UVs with stacked shaders

[Froyok]

I have been trying out shaderfilter-plus for a few days now (and it's great !) and I stumbled upon a behavior that I'm not sure if it's a bug or by design.

I'm trying to build generic effects that I can re-use over different sources in OBS and also to make the shaders easier to manage and maintain. So I built a first shader that applies an animated gradient by manipulating the UV coordinates. Then I added a second shader to perform another kind of gradient/UV based animation.

Current behavior: When shaders are stacked, it seems the second shader inherit the UVs from the previous one (or something alike).

Expected behavior: When shaders are stacked, the given uv variable at the entry or render() should give the same values with or without stacked shaders.

• Shaderfilter-plus version : 0.1.3
• OBS Version : 25.0.8-1
• OS : Linux, Manjaro
• GPU : AMD Radeon RX 5600 XT
• Drivers/Versions : NAVI10, DRM 3.36.0, 5.6.16-1-MANJARO, LLVM 10.0.0, Mesa 20.1.3

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The current behavior prevent the creation of effects based on multiple pass (like separable/box blurs) and make other effects difficult to build if you have to take into account previous shaders.

Demo of the behavior

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Simple Shader code to replicate that behavior:

Shader 1

float4 render(float2 uv)
{
    vec4 Result = image.Sample(builtin_texture_sampler, uv);
    float Mask = fract( uv.x + builtin_elapsed_time * 2.0 );
    Mask = abs( Mask * 2.0 - 1.0 );

    Result.rgb *= Mask;
    return Result;
}

Shader 2

float4 render(float2 uv)
{
    return vec4( uv.x, uv.y, 0.0, 1.0 );
}

[Limeth]

Hello, can you please describe the behavior that you would expect? I'm not sure I understand the issue. Preceding shaders do not let you change the UV coordinates for the following shaders. The current behavior as shown in the demo seems correct to me.

[Froyok]

After looking more closely, following up your answer, I think I made a mistake. :)

I think I got confused by the UI and the order in which shaders are applied. I thought the shaders were stacked from bottom to top (like a layer stack), while in fact it's the opposite. So the first shader to be applied is the one at the top of the list. Now that I understand that, it seems there is indeed no issues.

[Limeth]

Glad to hear that, if you run into any other problems, feel free to make another issue. :)