GLTF Glass Materials Render Without Volume on Windows/OpenGL (v1.68.4)

**Description**:

I'm experiencing an issue where GLTF models with glass materials appear to render without any volume-they look flat or like dull plastic-when using Filament 1.68.4 on Windows with OpenGL as the backend.

**Platform**:

Windows
OpenGL backend
Filament version: 1.68.4

**Repro Steps:**

1. Apply graphics setting to AR's `View`, that renders GLTF model (attached below).
2. Render an AR model and feed to a texture using an image.mat material (attached below).
3. Use this texture as a parameter for another on-screen material.
4. Use [the Dragon Attenuation model](https://github.com/KhronosGroup/glTF-Sample-Models/tree/main/2.0/DragonAttenuation) for testing.
5. [The rendering pipeline uses multiple render targets in the same render loop](https://github.com/0xcode-lasagna/filament_renderer/blob/c9d0c9fb1256cd7b617ff01a19e71ef6d4b1f0d9/src/RendererApp.cpp#L457C5-L510C6).

**Expected Behavior:**

The glass material should appear volumetric, as it does in [the minimal boilerplate project](https://github.com/0xcode-lasagna/filament_renderer) (it uses the same settings, and the model renders correctly there.).


**Actual Behavior:**

The glass material looks flat, similar to dull plastic.
This effect can also be reproduced by setting `hasVolume`, `hasVolumeThicknessTexture`, and `hasDispersion `to `false `in the `filament::gltfio::MaterialKey` config.
setScreenSpaceRefractionEnabled is enabled for the view.
The same behavior occurs with both Ubershader and JIT material providers.


**Additional Info:**

GraphicsSettings

```
struct GraphicsSettings
{
// standalone View settings
filament::AntiAliasing antiAliasing = filament::AntiAliasing::FXAA;
filament::Dithering dithering = filament::Dithering::TEMPORAL;
filament::ShadowType shadowType = filament::ShadowType::PCF;
bool postProcessingEnabled = true;

// View Options (sorted)
filament::AmbientOcclusionOptions ssao = { .enabled = true };
filament::ScreenSpaceReflectionsOptions screenSpaceReflections = { .enabled = true };
filament::BloomOptions bloom = {
.strength = 1.0f,
.enabled = true,
.lensFlare = true,
.ghostThreshold = 2.f,
.haloThreshold = 2.f,
};

filament::DepthOfFieldOptions dof = { .enabled = true, .nativeResolution = true };
filament::DynamicResolutionOptions dsr = { .minScale = { 1.f, 1.f },
.maxScale = { 2.0f, 2.0f },
.sharpness = 0.9f,
.enabled = false,
.quality = filament::QualityLevel::LOW };
filament::FogOptions fog;
// # if !defined(__EMSCRIPTEN__) && !defined(__EMSCRIPTEN_PTHREADS__)
filament::MultiSampleAntiAliasingOptions msaa = { .enabled = true, .sampleCount = 4 };
// # else
// filament::MultiSampleAntiAliasingOptions msaa = { .enabled = false };
// # endif
filament::RenderQuality renderQuality;
filament::TemporalAntiAliasingOptions taa = { .enabled = true };
filament::VignetteOptions vignette = { .enabled = false };
filament::VsmShadowOptions vsmShadowOptions = { .anisotropy = 0 };
filament::GuardBandOptions guardBand;
filament::BlendMode blendMode = filament::BlendMode::TRANSLUCENT;

filament::View* Apply(filament::View* view) const;
};

// Actual graphics settings for AR model rendering
{
.postProcessingEnabled = true,
.ssao = { .enabled = false },
.screenSpaceReflections = { .enabled = false },
.bloom = {
.dirtStrength = 1.0f,
.strength = 1.0f,
.blendMode = filament::BloomOptions::BlendMode::INTERPOLATE,
.threshold = true,
.enabled = true,
.lensFlare = false,
.chromaticAberration = 0.03f,
.ghostThreshold = 0.000000002f,
.haloThreshold = 0.000000002f,
},
.dof = { .enabled = false, .nativeResolution = true },
.dsr = { .minScale = { 1.f, 1.f }, .maxScale = { 2.0f, 2.0f }, .sharpness = 0.9f, .enabled = false, .quality = filament::QualityLevel::LOW },
.fog = {},
.msaa = { .enabled = true, .sampleCount = 4 },
.renderQuality = {},
.taa = { .enabled = false },
.vignette = { .enabled = false },
.vsmShadowOptions = { .anisotropy = 0 },
.guardBand = {}
},
```

image.mat

```
material {
name : image,
parameters : [
{
type : ${FEED_SAMPLER},
name : image
}
],
requires : [
uv0
],
flipUV : true,
depthWrite : false,
colorWrite : true,
shadingModel : unlit,
variantFilter : [ directionalLighting, dynamicLighting, shadowReceiver, skinning, fog, vsm ],
culling: none,
depthCulling : false
}

fragment {
#if USE_SAMPLER_EXTERNAL
vec3 sRGB_to_linear(highp vec3 color) {
return vec3(
color.r <= 0.04045 ? color.r / 12.92 : pow((color.r + 0.055) / 1.055, 2.4),
color.g <= 0.04045 ? color.g / 12.92 : pow((color.g + 0.055) / 1.055, 2.4),
color.b <= 0.04045 ? color.b / 12.92 : pow((color.b + 0.055) / 1.055, 2.4)
);
//return vec3(pow(color.r, 2.2), pow(color.g, 2.2), pow(color.b, 2.2));
//return color;
}
#endif

vec3 imageColor(highp vec2 uv) {
uv = vec2(uv.s, 1.0 - uv.t);
// We need to convert extneral texture to linear space
// (in case of internal texture - we do it with hardware automatically based RGB8_A8 format)
#if USE_SAMPLER_EXTERNAL
return sRGB_to_linear(texture(materialParams_image, uv).rgb);
#else
return texture(materialParams_image, uv).rgb;
#endif
}

void material(inout MaterialInputs material) {
prepareMaterial(material);
highp vec2 imageUV = getUV0();
if (imageUV.x > 0.0 && imageUV.y > 0.0 && imageUV.x < 1.0 && imageUV.y < 1.0 ) {
material.baseColor.rgb = imageColor(imageUV);
material.baseColor.a = 1.0;
}else{
material.baseColor = vec4(0.0, 0.0, 0.0, 1.0);
}
}
}

```

I'm happy to provide code snippets or further details if needed.

**Question:**

Is there something I'm missing in the pipeline or material configuration that could cause this? Any hints or suggestions would be greatly appreciated!