phase(N.5) Task 15: delete legacy mesh_instanced shader files

mesh_instanced.vert + .frag deleted. WbDrawDispatcher always uses
mesh_modern when WB foundation is on. Legacy escape hatch
(ACDREAM_USE_WB_FOUNDATION=0 or bindless missing) runs through
InstancedMeshRenderer which has its own shader path — untouched.

GameWindow's else-branch removed; if bindless is missing, _meshShader
stays unloaded, _wbDrawDispatcher stays null, and _staticMesh is not
constructed (its guard requires _meshShader non-null). All downstream
_staticMesh usages were already null-safe (null-conditional operators
or explicit null guards). Two null-forgiving suppressors added at the
WbDrawDispatcher + SkyRenderer construction sites where the compiler
couldn't prove non-null but the logic guarantees it (both require
_bindlessSupport non-null, which implies _meshShader was assigned;
_textureCache is assigned unconditionally).

InstancedMeshRenderer.cs: the one reference to mesh_instanced was
a code comment (location 3 NOT used by mesh_instanced.vert) — not
a file load. Escape hatch code path is preserved; the shader comment
is now stale but low priority.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -1447,9 +1447,11 @@ public sealed class GameWindow : IDisposable
             }
         }
 
-        // N.5 Task 10: load mesh_modern when both extensions are present;
+        // N.5 Task 10/15: load mesh_modern when both extensions are present.
-        // fall back to mesh_instanced otherwise. Must be after capability
+        // If bindless is missing _meshShader stays null, _wbDrawDispatcher won't
-        // detection so _bindlessSupport is known.
+        // be constructed (its guard requires _bindlessSupport non-null), and
+        // rendering falls back to InstancedMeshRenderer — but only when
+        // _meshShader is non-null (see _staticMesh construction below).
         if (_bindlessSupport is not null)
         {
             _meshShader = new Shader(_gl,
@@ -1457,12 +1459,7 @@ public sealed class GameWindow : IDisposable
                 Path.Combine(shadersDir, "mesh_modern.frag"));
             Console.WriteLine("[N.5] mesh_modern shader loaded");
         }
-        else
+        // else: bindless missing — _meshShader stays null.
-        {
-            _meshShader = new Shader(_gl,
-                Path.Combine(shadersDir, "mesh_instanced.vert"),
-                Path.Combine(shadersDir, "mesh_instanced.frag"));
-        }
 
         _textureCache = new TextureCache(_gl, _dats, _bindlessSupport);
         // Two persistent GL sampler objects (Repeat + ClampToEdge) so
@@ -1538,14 +1535,21 @@ public sealed class GameWindow : IDisposable
             _worldState = new AcDream.App.Streaming.GpuWorldState(wbSpawnAdapter, wbEntitySpawnAdapter);
         }
 
-        _staticMesh = new InstancedMeshRenderer(_gl, _meshShader, _textureCache, _wbMeshAdapter);
+        // Task 15: _meshShader is null when bindless is missing; skip constructing
+        // _staticMesh in that case. All downstream _staticMesh usages are already
+        // null-safe (null-conditional operators or explicit null guards).
+        if (_meshShader is not null && _textureCache is not null)
+            _staticMesh = new InstancedMeshRenderer(_gl, _meshShader, _textureCache, _wbMeshAdapter);
 
         if (AcDream.App.Rendering.Wb.WbFoundationFlag.IsEnabled
             && _wbMeshAdapter is not null && _wbEntitySpawnAdapter is not null
             && _bindlessSupport is not null)
         {
+            // _meshShader is non-null here: the _bindlessSupport guard implies
+            // the if(_bindlessSupport is not null) block above ran and assigned it.
+            // _textureCache is always non-null (assigned unconditionally above).
             _wbDrawDispatcher = new AcDream.App.Rendering.Wb.WbDrawDispatcher(
-                _gl, _meshShader, _textureCache, _wbMeshAdapter, _wbEntitySpawnAdapter, _bindlessSupport);
+                _gl, _meshShader!, _textureCache!, _wbMeshAdapter, _wbEntitySpawnAdapter, _bindlessSupport);
         }
 
         // Phase G.1 sky renderer — its own shader (sky.vert / sky.frag)
@@ -1555,7 +1559,7 @@ public sealed class GameWindow : IDisposable
             Path.Combine(shadersDir, "sky.vert"),
             Path.Combine(shadersDir, "sky.frag"));
         _skyRenderer = new AcDream.App.Rendering.Sky.SkyRenderer(
-            _gl, _dats, skyShader, _textureCache, _samplerCache);
+            _gl, _dats, skyShader, _textureCache!, _samplerCache);
 
         // Phase G.1 particle renderer — renders rain / snow / spell auras
         // spawned into the shared ParticleSystem as billboard quads.

src/AcDream.App/Rendering/Shaders/mesh_instanced.frag

@@ -1,98 +0,0 @@
-#version 430 core
-
-in vec2 vTex;
-in vec3 vWorldNormal;
-in vec3 vWorldPos;
-
-out vec4 fragColor;
-
-// One 2D texture per draw call — same binding point as mesh.frag so the
-// C# side can use the same TextureCache without a texture-array pipeline.
-uniform sampler2D uDiffuse;
-
-// Translucency kind — matches TranslucencyKind C# enum (same as mesh.frag):
-//   0 = Opaque     — depth write+test, no blend; shader never discards
-//   1 = ClipMap    — alpha-key discard at 0.5 (doors, windows, vegetation)
-//   2 = AlphaBlend — GL blending handles compositing; do NOT discard
-//   3 = Additive   — GL additive blending; do NOT discard
-//   4 = InvAlpha   — GL inverted-alpha blending; do NOT discard
-uniform int uTranslucencyKind;
-
-// Phase G.1+G.2: shared scene-lighting UBO (see mesh.frag for layout docs).
-struct Light {
-    vec4 posAndKind;
-    vec4 dirAndRange;
-    vec4 colorAndIntensity;
-    vec4 coneAngleEtc;
-};
-layout(std140, binding = 1) uniform SceneLighting {
-    Light uLights[8];
-    vec4  uCellAmbient;
-    vec4  uFogParams;
-    vec4  uFogColor;
-    vec4  uCameraAndTime;
-};
-
-vec3 accumulateLights(vec3 N, vec3 worldPos) {
-    vec3 lit = uCellAmbient.xyz;
-    int activeLights = int(uCellAmbient.w);
-    for (int i = 0; i < 8; ++i) {
-        if (i >= activeLights) break;
-
-        int kind = int(uLights[i].posAndKind.w);
-        vec3 Lcol = uLights[i].colorAndIntensity.xyz * uLights[i].colorAndIntensity.w;
-
-        if (kind == 0) {
-            vec3 Ldir = -uLights[i].dirAndRange.xyz;
-            float ndl = max(0.0, dot(N, Ldir));
-            lit += Lcol * ndl;
-        } else {
-            vec3 toL = uLights[i].posAndKind.xyz - worldPos;
-            float d  = length(toL);
-            float range = uLights[i].dirAndRange.w;
-            if (d < range && range > 1e-3) {
-                vec3 Ldir = toL / max(d, 1e-4);
-                float ndl = max(0.0, dot(N, Ldir));
-                float atten = 1.0;
-                if (kind == 2) {
-                    float cos_edge = cos(uLights[i].coneAngleEtc.x * 0.5);
-                    float cos_l    = dot(-Ldir, uLights[i].dirAndRange.xyz);
-                    atten *= (cos_l > cos_edge) ? 1.0 : 0.0;
-                }
-                lit += Lcol * ndl * atten;
-            }
-        }
-    }
-    return lit;
-}
-
-vec3 applyFog(vec3 lit, vec3 worldPos) {
-    int mode = int(uFogParams.w);
-    if (mode == 0) return lit;
-    float d = length(worldPos - uCameraAndTime.xyz);
-    float fogStart = uFogParams.x;
-    float fogEnd   = uFogParams.y;
-    float span = max(1e-3, fogEnd - fogStart);
-    float fog = clamp((d - fogStart) / span, 0.0, 1.0);
-    return mix(lit, uFogColor.xyz, fog);
-}
-
-void main() {
-    vec4 color = texture(uDiffuse, vTex);
-
-    // Alpha cutout only for clip-map surfaces (doors, windows, vegetation).
-    if (uTranslucencyKind == 1 && color.a < 0.5) discard;
-
-    vec3 N = normalize(vWorldNormal);
-    vec3 lit = accumulateLights(N, vWorldPos);
-
-    // Lightning flash — additive scene bump.
-    lit += uFogParams.z * vec3(0.6, 0.6, 0.75);
-
-    // Retail clamp per-channel to 1.0 (r13 §13.1).
-    lit = min(lit, vec3(1.0));
-
-    vec3 rgb = color.rgb * lit;
-    rgb = applyFog(rgb, vWorldPos);
-    fragColor = vec4(rgb, color.a);
-}

src/AcDream.App/Rendering/Shaders/mesh_instanced.vert

@@ -1,35 +0,0 @@
-#version 430 core
-
-// Per-vertex attributes
-layout(location = 0) in vec3 aPosition;
-layout(location = 1) in vec3 aNormal;
-layout(location = 2) in vec2 aTexCoord;
-
-// Per-instance model matrix, split across four vec4 attribute slots.
-// A mat4 consumes 4 consecutive attribute locations, so locations 3-6 are
-// all occupied by this single logical matrix.  The C# side must call
-// VertexAttribPointer four times (one per row) and VertexAttribDivisor(loc, 1)
-// on each of the four slots.
-layout(location = 3) in vec4 aInstanceRow0;
-layout(location = 4) in vec4 aInstanceRow1;
-layout(location = 5) in vec4 aInstanceRow2;
-layout(location = 6) in vec4 aInstanceRow3;
-
-uniform mat4 uViewProjection;
-
-out vec2 vTex;
-out vec3 vWorldNormal;
-out vec3 vWorldPos;
-
-void main() {
-    // Reconstruct the per-instance model matrix from its four row vectors.
-    mat4 model = mat4(aInstanceRow0, aInstanceRow1, aInstanceRow2, aInstanceRow3);
-
-    vec4 worldPos = model * vec4(aPosition, 1.0);
-    gl_Position = uViewProjection * worldPos;
-
-    vWorldPos = worldPos.xyz;
-    // Transform normal into world space.
-    vWorldNormal = normalize(mat3(model) * aNormal);
-    vTex = aTexCoord;
-}