Add NIF previewer plugin with Linux-specific fixes

Vendored from github.com/Parapets/mo2-preview_nif and adapted for Linux:

- BSA texture resolution via MO2 virtual tree with case-insensitive
  fallback walk (Linux FS is case-sensitive; NIFs reference textures
  with arbitrary case against files on disk)
- Process-wide cached BSA candidate list, keyed by profile path,
  priority-sorted, filtering disabled mods
- Path backslash normalization before loose-file lookup
- Polygon offset on SLSF1_Decal-flagged shapes to break z-ties with
  coincident base meshes (road decals, moss overlays)
- Opaque framebuffer via glColorMask alpha lock so alpha-blended shapes
  can't bleed the dialog background through the preview area
- QMouseEvent::globalPosition().toPoint() for Qt6 compatibility

Preview dialog behavior (organizercore.cpp):
- Switch previewFile and previewFileWithAlternatives from stack-allocated
  exec() to heap + ApplicationModal + show() + WA_DeleteOnClose.
- Parent passed as nullptr so preview lifetime is decoupled from the
  stack-allocated ModInfoDialog that spawns it. Nested exec() inside
  the enclosing dialog's exec() was softlocking on close.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

1 files changed, 101 insertions, 0 deletions

diff --git a/libs/preview_nif/data/shaders/sk_effectshader.frag b/libs/preview_nif/data/shaders/sk_effectshader.frag
new file mode 100644
index 0000000..3a22388
--- /dev/null
+++ b/libs/preview_nif/data/shaders/sk_effectshader.frag
@@ -0,0 +1,101 @@
+#version 120
+
+uniform sampler2D BaseMap;
+uniform sampler2D GreyscaleMap;
+
+uniform bool doubleSided;
+
+uniform bool hasSourceTexture;
+uniform bool hasGreyscaleMap;
+uniform bool greyscaleAlpha;
+uniform bool greyscaleColor;
+
+uniform bool useFalloff;
+uniform bool vertexColors;
+uniform bool vertexAlpha;
+
+uniform bool hasWeaponBlood;
+
+uniform vec4 glowColor;
+uniform float glowMult;
+
+uniform vec2 uvScale;
+uniform vec2 uvOffset;
+
+uniform vec4 falloffParams;
+uniform float falloffDepth;
+
+varying vec2 TexCoord;
+varying vec3 LightDir;
+varying vec3 ViewDir;
+
+varying vec4 C;
+
+varying vec3 N;
+varying vec3 v;
+
+vec4 colorLookup( float x, float y ) {
+
+    return texture2D( GreyscaleMap, vec2( clamp(x, 0.0, 1.0), clamp(y, 0.0, 1.0)) );
+}
+
+void main( void )
+{
+    vec4 baseMap = texture2D( BaseMap, TexCoord.st * uvScale + uvOffset );
+
+    vec4 color;
+
+    vec3 normal = N;
+
+    // Reconstructed normal
+    //normal = normalize(cross(dFdy(v.xyz), dFdx(v.xyz)));
+
+    //if ( !doubleSided && !gl_FrontFacing ) { return; }
+
+    vec3 E = normalize(ViewDir);
+
+    float tmp2 = falloffDepth; // Unused right now
+
+    // Falloff
+    float falloff = 1.0;
+    if ( useFalloff ) {
+        float startO = min(falloffParams.z, 1.0);
+        float stopO = max(falloffParams.w, 0.0);
+
+        // TODO: When X and Y are both 0.0 or both 1.0 the effect is reversed.
+        falloff = smoothstep( falloffParams.y, falloffParams.x, abs(E.b));
+
+        falloff = mix( max(falloffParams.w, 0.0), min(falloffParams.z, 1.0), falloff );
+    }
+
+    float alphaMult = glowColor.a * glowColor.a;
+
+    color.rgb = baseMap.rgb;
+    color.a = baseMap.a;
+
+    if ( hasWeaponBlood ) {
+        color.rgb = vec3( 1.0, 0.0, 0.0 ) * baseMap.r;
+        color.a = baseMap.a * baseMap.g;
+    }
+
+    color.rgb *= C.rgb * glowColor.rgb;
+    color.a *= C.a * falloff * alphaMult;
+
+    if ( greyscaleColor ) {
+        // Only Red emissive channel is used
+        float emRGB = glowColor.r;
+
+        vec4 luG = colorLookup( baseMap.g, C.g * falloff * emRGB );
+
+        color.rgb = luG.rgb;
+    }
+
+    if ( greyscaleAlpha ) {
+        vec4 luA = colorLookup( baseMap.a, C.a * falloff * alphaMult );
+
+        color.a = luA.a;
+    }
+
+    gl_FragColor.rgb = color.rgb * glowMult;
+    gl_FragColor.a = color.a;
+}