feat(render): Phase A8 — IndoorCellStencilPipeline + PortalMeshBuilder
The pipeline class owns the portal_stencil shader + a dynamic VBO/VAO for per-frame portal triangle uploads. MarkAndPunch runs WB's two-step stencil setup (mark portals = 1, then write gl_FragDepth=1.0 into stencil=1 regions). EnableOutdoorPass switches to read-only stencil for the subsequent terrain + outdoor-entity passes. PortalMeshBuilder.BuildTriangles is the pure-math triangle-fan extractor — unit-testable without a GL context. Only exit portals (OtherCellId == 0xFFFF) are emitted; inner portals are skipped to prevent outdoor geometry from bleeding into adjacent rooms. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Erik
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249
src/AcDream.App/Rendering/IndoorCellStencilPipeline.cs
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src/AcDream.App/Rendering/IndoorCellStencilPipeline.cs
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// IndoorCellStencilPipeline.cs — Phase A8 indoor-cell visibility culling.
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//
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// Ports WorldBuilder's RenderInsideOut stencil mechanism for acdream's
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// modern GL pipeline. Closes issue #78 (outdoor stabs visible through
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// indoor walls) and the cellar-stairs artifact (outdoor terrain visible
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// inside cottage cellars).
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//
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// Algorithm (per WB VisibilityManager.cs:73-239):
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// Step 1: stencil ref=1 marked everywhere portal polygons cover
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// (color/depth writes off, depth=Always, CullFace off).
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// Step 2: gl_FragDepth=1.0 punched into stencil=1 regions
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// (color off, depth on, depth=Always).
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// Step 3: (caller) draw indoor entities with stencil OFF.
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// Step 4: (caller) draw terrain + outdoor entities with
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// glStencilFunc(Equal, 1, 0x01), stencil read-only.
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//
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// Retail equivalent: PView::DrawCells at
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// docs/research/named-retail/acclient_2013_pseudo_c.txt:432709 uses
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// screen-space polygon-clip scissor instead of stencil. Same observable
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// behavior; the stencil approach matches modern GL pipeline conventions.
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using System;
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using System.Collections.Generic;
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using System.Numerics;
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using Silk.NET.OpenGL;
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namespace AcDream.App.Rendering;
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/// <summary>
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/// Pure-math triangle-fan generation from a list of cells with
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/// <see cref="LoadedCell.PortalPolygons"/>. Extracted as a static class so
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/// the vertex-list construction is unit-testable without a GL context.
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/// </summary>
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public static class PortalMeshBuilder
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{
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/// <summary>
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/// Builds a flat triangle-fan vertex array in world space from every
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/// exit portal (<see cref="CellPortalInfo.OtherCellId"/> == 0xFFFF) on
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/// every cell in <paramref name="cells"/>. Inner portals are skipped
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/// — they don't open to outdoors, so stencil-marking them would let
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/// outdoor geometry bleed into adjacent rooms (incorrect).
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/// </summary>
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public static Vector3[] BuildTriangles(IReadOnlyCollection<LoadedCell> cells)
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{
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// Pre-count to size the output exactly.
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int triCount = 0;
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foreach (var cell in cells)
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{
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for (int p = 0; p < cell.Portals.Count; p++)
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{
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if (cell.Portals[p].OtherCellId != 0xFFFF) continue;
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if (p >= cell.PortalPolygons.Count) continue;
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var poly = cell.PortalPolygons[p];
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if (poly.Length < 3) continue;
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triCount += (poly.Length - 2) * 3;
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}
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}
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if (triCount == 0) return Array.Empty<Vector3>();
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var output = new Vector3[triCount];
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int outIdx = 0;
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foreach (var cell in cells)
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{
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var xform = cell.WorldTransform;
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for (int p = 0; p < cell.Portals.Count; p++)
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{
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if (cell.Portals[p].OtherCellId != 0xFFFF) continue;
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if (p >= cell.PortalPolygons.Count) continue;
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var poly = cell.PortalPolygons[p];
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if (poly.Length < 3) continue;
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// Triangle-fan from vertex 0.
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var v0 = Vector3.Transform(poly[0], xform);
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for (int i = 1; i < poly.Length - 1; i++)
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{
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output[outIdx++] = v0;
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output[outIdx++] = Vector3.Transform(poly[i], xform);
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output[outIdx++] = Vector3.Transform(poly[i + 1], xform);
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}
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}
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}
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return output;
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}
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}
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/// <summary>
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/// GL pipeline owner. Holds the portal stencil shader and a dynamic
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/// VBO/VAO for per-frame portal triangle uploads. Public methods are
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/// called in the per-frame render path when the camera is inside an
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/// EnvCell. When outside, this object is dormant — no GL work.
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/// </summary>
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public sealed unsafe class IndoorCellStencilPipeline : IDisposable
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{
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private readonly GL _gl;
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private readonly Shader _shader;
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private readonly uint _vao;
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private readonly uint _vbo;
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private int _vboCapacityVerts;
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private int _lastVertexCount;
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private int _uViewProjectionLoc;
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private int _uWriteFarDepthLoc;
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public IndoorCellStencilPipeline(GL gl, string vertPath, string fragPath)
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{
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_gl = gl;
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_shader = new Shader(gl, vertPath, fragPath);
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_uViewProjectionLoc = _gl.GetUniformLocation(_shader.Program, "uViewProjection");
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_uWriteFarDepthLoc = _gl.GetUniformLocation(_shader.Program, "uWriteFarDepth");
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_vao = _gl.GenVertexArray();
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_vbo = _gl.GenBuffer();
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AllocateVbo(1024);
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ConfigureVao();
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}
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/// <summary>
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/// Builds the per-frame portal triangle array from <paramref name="cells"/>
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/// and uploads it to <see cref="_vbo"/>. Returns the vertex count
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/// (0 means no exit portals — caller should skip stencil setup entirely).
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/// </summary>
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public int UploadPortalMesh(IReadOnlyCollection<LoadedCell> cells)
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{
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var verts = PortalMeshBuilder.BuildTriangles(cells);
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_lastVertexCount = verts.Length;
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if (_lastVertexCount == 0) return 0;
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if (_lastVertexCount > _vboCapacityVerts)
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{
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_vboCapacityVerts = Math.Max(_lastVertexCount * 2, 1024);
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AllocateVbo(_vboCapacityVerts);
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}
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_gl.BindBuffer(BufferTargetARB.ArrayBuffer, _vbo);
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fixed (Vector3* p = verts)
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{
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_gl.BufferSubData(BufferTargetARB.ArrayBuffer, 0,
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(nuint)(_lastVertexCount * sizeof(Vector3)), p);
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}
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_gl.BindBuffer(BufferTargetARB.ArrayBuffer, 0);
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return _lastVertexCount;
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}
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/// <summary>
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/// Steps 1+2 of WB's RenderInsideOut: mark stencil ref=1 wherever
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/// portal polygons cover, then write gl_FragDepth=1.0 into those
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/// regions. Leaves the GL state set up for the caller to invoke
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/// <see cref="EnableOutdoorPass"/>.
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/// </summary>
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public void MarkAndPunch(Matrix4x4 viewProjection)
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{
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if (_lastVertexCount == 0) return;
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_gl.Enable(EnableCap.StencilTest);
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_gl.ClearStencil(0);
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_gl.Clear(ClearBufferMask.StencilBufferBit);
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// Step 1: stencil mark.
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_gl.ColorMask(false, false, false, false);
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_gl.DepthMask(false);
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_gl.DepthFunc(DepthFunction.Always);
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_gl.Disable(EnableCap.CullFace);
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_gl.Enable(EnableCap.DepthClamp); // portal polys can be at any Z
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_gl.StencilFunc(StencilFunction.Always, 1, 0xFFu);
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_gl.StencilMask(0x01u);
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_gl.StencilOp(StencilOp.Keep, StencilOp.Keep, StencilOp.Replace);
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_shader.Use();
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var vp = viewProjection;
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_gl.UniformMatrix4(_uViewProjectionLoc, 1, false, (float*)&vp);
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_gl.Uniform1(_uWriteFarDepthLoc, 0);
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_gl.BindVertexArray(_vao);
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_gl.DrawArrays(PrimitiveType.Triangles, 0, (uint)_lastVertexCount);
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// Step 2: far-depth punch.
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_gl.ColorMask(false, false, false, false);
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_gl.DepthMask(true);
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_gl.DepthFunc(DepthFunction.Always);
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_gl.StencilFunc(StencilFunction.Equal, 1, 0x01u);
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_gl.StencilMask(0x00u); // read-only
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_gl.StencilOp(StencilOp.Keep, StencilOp.Keep, StencilOp.Keep);
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_gl.Uniform1(_uWriteFarDepthLoc, 1);
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_gl.DrawArrays(PrimitiveType.Triangles, 0, (uint)_lastVertexCount);
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_gl.BindVertexArray(0);
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_gl.Disable(EnableCap.DepthClamp);
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_gl.Enable(EnableCap.CullFace);
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// Leave a clean state for the indoor-entities pass: stencil
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// disabled, color+depth on, depth=Less, no cull change.
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_gl.ColorMask(true, true, true, true);
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_gl.DepthFunc(DepthFunction.Less);
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_gl.Disable(EnableCap.StencilTest);
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}
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/// <summary>
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/// Step 4 of WB's RenderInsideOut: enable stencil read-only with
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/// ref=1, so subsequent terrain + outdoor entity draws are gated
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/// to portal silhouette regions only.
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/// </summary>
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public void EnableOutdoorPass()
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{
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if (_lastVertexCount == 0) return;
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_gl.Enable(EnableCap.StencilTest);
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_gl.StencilFunc(StencilFunction.Equal, 1, 0x01u);
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_gl.StencilMask(0x00u);
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_gl.StencilOp(StencilOp.Keep, StencilOp.Keep, StencilOp.Keep);
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}
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/// <summary>
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/// Restores stencil-off state. Call after all outdoor passes complete
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/// so subsequent rendering (particles, sky, UI) is unaffected.
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/// </summary>
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public void DisableStencil()
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{
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_gl.Disable(EnableCap.StencilTest);
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_gl.StencilMask(0xFFu); // restore default write mask
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}
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public void Dispose()
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{
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_shader.Dispose();
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_gl.DeleteVertexArray(_vao);
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_gl.DeleteBuffer(_vbo);
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}
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private void AllocateVbo(int capacityVerts)
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{
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_vboCapacityVerts = capacityVerts;
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_gl.BindBuffer(BufferTargetARB.ArrayBuffer, _vbo);
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_gl.BufferData(BufferTargetARB.ArrayBuffer,
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(nuint)(capacityVerts * sizeof(Vector3)),
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null, BufferUsageARB.DynamicDraw);
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_gl.BindBuffer(BufferTargetARB.ArrayBuffer, 0);
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}
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private void ConfigureVao()
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{
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_gl.BindVertexArray(_vao);
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_gl.BindBuffer(BufferTargetARB.ArrayBuffer, _vbo);
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_gl.EnableVertexAttribArray(0);
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_gl.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false,
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(uint)sizeof(Vector3), (void*)0);
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_gl.BindVertexArray(0);
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}
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}
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