iOS 12上的UIImage.withTintColor的等效性如何？

Question

[从iOS 13.0+开始，UIImage class has method withTintColor。

iOS 12.4上的等效功能如何，以支持不能运行iOS 13的旧版iPhone？

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[总体目标

是绘制带有黑色或白色发光效果（深色或浅色主题）的着色图像。

这是Xamarin.Forms.Platform.iOS.PlatformEffect的一部分。

Xamarin C＃iOS

代码将着色图像覆盖的光晕绘制为位图-在iOS 13上有效：

private static UIImage ApplyGlow2( UIImage src, double radius, Xamarin.Forms.Color color,
                                   Xamarin.Forms.Color? tintColor, int outW, int outH)
{
    int glowRadius = (int)radius;
    // Increase size of the initial image.
    int marginX2 = glowRadius * 2;
    int margin = glowRadius;

    // Resize original image to display size.
    UIGraphics.BeginImageContext(new CGSize(outW, outH));
    src.Draw(new CGRect(0, 0, outW, outH));
    src = UIGraphics.GetImageFromCurrentImageContext();
    UIGraphics.EndImageContext();


    // Add margins.
    UIGraphics.BeginImageContext(new CGSize(outW + marginX2, outH + marginX2));
    CGContext context = UIGraphics.GetCurrentContext();
    CGRect drawRect = new CGRect(margin, margin, outW, outH);

    src.Draw(drawRect);

    src = UIGraphics.GetImageFromCurrentImageContext();
    UIGraphics.EndImageContext();

    // Create color overlay.
    UIGraphics.BeginImageContext(new CGSize(outW + marginX2, outH + marginX2));
    context = UIGraphics.GetCurrentContext();
    drawRect = new CGRect(0, 0, outW + marginX2, outH + marginX2);
    context.TranslateCTM(0, outH + marginX2);
    context.ScaleCTM(1.0f, -1.0f);


    context.SetBlendMode(CGBlendMode.Normal);
    context.SetFillColor(color.ToCGColor());
    context.FillRect(drawRect);

    context.SetBlendMode(CGBlendMode.DestinationIn);
    context.DrawImage(drawRect, src.CGImage);


    UIImage ret = UIGraphics.GetImageFromCurrentImageContext();
    UIGraphics.EndImageContext();

    // Create blurred image;
    // create a CIGaussianBlur filter with the input image.
    CIGaussianBlur gaussian_blur = new CIGaussianBlur()
    {
        InputImage = ret.CGImage,
        Radius = (float)radius * 0.5f,
    };
    CIImage output = gaussian_blur.OutputImage;
    CIContext context2 = CIContext.FromOptions(null);
    CGImage cgimage = context2.CreateCGImage(output, new CGRect(new CGPoint(0,0), ret.Size));
    UIImage blurredImage = UIImage.FromImage(cgimage);


    // -- Merge blur with original. --      
    UIGraphics.BeginImageContext(new CGSize(outW + marginX2, outH + marginX2));
    //CGContext context3 = UIGraphics.GetCurrentContext();

    // Blur.
    CGRect drawRect2 = new CGRect(0, 0, outW + marginX2, outH + marginX2);
    CGRect drawRect3 = new CGRect(1, 1, outW + marginX2, outH + marginX2);
    CGRect drawRect4 = new CGRect(2, 2, outW + marginX2, outH + marginX2);
    blurredImage.Draw(drawRect2);
    blurredImage.Draw(drawRect3);
    blurredImage.Draw(drawRect4);

    if (tintColor != null) {
        // Draw tinted original (over blur).
        var tintedImage = src.ApplyTintColor( tintColor.Value.ToUIColor() );
        tintedImage.Draw( drawRect2 );
    } else {
        // Draw original (over blur).
        src.Draw( drawRect2 );
    }
    ret = UIGraphics.GetImageFromCurrentImageContext();
    UIGraphics.EndImageContext();

    return ret;
}
上方与我的问题最相关的行：

// Draw tinted original (over blur).
var tintedImage = src.ApplyTintColor( tintColor.Value.ToUIColor() );
tintedImage.Draw( drawRect2 );
我尝试过的事情：

iOS 12确实具有可以在渲染到UIImageView时应用的TintColor，但是当以编程方式绘制到UIImage中时，我没有看到使用该颜色的方法：

// Apply tint color. UIImageView Control.
Control.Image = Control.Image.ImageWithRenderingMode(UIKit.UIImageRenderingMode.AlwaysTemplate);
Control.TintColor = ((TintedImage)Element).TintColor.ToUIColor();
上面的代码类似于Using Tint color on UIImageView，这是我所看到的最接近的SO帖子。

[还有其他几篇类似的文章，但是AFAIK都使用uiimageview.tintColor

，并且不添加与绘制位图有关的任何其他信息（不是视图）。

How to apply a tintColor to a UIImage?

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[如果有某种方法可以创建不属于视图层次结构的UIView，请设置其TintColor，然后将其渲染为位图，这可能是解决此问题的一种方法。但是我不知道该怎么做。这种方法的一个步骤类似于这些帖子：

• How to convert a UIView to an image。
• How to capture UIView to UIImage without loss of quality on retina display。

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我正在通过Xamarin.iOS进行编程，但是可以接受任何iOS语言的解决方案。

[从iOS 13.0+开始，UIImage类具有withTintColor的方法。如何在iOS 12.4上实现等效功能，以支持无法运行iOS 13的旧版iPhone？总体目标是绘制有色图像，并使用...

Answer 1

（（Xamarin C＃iOS）