Setting pixel shader uniform variable

Question

Dummy question, I guess. I have a custom shader that looks like this:

sampler2D InputTexture;

float parameter1, parameter2 etc

float4 main(float2 uv : TEXCOORD) : COLOR
{
    float4 result = blah-blah-blah some calculations using parameter1, parameter2 etc.

    return result;
}

I'm trying to use it via wrapper that looks like this:

class MyShaderEffect : ShaderEffect
{
    private PixelShader _pixelShader = new PixelShader();
    public readonly DependencyProperty InputProperty = ShaderEffect.RegisterPixelShaderSamplerProperty("Input", typeof(MyShaderEffect), 0);

    public MyShaderEffect()
    {
        _pixelShader.UriSource = new Uri("MyShader.ps", UriKind.Relative);
        this.PixelShader = _pixelShader;
        this.UpdateShaderValue(InputProperty);
    }

    public Brush Input
    {
        get { return (Brush)this.GetValue(InputProperty); }
        set { this.SetValue(InputProperty, value); }
    }
}

So, my question is: how do I set those shader parameters from C# program?

Eli Arbel Eli Arbel · Accepted Answer · 2016-07-19T15:00:50

It's right there in the documentation of the ShaderEffect class. You need to create dependency properties for every parameter. For example:

class MyShaderEffect
{
    public MyShaderEffect()
    {
        PixelShader = _pixelShader;

        UpdateShaderValue(InputProperty);
        UpdateShaderValue(ThresholdProperty);
    }

    public double Threshold
    {
        get { return (double)GetValue(ThresholdProperty); }
        set { SetValue(ThresholdProperty, value); }
    }

    public static readonly DependencyProperty ThresholdProperty =
        DependencyProperty.Register("Threshold", typeof(double), typeof(MyShaderEffect),
                new UIPropertyMetadata(0.5, PixelShaderConstantCallback(0)));
}

The 0 in PixelShaderConstantCallback refers to the register you use in HLSL:

float threshold : register(c0);

This way WPF knows to update the shader when the property changes. It's also important to call UpdateShaderValue in the constructor to initially pass the value.

Setting pixel shader uniform variable

1 Answers