BlazorGL 'Shader Compilation Failed' runtime exception using fwidth function

[dtaylorus]

This shader works on multiple MonoGame platforms (iOS, Android, DesktopGL) but fails at runtime on the KNI BlazorGL platform.

Can you tell me how I can fix it? Or somehow debug the runtime compilation?

#if OPENGL
	#define SV_POSITION POSITION
	#define VS_SHADERMODEL vs_3_0
	#define PS_SHADERMODEL ps_3_0
#else
	#define VS_SHADERMODEL vs_4_0_level_9_3
	#define PS_SHADERMODEL ps_4_0_level_9_3
#endif

float2 TextureSize;
float PxRange;
float Thickness;

sampler SpriteTextureSampler : register(s0);

struct VertexShaderOutput
{
	float4 Position : SV_POSITION;
	float4 Color : COLOR0;
	float2 TexCoord : TEXCOORD0;
};

float Median(float a, float b, float c)
{	
	return max(min(a, b), min(max(a, b), c));
}

float LinearStep(float a, float b, float x) {
	return clamp((x - a) / (b - a), 0.0, 1.0);
}

float4 SamplePS(VertexShaderOutput input) : COLOR
{
	float2 p = input.TexCoord;
	float pxSize = min(0.5 / PxRange * (fwidth(p.x) * TextureSize.x + fwidth(p.y) * TextureSize.y), 0.25);

	float3 samp = tex2D(SpriteTextureSampler, p).rgb;

	float sigDist = 2.0f * Median(samp.r, samp.g, samp.b) - 1.0f + Thickness;

	float opacity = LinearStep(-pxSize, pxSize, sigDist);

	return input.Color * opacity;
}

technique SmoothText
{
	pass P0
	{
		PixelShader = compile PS_SHADERMODEL SamplePS();		
	}
};

[dtaylorus]

After chasing down some red herrings, I think the problem is actually the fwidth function.

[dtaylorus]

I remember this being a problem in older versions of MonoGame. The GL_OES_standard_derivatives extension needs to be enabled for the fwidth function.

[dtaylorus]

I'm unable to find a solution for using fwidth in a shader in a BlazorGL project. Help is appreciated!

[dtaylorus]

Created issue #1816