WPF中的3種顏色AngleGradient

Question

我正在嘗試在WPF中實現簡單的3色角度漸變。 最好的情況是您得到了僅XAML的答案，但是我很確定這是不可能的。

這個問題和答案（ 在WPF中為AngleGradient ）是我想要的一半。 我嘗試使用該代碼，但顯然數學沒有正確。

我的問題是：我該如何正確執行上述問題，但要使用3種顏色以及3和1之間的漸變（在上面的問題中，漸變是從藍色到白色，但又直接回到藍色）之后，我也想要從白色到藍色的反向漸變。

將其視為具有完美水平底面的等邊三角形。 例如，我要在上角處使用紅色，在左下角處使用綠色，在右下角處使用藍色，並且在兩者之間具有理想的角度輻射。

我不介意像其他線程建議的答案那樣編譯成.ps ：）

非常感謝 ！

Answer 1

我認為其他線程可以很好地解釋您需要做什么。 您將需要將所有三種顏色傳遞給着色器，然后對每個像素進行數學運算以獲得所需的顏色。

以與其他答案相同的方式獲取當前像素的0-1角。 然后以那個角度在適當的顏色之間徘徊。

着色器

sampler2D inputSampler : register(S0);
float2 center : register(C0);
float4 firstColor : register(C1);
float4 secondColor : register(C2);
float4 thirdColor : register(C3);

float4 main(float2 uv : TEXCOORD) : COLOR
{
    // Put the three colors into an array.
    float4 colors[3] = { firstColor, secondColor, thirdColor };

    // Figure out where this pixel is in relation to the center point
    float2 pos = center - uv;

    // Compute the angle of this pixel relative to the center (in radians),
    // then divide by 2 pi to normalize the angle into a 0 to 1 range.
    // We are flipping the Y here so that 0 is at the top (instead of the bottom) and we
    // rotate clockwise. Could also flip X if we want to rotate counter-clockwise.
    float value = (atan2(pos.x, -pos.y) + 3.141596) / (2.0 * 3.141596);

    // Scale the angle based on the size of our array and determine which indices
    // we are currently between, wrapping around to 0 at the end.
    float scaledValue = value * 3;
    float4 prevColor = colors[(int)scaledValue];
    float4 nextColor = colors[((int)scaledValue + 1) % 3];

    // Figure out how far between the two colors we are
    float lerpValue = scaledValue - (float)((int)scaledValue);

    // Get the alpha of the incoming pixel from the sampler.
    float alpha = tex2D(inputSampler, uv).a;

    // Lerp between the colors. Multiply each color by its own alpha and the result by the
    // incoming alpha becuse WPF expects shaders to return premultiplied alpha pixel values.
    return float4(
        lerp(prevColor.rgb * prevColor.a, nextColor.rgb * nextColor.a, lerpValue) * alpha,
        lerp(prevColor.a, nextColor.a, lerpValue) * alpha);
}

影響

class AngleGradientEffect : ShaderEffect
{
    public Brush Input
    {
        get { return (Brush)GetValue(InputProperty); }
        set { SetValue(InputProperty, value); }
    }
    public static readonly DependencyProperty InputProperty = RegisterPixelShaderSamplerProperty("Input", typeof(AngleGradientEffect), 0);

    public Point Center
    {
        get { return (Point)GetValue(CenterProperty); }
        set { SetValue(CenterProperty, value); }
    }
    public static readonly DependencyProperty CenterProperty = DependencyProperty.Register("Center", typeof(Point), typeof(AngleGradientEffect),
        new PropertyMetadata(new Point(0.5, 0.5), PixelShaderConstantCallback(0)));

    public Color FirstColor
    {
        get { return (Color)GetValue(FirstColorProperty); }
        set { SetValue(FirstColorProperty, value); }
    }
    public static readonly DependencyProperty FirstColorProperty = DependencyProperty.Register("FirstColor", typeof(Color), typeof(AngleGradientEffect),
        new PropertyMetadata(Color.FromRgb(255, 0, 0), PixelShaderConstantCallback(1)));

    public Color SecondColor
    {
        get { return (Color)GetValue(SecondColorProperty); }
        set { SetValue(SecondColorProperty, value); }
    }
    public static readonly DependencyProperty SecondColorProperty = DependencyProperty.Register("SecondColor", typeof(Color), typeof(AngleGradientEffect),
        new PropertyMetadata(Color.FromRgb(0, 255, 0), PixelShaderConstantCallback(2)));

    public Color ThirdColor
    {
        get { return (Color)GetValue(ThirdColorProperty); }
        set { SetValue(ThirdColorProperty, value); }
    }
    public static readonly DependencyProperty ThirdColorProperty = DependencyProperty.Register("ThirdColor", typeof(Color), typeof(AngleGradientEffect),
        new PropertyMetadata(Color.FromRgb(0, 0, 255), PixelShaderConstantCallback(3)));

    public AngleGradientEffect()
    {
        // ResourceHelper is my own utility that formats URIs for me. The returned URI
        // string will be something like /AssemblyName;component/Effects/AngleGradient.ps
        PixelShader = new PixelShader() { UriSource = ResourceHelper.GetResourceUri("Effects/AngleGradient.ps", relative: true)};

        UpdateShaderValue(InputProperty);
        UpdateShaderValue(CenterProperty);
        UpdateShaderValue(FirstColorProperty);
        UpdateShaderValue(SecondColorProperty);
        UpdateShaderValue(ThirdColorProperty);
    }
}

用法

<Ellipse
    Width="200"
    Height="200"
    Fill="White">
    <Ellipse.Effect>
        <effects:AngleGradientEffect
            FirstColor="Red"
            SecondColor="Lime"
            ThirdColor="Blue" />
    </Ellipse.Effect>
</Ellipse>

請記住，在某些情況下，在RGB空間中的不同色調之間進行插值會提供一些難看的結果。 如果您希望這樣做，則可能要考慮轉換為HSV並插入色相。