)indexOffset)
+            : 0;
+
    private static GuestIndexBuffer? CreateGuestIndexBuffer(
        CpuContext ctx,
        SubmittedDcbState state,
@@ -7286,17 +7352,40 @@ public static partial class AgcExports
            return null;
        }

-        var is32Bit = state.IndexSize != 0;
-        var bytesPerIndex = is32Bit ? sizeof(uint) : sizeof(ushort);
-        var byteOffset = checked((ulong)state.DrawIndexOffset * (uint)bytesPerIndex);
-        var byteCount = checked((int)(indexCount * (uint)bytesPerIndex));
-        var data = GuestDataPool.Shared.Rent(byteCount);
-        var span = data.AsSpan(0, byteCount);
+        var indexType = GetProsperoIndexType(state);
+        var guestBytesPerIndex = AgcIndexHelpers.GetGuestStrideBytes(indexType);
+        var byteOffset = checked((ulong)state.DrawIndexOffset * (uint)guestBytesPerIndex);
+        var guestByteCount = checked((int)(indexCount * (uint)guestBytesPerIndex));
        var address = state.IndexBufferAddress + byteOffset;
+
+        // Host backends only bind u16/u32. Expand kIndex8 -> u16.
+        if (indexType == AgcIndexHelpers.ProsperoIndexType.Index8)
+        {
+            var guestData = GuestDataPool.Shared.Rent(guestByteCount);
+            var guestSpan = guestData.AsSpan(0, guestByteCount);
+            if (!ctx.Memory.TryRead(address, guestSpan) &&
+                !KernelMemoryCompatExports.TryReadTrackedLibcHeap(address, guestSpan))
+            {
+                GuestDataPool.Shared.Return(guestData);
+                return null;
+            }
+
+            var hostByteCount = checked((int)(indexCount * sizeof(ushort)));
+            var hostData = GuestDataPool.Shared.Rent(hostByteCount);
+            AgcIndexHelpers.ExpandIndex8ToU16(
+                guestSpan,
+                hostData.AsSpan(0, hostByteCount));
+            GuestDataPool.Shared.Return(guestData);
+            return new GuestIndexBuffer(hostData, hostByteCount, Is32Bit: false, Pooled: true);
+        }
+
+        var is32Bit = indexType == AgcIndexHelpers.ProsperoIndexType.Index32;
+        var data = GuestDataPool.Shared.Rent(guestByteCount);
+        var span = data.AsSpan(0, guestByteCount);
        if (ctx.Memory.TryRead(address, span) ||
            KernelMemoryCompatExports.TryReadTrackedLibcHeap(address, span))
        {
-            return new GuestIndexBuffer(data, byteCount, is32Bit, Pooled: true);
+            return new GuestIndexBuffer(data, guestByteCount, is32Bit, Pooled: true);
        }

        GuestDataPool.Shared.Return(data);
@@ -7310,7 +7399,10 @@ public static partial class AgcExports
        bool indexed,
        out uint recordCount)
    {
-        recordCount = Math.Max(drawCount, Math.Max(state.InstanceCount, 1u));
+        var baseVertex = (uint)Math.Max(GetBaseVertex(state), 0);
+        recordCount = Math.Max(
+            baseVertex + drawCount,
+            Math.Max(state.InstanceCount, 1u));
        if (!indexed)
        {
            return true;
@@ -7321,8 +7413,8 @@ public static partial class AgcExports
            return false;
        }

-        var is32Bit = state.IndexSize != 0;
-        var bytesPerIndex = is32Bit ? sizeof(uint) : sizeof(ushort);
+        var indexType = GetProsperoIndexType(state);
+        var bytesPerIndex = AgcIndexHelpers.GetGuestStrideBytes(indexType);
        var byteOffset = checked((ulong)state.DrawIndexOffset * (uint)bytesPerIndex);
        var address = state.IndexBufferAddress + byteOffset;
        const int chunkBytes = 64 * 1024;
@@ -7347,12 +7439,22 @@ public static partial class AgcExports

                for (var index = 0; index < chunkIndices; index++)
                {
-                    var value = is32Bit
-                        ? BinaryPrimitives.ReadUInt32LittleEndian(
-                            span.Slice(index * sizeof(uint), sizeof(uint)))
-                        : BinaryPrimitives.ReadUInt16LittleEndian(
-                            span.Slice(index * sizeof(ushort), sizeof(ushort)));
-                    if (value == (is32Bit ? uint.MaxValue : ushort.MaxValue))
+                    uint value = indexType switch
+                    {
+                        AgcIndexHelpers.ProsperoIndexType.Index32 =>
+                            BinaryPrimitives.ReadUInt32LittleEndian(
+                                span.Slice(index * sizeof(uint), sizeof(uint))),
+                        AgcIndexHelpers.ProsperoIndexType.Index8 => span[index],
+                        _ => BinaryPrimitives.ReadUInt16LittleEndian(
+                            span.Slice(index * sizeof(ushort), sizeof(ushort))),
+                    };
+                    var restart = indexType switch
+                    {
+                        AgcIndexHelpers.ProsperoIndexType.Index32 => uint.MaxValue,
+                        AgcIndexHelpers.ProsperoIndexType.Index8 => 0xFFu,
+                        _ => ushort.MaxValue,
+                    };
+                    if (value == restart)
                    {
                        // Primitive-restart markers do not address vertex data.
                        continue;
@@ -7372,17 +7474,24 @@ public static partial class AgcExports
        }

        var indexedRecords = sawIndex && maxIndex != uint.MaxValue
-            ? maxIndex + 1
-            : 1u;
+            ? baseVertex + maxIndex + 1
+            : Math.Max(baseVertex + 1, 1u);
        recordCount = Math.Max(indexedRecords, Math.Max(state.InstanceCount, 1u));
        if (_traceVertexRanges &&
            Interlocked.Increment(ref _tracedVertexRangeCount) <= 512)
        {
+            var indexBits = indexType switch
+            {
+                AgcIndexHelpers.ProsperoIndexType.Index32 => 32,
+                AgcIndexHelpers.ProsperoIndexType.Index8 => 8,
+                _ => 16,
+            };
            Console.Error.WriteLine(
                $"[LOADER][TRACE] agc.vertex_range indexed=1 draw_count={drawCount} " +
-                $"max_index={(sawIndex ? maxIndex : 0)} records={recordCount} " +
-                $"instances={state.InstanceCount} index_size={(is32Bit ? 32 : 16)} " +
-                $"index_addr=0x{state.IndexBufferAddress:X16} offset={state.DrawIndexOffset}");
+                $"max_index={(sawIndex ? maxIndex : 0)} base_vertex={baseVertex} " +
+                $"records={recordCount} instances={state.InstanceCount} " +
+                $"index_size={indexBits} index_addr=0x{state.IndexBufferAddress:X16} " +
+                $"offset={state.DrawIndexOffset}");
        }
        return true;
    }
@@ -7392,6 +7501,20 @@ public static partial class AgcExports
            ? (packedMasks >> (int)(target * 4)) & 0xFu
            : 0;

+    private static bool VertexProgramExportsParameters(Gen5ShaderProgram program)
+    {
+        foreach (var instruction in program.Instructions)
+        {
+            if (instruction.Control is Gen5ExportControl export &&
+                export.Target is >= 32 and < 64)
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
    private static uint GetInterpolatedAttributeCount(Gen5ShaderState state)
    {
        var maxAttribute = -1;
@@ -8126,10 +8249,15 @@ public static partial class AgcExports
                    ? $"{entry.Name}=0x{value:X8}"
                    : $"{entry.Name}=missing"));
        var blend = draw.RenderState.Blend;
+        var rectExpanded = AgcPrimitiveHelpers.GetRectListDrawVertexCount(
+            draw.PrimitiveType,
+            draw.VertexCount,
+            indexed: draw.IndexBuffer is not null,
+            hasVertexBuffers: draw.VertexInputs.Count > 0);
        TraceAgcShader(
            $"agc.shader_draw es=0x{draw.ExportShaderAddress:X16} " +
            $"ps=0x{draw.PixelShaderAddress:X16} spirv={draw.PixelShader.Payload.Length} " +
-            $"primitive=0x{draw.PrimitiveType:X} " +
+            $"primitive=0x{draw.PrimitiveType:X} verts={draw.VertexCount}->{rectExpanded} " +
            $"blend={(blend.Enable ? 1 : 0)}:{blend.ColorSrcFactor}/{blend.ColorDstFactor}/{blend.ColorFunc} " +
            $"write_mask=0x{blend.WriteMask:X} scissor={scissor} viewport={viewport} " +
            $"raster=[{raster}] " +
@@ -9415,36 +9543,51 @@ public static partial class AgcExports
        TranslatedGuestDraw draw,
        IReadOnlyList<GuestVertexBuffer> vertexBuffers)
    {
-        if (draw.PrimitiveType != 0x11 ||
-            draw.IndexBuffer is not null ||
-            vertexBuffers.Count == 0 ||
-            _rectListTraceCount >= 8 ||
-            Interlocked.Increment(ref _rectListTraceCount) > 8)
+        if (!AgcPrimitiveHelpers.IsRectListPrimitive(draw.PrimitiveType) ||
+            _rectListTraceCount >= 16 ||
+            Interlocked.Increment(ref _rectListTraceCount) > 16)
        {
            return;
        }

-        var buffer = vertexBuffers[0];
-        var stride = Math.Max(buffer.Stride, 4u);
+        var expanded = AgcPrimitiveHelpers.GetRectListDrawVertexCount(
+            draw.PrimitiveType,
+            draw.VertexCount,
+            indexed: draw.IndexBuffer is not null,
+            hasVertexBuffers: vertexBuffers.Count > 0);
        var text = new System.Text.StringBuilder();
-        for (var vertex = 0; vertex < 3; vertex++)
-        {
-            var baseOffset = (int)(buffer.OffsetBytes + vertex * stride);
-            if (baseOffset + 16 > buffer.Length)
-            {
-                break;
-            }
+        text.Append(
+            $"agc.rectlist prim=0x{draw.PrimitiveType:X} verts={draw.VertexCount}->{expanded} " +
+            $"indexed={(draw.IndexBuffer is not null ? 1 : 0)} vb={vertexBuffers.Count}");

-            var x = BitConverter.ToSingle(buffer.Data, baseOffset);
-            var y = BitConverter.ToSingle(buffer.Data, baseOffset + 4);
-            var z = BitConverter.ToSingle(buffer.Data, baseOffset + 8);
-            var w = BitConverter.ToSingle(buffer.Data, baseOffset + 12);
-            text.Append($" v{vertex}=({x:0.###},{y:0.###},{z:0.###},{w:0.###})");
+        if (vertexBuffers.Count > 0)
+        {
+            var buffer = vertexBuffers[0];
+            var stride = Math.Max(buffer.Stride, 4u);
+            text.Append(
+                $" stride={buffer.Stride} " +
+                $"fmt={buffer.DataFormat}/{buffer.NumberFormat}x{buffer.ComponentCount}");
+            for (var vertex = 0; vertex < 3; vertex++)
+            {
+                var baseOffset = (int)(buffer.OffsetBytes + vertex * stride);
+                if (baseOffset + 16 > buffer.Length)
+                {
+                    break;
+                }
+
+                var x = BitConverter.ToSingle(buffer.Data, baseOffset);
+                var y = BitConverter.ToSingle(buffer.Data, baseOffset + 4);
+                var z = BitConverter.ToSingle(buffer.Data, baseOffset + 8);
+                var w = BitConverter.ToSingle(buffer.Data, baseOffset + 12);
+                text.Append($" v{vertex}=({x:0.###},{y:0.###},{z:0.###},{w:0.###})");
+            }
+        }
+        else
+        {
+            text.Append(" procedural=1");
        }

-        TraceAgcShader(
-            $"agc.rectlist verts={draw.VertexCount} stride={buffer.Stride} " +
-            $"fmt={buffer.DataFormat}/{buffer.NumberFormat}x{buffer.ComponentCount}{text}");
+        TraceAgcShader(text.ToString());
    }

    private static int _textureDumpCount;
@@ -11709,6 +11852,9 @@ public static partial class AgcExports
    private static bool IsEsGeometryShaderType(byte shaderType) =>
        shaderType is 2 or 6;

+    private static bool IsRectListPrimitive(uint primitiveType) =>
+        AgcPrimitiveHelpers.IsRectListPrimitive(primitiveType);
+
    private static int SetIndirectPatchAddress(CpuContext ctx, string registerSpace)
    {
        var commandAddress = ctx[CpuRegister.Rdi];
@@ -0,0 +1,49 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Buffers.Binary;
+
+namespace SharpEmu.Libs.Agc;
+
+/// <summary>Prospero/AGC IndexType helpers (gpu_defs / renderDraw index8 expand).</summary>
+internal static class AgcIndexHelpers
+{
+    internal enum ProsperoIndexType : uint
+    {
+        Index16 = 0,
+        Index32 = 1,
+        Index8 = 2,
+    }
+
+    internal static ProsperoIndexType Decode(uint raw) =>
+        (raw & 0x3u) switch
+        {
+            1 => ProsperoIndexType.Index32,
+            2 => ProsperoIndexType.Index8,
+            _ => ProsperoIndexType.Index16,
+        };
+
+    internal static int GetGuestStrideBytes(ProsperoIndexType indexType) =>
+        indexType switch
+        {
+            ProsperoIndexType.Index32 => sizeof(uint),
+            ProsperoIndexType.Index8 => sizeof(byte),
+            _ => sizeof(ushort),
+        };
+
+    /// <summary>Expand guest u8 indices to host u16 (Vulkan/Metal bindable).</summary>
+    internal static void ExpandIndex8ToU16(ReadOnlySpan<byte> source, Span<byte> destination)
+    {
+        if (destination.Length < source.Length * sizeof(ushort))
+        {
+            throw new ArgumentException("destination too small for u8->u16 expansion.");
+        }
+
+        for (var index = 0; index < source.Length; index++)
+        {
+            BinaryPrimitives.WriteUInt16LittleEndian(
+                destination.Slice(index * sizeof(ushort), sizeof(ushort)),
+                source[index]);
+        }
+    }
+}
@@ -0,0 +1,107 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Libs.Agc;
+
+/// <summary>
+/// Shared Prospero/AGC primitive-type helpers (renderDraw / gpu_defs).
+/// </summary>
+internal static class AgcPrimitiveHelpers
+{
+    internal const uint PrimitiveRectList = 7;
+    internal const uint PrimitiveRectListLegacy = 0x11;
+
+    internal enum GsOutputPrimitiveType : uint
+    {
+        Points = 0,
+        Lines = 1,
+        Triangles = 2,
+        Rectangle2D = 3,
+        RectList = 4,
+    }
+
+    internal static bool IsRectListPrimitive(uint primitiveType) =>
+        primitiveType is PrimitiveRectList or PrimitiveRectListLegacy;
+
+    /// <summary>
+    /// Maps draw prim type to VGT_GS_OUT_PRIM_TYPE when NGG is not enabled
+    /// on the GS (GraphicsPrimitiveTypeToGsOut).
+    /// </summary>
+    internal static uint PrimitiveTypeToGsOut(uint primitiveType) =>
+        primitiveType switch
+        {
+            1 => (uint)GsOutputPrimitiveType.Points, // PointList
+            2 or 3 or 10 or 11 or 18 => (uint)GsOutputPrimitiveType.Lines,
+            PrimitiveRectList => (uint)GsOutputPrimitiveType.Rectangle2D,
+            PrimitiveRectListLegacy => (uint)GsOutputPrimitiveType.RectList,
+            _ => (uint)GsOutputPrimitiveType.Triangles,
+        };
+
+    /// <summary>
+    /// Rect-list auto-draw topology selection.
+    /// NGG single-rect UI quads (DualSense prompts) submit count 1/3/4 and
+    /// must become a 4-vert triangle strip — even when the VS has embedded
+    /// vertex-buffer fetches (those still show up as host VBs). Indexed and
+    /// larger auto counts stay triangle list so the loading video is safe.
+    /// </summary>
+    internal static bool ShouldDrawRectListAsTriangleStrip(
+        uint primitiveType,
+        bool indexed,
+        uint vertexCount,
+        bool hasVertexBuffers = false)
+    {
+        _ = hasVertexBuffers;
+        if (indexed || !IsRectListPrimitive(primitiveType))
+        {
+            return false;
+        }
+
+        if (primitiveType == PrimitiveRectListLegacy)
+        {
+            return true;
+        }
+
+        // NGG kRectList: strip for auto + ngg_rectlist_draw.
+        // Restrict to the single-rect counts GTA UI actually submits.
+        return vertexCount is 1 or 3 or 4;
+    }
+
+    /// <summary>
+    /// Host vertex count for auto rect-list draws that expand to a strip.
+    /// NGG single-rect: always 4. Legacy 0x11: 3 -> 4.
+    /// </summary>
+    internal static uint GetRectListDrawVertexCount(
+        uint primitiveType,
+        uint vertexCount,
+        bool indexed,
+        bool hasVertexBuffers = false)
+    {
+        if (!ShouldDrawRectListAsTriangleStrip(
+                primitiveType,
+                indexed,
+                vertexCount,
+                hasVertexBuffers))
+        {
+            return vertexCount;
+        }
+
+        if (primitiveType == PrimitiveRectList)
+        {
+            return 4;
+        }
+
+        if (primitiveType == PrimitiveRectListLegacy && vertexCount == 3)
+        {
+            return 4;
+        }
+
+        return vertexCount;
+    }
+
+    /// <summary>
+    /// Legacy helper — prefer
+    /// <see cref="ShouldDrawRectListAsTriangleStrip"/>.
+    /// </summary>
+    internal static bool IsRectListTriangleStrip(uint primitiveType) =>
+        IsRectListPrimitive(primitiveType);
+}
@@ -109,7 +109,8 @@ internal interface IGuestGpuBackend
        GuestIndexBuffer? indexBuffer = null,
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
-        ulong shaderAddress = 0);
+        ulong shaderAddress = 0,
+        int baseVertex = 0);

    void SubmitOffscreenTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -125,7 +126,8 @@ internal interface IGuestGpuBackend
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
        GuestDepthTarget? depthTarget = null,
-        ulong shaderAddress = 0);
+        ulong shaderAddress = 0,
+        int baseVertex = 0);

    void SubmitStorageTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -253,7 +253,8 @@ internal sealed class MetalGuestGpuBackend : IGuestGpuBackend
        GuestIndexBuffer? indexBuffer = null,
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
-        ulong shaderAddress = 0) =>
+        ulong shaderAddress = 0,
+        int baseVertex = 0) =>
        MetalVideoPresenter.SubmitDepthOnlyTranslatedDraw(
            Msl(pixelShader),
            textures,
@@ -267,7 +268,8 @@ internal sealed class MetalGuestGpuBackend : IGuestGpuBackend
            indexBuffer,
            vertexBuffers,
            renderState,
-            shaderAddress);
+            shaderAddress,
+            baseVertex);

    public void SubmitOffscreenTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -283,7 +285,8 @@ internal sealed class MetalGuestGpuBackend : IGuestGpuBackend
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
        GuestDepthTarget? depthTarget = null,
-        ulong shaderAddress = 0) =>
+        ulong shaderAddress = 0,
+        int baseVertex = 0) =>
        MetalVideoPresenter.SubmitOffscreenTranslatedDraw(
            Msl(pixelShader),
            textures,
@@ -298,7 +301,8 @@ internal sealed class MetalGuestGpuBackend : IGuestGpuBackend
            vertexBuffers,
            renderState,
            depthTarget,
-            shaderAddress);
+            shaderAddress,
+            baseVertex);

    public void SubmitStorageTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -1,6 +1,7 @@
 // Copyright (C) 2026 SharpEmu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later

+using System.Buffers.Binary;
 using SharpEmu.Libs.Agc;
 using SharpEmu.ShaderCompiler;
 using SharpEmu.ShaderCompiler.Metal;
@@ -87,7 +88,8 @@ internal static partial class MetalVideoPresenter
        uint InstanceCount,
        uint PrimitiveType,
        GuestIndexBuffer? IndexBuffer,
-        GuestRenderState RenderState);
+        GuestRenderState RenderState,
+        int BaseVertex = 0);

    private sealed record OffscreenGuestDraw(
        TranslatedGuestDraw Draw,
@@ -245,7 +247,8 @@ internal static partial class MetalVideoPresenter
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers,
        GuestRenderState? renderState,
        GuestDepthTarget? depthTarget,
-        ulong shaderAddress)
+        ulong shaderAddress,
+        int baseVertex = 0)
    {
        if (targets.Count == 0)
        {
@@ -293,7 +296,8 @@ internal static partial class MetalVideoPresenter
                        instanceCount,
                        primitiveType,
                        indexBuffer,
-                        effectiveRenderState),
+                        effectiveRenderState,
+                        baseVertex),
                    ToArray(targets),
                    depthTarget,
                    PublishTarget: true,
@@ -321,7 +325,8 @@ internal static partial class MetalVideoPresenter
        GuestIndexBuffer? indexBuffer,
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers,
        GuestRenderState? renderState,
-        ulong shaderAddress)
+        ulong shaderAddress,
+        int baseVertex = 0)
    {
        if (depthTarget.Address == 0 || depthTarget.Width == 0 || depthTarget.Height == 0)
        {
@@ -348,7 +353,8 @@ internal static partial class MetalVideoPresenter
                        instanceCount,
                        primitiveType,
                        indexBuffer,
-                        renderState ?? GuestRenderState.Default),
+                        renderState ?? GuestRenderState.Default,
+                        baseVertex),
                    [new GuestRenderTarget(Address: 0, depthTarget.Width, depthTarget.Height, Format: 10, NumberType: 0)],
                    depthTarget,
                    PublishTarget: false,
@@ -981,17 +987,38 @@ internal static partial class MetalVideoPresenter

    private static void EncodeDrawCall(nint encoder, TranslatedGuestDraw draw)
    {
-        var primitive = GetPrimitiveType(draw.PrimitiveType);
-        var vertexCount = draw.PrimitiveType == 0x11 && draw.IndexBuffer is null
-            ? 4u
-            : draw.VertexCount;
+        var indexed = draw.IndexBuffer is not null;
+        var hasVertexBuffers = draw.VertexBuffers.Length > 0;
+        var primitive = GetPrimitiveType(
+            draw.PrimitiveType,
+            indexed,
+            draw.VertexCount,
+            hasVertexBuffers);
+        var vertexCount = AgcPrimitiveHelpers.GetRectListDrawVertexCount(
+            draw.PrimitiveType,
+            draw.VertexCount,
+            indexed,
+            hasVertexBuffers);
+        var baseVertex = (nuint)Math.Max(draw.BaseVertex, 0);
        if (draw.IndexBuffer is { } indexBuffer)
        {
            var device = MetalNative.Send(encoder, MetalNative.Selector("device"));
            var slice = AllocateUpload(
                device, Math.Max(indexBuffer.Length, 1), out var buffer, out var offset);
-            indexBuffer.Data.AsSpan(0, Math.Min(indexBuffer.Length, indexBuffer.Data.Length))
-                .CopyTo(slice);
+            var source = indexBuffer.Data.AsSpan(
+                0,
+                Math.Min(indexBuffer.Length, indexBuffer.Data.Length));
+            // Metal drawIndexed without baseVertex: bake GE_INDX_OFFSET into
+            // the uploaded indices so glyph batches still hit the right verts.
+            if (draw.BaseVertex != 0)
+            {
+                BakeBaseVertexIntoIndices(source, slice, indexBuffer.Is32Bit, draw.BaseVertex);
+            }
+            else
+            {
+                source.CopyTo(slice);
+            }
+
            MetalNative.SendDrawIndexedPrimitives(
                encoder,
                MetalNative.Selector("drawIndexedPrimitives:indexCount:indexType:indexBuffer:indexBufferOffset:instanceCount:"),
@@ -1012,12 +1039,46 @@ internal static partial class MetalVideoPresenter
                encoder,
                MetalNative.Selector("drawPrimitives:vertexStart:vertexCount:instanceCount:"),
                primitive,
-                0,
+                baseVertex,
                vertexCount,
                Math.Max(draw.InstanceCount, 1));
        }
    }

+    private static void BakeBaseVertexIntoIndices(
+        ReadOnlySpan<byte> source,
+        Span<byte> destination,
+        bool is32Bit,
+        int baseVertex)
+    {
+        if (is32Bit)
+        {
+            var count = source.Length / sizeof(uint);
+            for (var index = 0; index < count; index++)
+            {
+                var value = BinaryPrimitives.ReadUInt32LittleEndian(
+                    source.Slice(index * sizeof(uint), sizeof(uint)));
+                var adjusted = unchecked((uint)(value + baseVertex));
+                BinaryPrimitives.WriteUInt32LittleEndian(
+                    destination.Slice(index * sizeof(uint), sizeof(uint)),
+                    adjusted);
+            }
+
+            return;
+        }
+
+        var shortCount = source.Length / sizeof(ushort);
+        for (var index = 0; index < shortCount; index++)
+        {
+            var value = BinaryPrimitives.ReadUInt16LittleEndian(
+                source.Slice(index * sizeof(ushort), sizeof(ushort)));
+            var adjusted = unchecked((ushort)(value + baseVertex));
+            BinaryPrimitives.WriteUInt16LittleEndian(
+                destination.Slice(index * sizeof(ushort), sizeof(ushort)),
+                adjusted);
+        }
+    }
+
    private static bool TryGetDrawPipeline(
        nint device,
        TranslatedGuestDraw draw,
@@ -2062,13 +2123,30 @@ internal static partial class MetalVideoPresenter

                return 3;
            case 6:
-            case 0x11:
                return 4;
            default:
                return 3;
        }
    }

+    private static nuint GetPrimitiveType(
+        uint guestPrimitiveType,
+        bool indexed,
+        uint vertexCount,
+        bool hasVertexBuffers)
+    {
+        if (AgcPrimitiveHelpers.ShouldDrawRectListAsTriangleStrip(
+                guestPrimitiveType,
+                indexed,
+                vertexCount,
+                hasVertexBuffers))
+        {
+            return 4; // MTLPrimitiveTypeTriangleStrip
+        }
+
+        return GetPrimitiveType(guestPrimitiveType);
+    }
+
    private static bool IsIntegerFormat(Gen5PixelOutputKind kind) =>
        kind is Gen5PixelOutputKind.Uint or Gen5PixelOutputKind.Sint;

@@ -181,7 +181,8 @@ internal sealed class VulkanGuestGpuBackend : IGuestGpuBackend
        GuestIndexBuffer? indexBuffer = null,
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
-        ulong shaderAddress = 0) =>
+        ulong shaderAddress = 0,
+        int baseVertex = 0) =>
        VulkanVideoPresenter.SubmitDepthOnlyTranslatedDraw(
            Spirv(pixelShader),
            textures,
@@ -195,7 +196,8 @@ internal sealed class VulkanGuestGpuBackend : IGuestGpuBackend
            indexBuffer,
            vertexBuffers,
            renderState,
-            shaderAddress);
+            shaderAddress,
+            baseVertex);

    public void SubmitOffscreenTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -211,7 +213,8 @@ internal sealed class VulkanGuestGpuBackend : IGuestGpuBackend
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
        GuestDepthTarget? depthTarget = null,
-        ulong shaderAddress = 0) =>
+        ulong shaderAddress = 0,
+        int baseVertex = 0) =>
        VulkanVideoPresenter.SubmitOffscreenTranslatedDraw(
            Spirv(pixelShader),
            textures,
@@ -226,7 +229,8 @@ internal sealed class VulkanGuestGpuBackend : IGuestGpuBackend
            vertexBuffers,
            renderState,
            depthTarget,
-            shaderAddress);
+            shaderAddress,
+            baseVertex);

    public void SubmitStorageTranslatedDraw(
        IGuestCompiledShader pixelShader,
@@ -45,7 +45,8 @@ internal sealed record VulkanTranslatedGuestDraw(
    uint InstanceCount,
    uint PrimitiveType,
    GuestIndexBuffer? IndexBuffer,
-    GuestRenderState RenderState);
+    GuestRenderState RenderState,
+    int BaseVertex = 0);

 internal sealed record VulkanOffscreenGuestDraw(
    VulkanTranslatedGuestDraw Draw,
@@ -469,7 +470,8 @@ internal static unsafe class VulkanVideoPresenter
        uint.TryParse(Environment.GetEnvironmentVariable("SHARPEMU_SKIP_TALL_COMPUTE_Z"), out var z)
            ? z
            : 0;
-    private const uint GuestPrimitiveRectList = 0x11;
+    private const uint GuestPrimitiveRectList = AgcPrimitiveHelpers.PrimitiveRectListLegacy;
+    private const uint GuestPrimitiveRectListNgg = AgcPrimitiveHelpers.PrimitiveRectList;

    private static readonly object _gate = new();
    private readonly record struct PendingGuestWork(
@@ -1029,7 +1031,8 @@ internal static unsafe class VulkanVideoPresenter
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
        GuestDepthTarget? depthTarget = null,
-        ulong shaderAddress = 0)
+        ulong shaderAddress = 0,
+        int baseVertex = 0)
    {
        SubmitOffscreenTranslatedDraw(
            pixelSpirv,
@@ -1045,7 +1048,8 @@ internal static unsafe class VulkanVideoPresenter
            vertexBuffers,
            renderState,
            depthTarget,
-            shaderAddress);
+            shaderAddress,
+            baseVertex);
    }

    // Manual scans (targets are <= 8) so the per-draw validation does not
@@ -1098,7 +1102,8 @@ internal static unsafe class VulkanVideoPresenter
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
        GuestDepthTarget? depthTarget = null,
-        ulong shaderAddress = 0)
+        ulong shaderAddress = 0,
+        int baseVertex = 0)
    {
        if (pixelSpirv.Length == 0 ||
            targets.Count == 0 ||
@@ -1165,7 +1170,8 @@ internal static unsafe class VulkanVideoPresenter
                        instanceCount,
                        primitiveType,
                        indexBuffer,
-                        effectiveRenderState),
+                        effectiveRenderState,
+                        baseVertex),
                    targets.ToArray(),
                    depthTarget,
                    PublishTarget: true,
@@ -1190,7 +1196,8 @@ internal static unsafe class VulkanVideoPresenter
        GuestIndexBuffer? indexBuffer = null,
        IReadOnlyList<GuestVertexBuffer>? vertexBuffers = null,
        GuestRenderState? renderState = null,
-        ulong shaderAddress = 0)
+        ulong shaderAddress = 0,
+        int baseVertex = 0)
    {
        if (pixelSpirv.Length == 0 ||
            depthTarget.Address == 0 ||
@@ -1220,7 +1227,8 @@ internal static unsafe class VulkanVideoPresenter
                        instanceCount,
                        primitiveType,
                        indexBuffer,
-                        renderState ?? GuestRenderState.Default),
+                        renderState ?? GuestRenderState.Default,
+                        baseVertex),
                    [new GuestRenderTarget(
                        Address: 0,
                        depthTarget.Width,
@@ -3129,6 +3137,7 @@ internal static unsafe class VulkanVideoPresenter
            public bool Index32Bit;
            public uint VertexCount = 3;
            public uint InstanceCount = 1;
+            public int BaseVertex;
            public PrimitiveTopology Topology = PrimitiveTopology.TriangleList;
            public GuestBlendState[] Blends = [GuestBlendState.Default];
            public GuestBlendConstant BlendConstant;
@@ -6190,9 +6199,18 @@ internal static unsafe class VulkanVideoPresenter
                GlobalMemoryBuffers =
                    new GlobalBufferResource[draw.GlobalMemoryBuffers.Count],
                VertexBuffers = new VertexBufferResource[draw.VertexBuffers.Count],
-                VertexCount = GetDrawVertexCount(draw.PrimitiveType, draw.VertexCount, draw.IndexBuffer),
+                VertexCount = GetDrawVertexCount(
+                    draw.PrimitiveType,
+                    draw.VertexCount,
+                    draw.IndexBuffer,
+                    draw.VertexBuffers.Count > 0),
                InstanceCount = Math.Max(draw.InstanceCount, 1),
-                Topology = GetPrimitiveTopology(draw.PrimitiveType),
+                BaseVertex = draw.BaseVertex,
+                Topology = GetPrimitiveTopology(
+                    draw.PrimitiveType,
+                    indexed: draw.IndexBuffer is not null,
+                    vertexCount: draw.VertexCount,
+                    hasVertexBuffers: draw.VertexBuffers.Count > 0),
                Blends = draw.RenderState.Blends.ToArray(),
                BlendConstant = draw.RenderState.BlendConstant,
                Scissor = draw.RenderState.Scissor,
@@ -9680,7 +9698,11 @@ internal static unsafe class VulkanVideoPresenter
            _vk.FreeMemory(_device, allocation.Memory, null);
        }

-        private static PrimitiveTopology GetPrimitiveTopology(uint primitiveType) =>
+        private static PrimitiveTopology GetPrimitiveTopology(
+            uint primitiveType,
+            bool indexed,
+            uint vertexCount,
+            bool hasVertexBuffers) =>
            primitiveType switch
            {
                1 => PrimitiveTopology.PointList,
@@ -9688,7 +9710,12 @@ internal static unsafe class VulkanVideoPresenter
                3 => PrimitiveTopology.LineStrip,
                5 => PrimitiveTopology.TriangleFan,
                6 => PrimitiveTopology.TriangleStrip,
-                GuestPrimitiveRectList => PrimitiveTopology.TriangleStrip,
+                GuestPrimitiveRectListNgg or GuestPrimitiveRectList
+                    when AgcPrimitiveHelpers.ShouldDrawRectListAsTriangleStrip(
+                        primitiveType,
+                        indexed,
+                        vertexCount,
+                        hasVertexBuffers) => PrimitiveTopology.TriangleStrip,
                _ => PrimitiveTopology.TriangleList,
            };

@@ -9846,15 +9873,13 @@ internal static unsafe class VulkanVideoPresenter
        private static uint GetDrawVertexCount(
            uint primitiveType,
            uint vertexCount,
-            GuestIndexBuffer? indexBuffer)
-        {
-            if (primitiveType == GuestPrimitiveRectList && indexBuffer is null)
-            {
-                return 4;
-            }
-
-            return vertexCount;
-        }
+            GuestIndexBuffer? indexBuffer,
+            bool hasVertexBuffers) =>
+            AgcPrimitiveHelpers.GetRectListDrawVertexCount(
+                primitiveType,
+                vertexCount,
+                indexed: indexBuffer is not null,
+                hasVertexBuffers);

        private static BlendFactor ToVkBlendFactor(uint factor) =>
            factor switch
@@ -15737,12 +15762,14 @@ internal static unsafe class VulkanVideoPresenter
                        resources.IndexBuffer,
                        0,
                        resources.Index32Bit ? IndexType.Uint32 : IndexType.Uint16);
+                    // vertexOffset = ResolveVertexOffset(GE_INDX_OFFSET).
+                    // GTA UI glyphs use relative indices + a nonzero base vertex.
                    _vk.CmdDrawIndexed(
                        _commandBuffer,
                        resources.VertexCount,
                        resources.InstanceCount,
                        0,
-                        0,
+                        resources.BaseVertex,
                        0);
                }
                else
@@ -15751,7 +15778,7 @@ internal static unsafe class VulkanVideoPresenter
                        _commandBuffer,
                        resources.VertexCount,
                        resources.InstanceCount,
-                        0,
+                        (uint)Math.Max(resources.BaseVertex, 0),
                        0);
                }

@@ -0,0 +1,95 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Buffers.Binary;
+using SharpEmu.Libs.Agc;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.Agc;
+
+/// <summary>
+/// Regression coverage for the AGC UI path: index8 expansion and rect-list
+/// vertex counts / topology selection.
+/// </summary>
+public sealed class AgcRectListIndexHelpersTests
+{
+    [Theory]
+    [InlineData(0u, 0u, 2)] // Index16
+    [InlineData(1u, 1u, 4)] // Index32
+    [InlineData(2u, 2u, 1)] // Index8
+    [InlineData(0x402u, 2u, 1)] // UC 0x400|size -> Index8
+    public void IndexType_DecodeAndStride_MatchProspero(uint raw, uint expected, int stride)
+    {
+        var decoded = AgcIndexHelpers.Decode(raw);
+        Assert.Equal((AgcIndexHelpers.ProsperoIndexType)expected, decoded);
+        Assert.Equal(stride, AgcIndexHelpers.GetGuestStrideBytes(decoded));
+    }
+
+    [Fact]
+    public void ExpandIndex8ToU16_PreservesValues()
+    {
+        ReadOnlySpan<byte> source = [0x00, 0x01, 0xFF, 0x7F];
+        Span<byte> destination = stackalloc byte[8];
+        AgcIndexHelpers.ExpandIndex8ToU16(source, destination);
+        Assert.Equal(0, BinaryPrimitives.ReadUInt16LittleEndian(destination[..2]));
+        Assert.Equal(1, BinaryPrimitives.ReadUInt16LittleEndian(destination.Slice(2, 2)));
+        Assert.Equal(255, BinaryPrimitives.ReadUInt16LittleEndian(destination.Slice(4, 2)));
+        Assert.Equal(127, BinaryPrimitives.ReadUInt16LittleEndian(destination.Slice(6, 2)));
+    }
+
+    [Theory]
+    // NGG single-rect UI (DualSense): expand even when VBs are present
+    [InlineData(7u, 3u, false, true, 4u)]
+    [InlineData(7u, 1u, false, false, 4u)]
+    [InlineData(7u, 4u, false, true, 4u)]
+    // Indexed / multi-vert auto: keep guest count (loading video)
+    [InlineData(7u, 3u, true, false, 3u)]
+    [InlineData(7u, 6u, false, true, 6u)]
+    [InlineData(7u, 4u, true, true, 4u)]
+    [InlineData(0x11u, 3u, false, false, 4u)]
+    [InlineData(0x11u, 6u, false, false, 6u)]
+    [InlineData(4u, 3u, false, false, 3u)]
+    public void RectListDrawVertexCount_MatchesExpansion(
+        uint primitiveType,
+        uint vertexCount,
+        bool indexed,
+        bool hasVertexBuffers,
+        uint expected)
+    {
+        Assert.Equal(
+            expected,
+            AgcPrimitiveHelpers.GetRectListDrawVertexCount(
+                primitiveType,
+                vertexCount,
+                indexed,
+                hasVertexBuffers));
+    }
+
+    [Theory]
+    [InlineData(7u, false, 3u, true, true)]
+    [InlineData(7u, false, 6u, true, false)]
+    [InlineData(7u, true, 3u, false, false)]
+    [InlineData(0x11u, false, 3u, true, true)]
+    [InlineData(0x11u, true, 3u, false, false)]
+    public void RectListTriangleStrip_MatchesGuards(
+        uint primitiveType,
+        bool indexed,
+        uint vertexCount,
+        bool hasVertexBuffers,
+        bool expected) =>
+        Assert.Equal(
+            expected,
+            AgcPrimitiveHelpers.ShouldDrawRectListAsTriangleStrip(
+                primitiveType,
+                indexed,
+                vertexCount,
+                hasVertexBuffers));
+
+    [Theory]
+    [InlineData(7u, (uint)AgcPrimitiveHelpers.GsOutputPrimitiveType.Rectangle2D)]
+    [InlineData(0x11u, (uint)AgcPrimitiveHelpers.GsOutputPrimitiveType.RectList)]
+    [InlineData(4u, (uint)AgcPrimitiveHelpers.GsOutputPrimitiveType.Triangles)]
+    [InlineData(1u, (uint)AgcPrimitiveHelpers.GsOutputPrimitiveType.Points)]
+    public void PrimitiveTypeToGsOut_MatchesProspero(uint primitiveType, uint expected) =>
+        Assert.Equal(expected, AgcPrimitiveHelpers.PrimitiveTypeToGsOut(primitiveType));
+}