When using "URP Sampler Buffer" in "FullScreen ShaderGraph," the sampling result will be black when the UV value is set to 1

[madnesslabo]

I was making a shader for a vortex effect on the screen.
This is the correct result.

It seems that when the UV value input to the “URP Sampler Buffer” node reaches the upper limit of 1, sampling fails and the image is drawn black.
There are black area on the top right and bottom right.

The current workaround for this is to clamp the UV and set the upper limit to less than 1, such as 0.9999.

Alternatively, I was able to solve the problem by using SamplerTexure2D instead of the URP Sampler Buffer.

The shader code generated by the “URP Sampler Buffer” is as follows.

float4 Unity_Universal_SampleBuffer_BlitSource_float(float2 uv)
{
     uint2 pixelCoords = uint2(uv * _ScreenSize.xy);
     return LOAD_TEXTURE2D_X_LOD(_BlitTexture, pixelCoords, 0);
}

When calculating pixel coordinates from uvs and texture size, I think you need to subtract the texture size by 1.

uv * (_ScreenSize.xy-1)

Alternatively, I think it would be simpler to use the uv value as is, without converting uv to pixelCoords.
A similar problem has been pointed out in this thread.

Full Screen Shaders in URP?

Hi. So I’m still just very bad at shaders. Long story short, I need a shader for a shockwave effect over top the entire scene. i’m trying to follow this tutorial here, which led to this video here, which pointed to this link. I tried to follow along as best as I could but I feel like the information is either way over my head, or outdated or something. I can’t seem to get a full screen shader to work following these instructions. I think my main problem is after I’m supposed to add the blit. Whe…

It would also be better if users could set a “Samper State” for the “URP Sampler Buffer”.

[Apoorva_Joshi]

Hey, as you observed, you’re getting a black value when you’re sampling outside the original texture, i.e. when your U or your V coordinate is outside the range [0, 1]. This is standard GPU behavior. The most proper fix for your effect is probably to never sample outside of screen bounds, i.e. you should probably do a small zoom in while doing the wobble effect, to make sure you never sample off-screen. So this is not a bug.

However, your sampler state clamp looks like the next best thing. You can read more about sampler state addressing modes here: Texture addressing modes - UWP applications

[madnesslabo]

Thank you for your reply.

1 is within the range [0, 1]. Why would that cause an issue?
When I added a Clamp node,
Clamp(0,1) had the same problem.
Clamp(0,0.9999) gave me the expected results.

I checked the generated shader code and it looked like this.

float4 Unity_Universal_SampleBuffer_BlitSource_float(float2 uv)
{
    uint2 pixelCoords = uint2(uv * _ScreenSize.xy);
    return LOAD_TEXTURE2D_X_LOD(_BlitTexture, pixelCoords, 0);
}

Is this calculation method correct?

Why does SamplerTexure2D and URP Sampler Buffer work differently?