【SkiaSharp绘图05】SKPaint详解（三）之ImageFilter(颜色、组合、膨胀、移位、光照、反射、阴影、腐蚀、变换)

文章目录

ImageFilter
- CreateColorFilter 颜色滤镜
- CreateCompose 滤镜组合
- CreateDilate 膨胀滤镜
- CreateDisplacementMapEffect 移位映射
- CreateDistantLitDiffuse 光照
- CreateDistantLitSpecular 反射光照
- CreateDropShadow阴影效果
- CreateDropShadowOnly 只阴影效果
- CreateErode腐蚀效果
- CreateMatrix变换矩阵

ImageFilter

CreateColorFilter 颜色滤镜

public static SkiaSharp.SKImageFilter CreateColorFilter (SkiaSharp.SKColorFilter cf, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

SKImageFilter.CreateColorFilter 的主要作用是根据指定的颜色滤镜，对图像进行颜色调整。它的意义在于能够灵活地对图像进行颜色处理，提供了强大的工具来实现各种颜色效果。常见的颜色滤镜包括灰度滤镜、色相/饱和度/亮度调整滤镜等。

var canvas = e.Surface.Canvas;
canvas.Clear(SKColors.White);

if (skBmp == null) skBmp = SKBitmap.Decode(@"Images\AIWoman.png");

// 创建一个灰度颜色滤镜
var colorFilter = SKColorFilter.CreateColorMatrix(new float[]
{
    0.299f, 0.587f, 0.114f, 0, 0,
    0.299f, 0.587f, 0.114f, 0, 0,
    0.299f, 0.587f, 0.114f, 0, 0,
    0, 0, 0, 1, 0
});
using (var colorFilterImageFilter = SKImageFilter.CreateColorFilter(colorFilter))
using (var paint = new SKPaint())
{
    paint.FilterQuality = SKFilterQuality.High;
    canvas.DrawBitmap(skBmp, new SKRect(10, 10, 400, 400), paint);//原图

    paint.ImageFilter = colorFilterImageFilter;
    canvas.DrawBitmap(skBmp, new SKRect(410, 10, 800, 400), paint);//灰色滤镜
}

创建一个灰度滤镜，将图像转为灰度图。
CreateColorFilter

CreateCompose 滤镜组合

public static SkiaSharp.SKImageFilter CreateCompose (SkiaSharp.SKImageFilter outer, SkiaSharp.SKImageFilter inner);

滤镜组合，将应用inner(第二个)滤镜，再应用outer(第一个)滤镜。

CreateDilate 膨胀滤镜

public static SkiaSharp.SKImageFilter CreateDilate (int radiusX, int radiusY, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

SKImageFilter.CreateDilate 是 SkiaSharp 中用于创建膨胀滤镜的方法。膨胀滤镜是一种形态学滤波器，通过扩展图像中亮（或白）区域的边缘，可以增强或扩大这些区域。这在图像处理和计算机视觉中具有多种用途，如增强特定特征、减少噪声等。

CreateDisplacementMapEffect 移位映射

public static SkiaSharp.SKImageFilter CreateDisplacementMapEffect (SkiaSharp.SKColorChannel xChannelSelector, SkiaSharp.SKColorChannel yChannelSelector, float scale, SkiaSharp.SKImageFilter displacement, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

SKImageFilter.CreateDisplacementMapEffect 是 SkiaSharp 中用于创建位移映射效果的方法。位移映射是一种高级图像处理技术，通过使用一个位移图（displacement map）来偏移目标图像中的像素位置，从而产生扭曲、波纹或其他变形效果。

作用与意义

位移映射效果的主要作用和意义包括：

图像扭曲：可以用来创建各种图像扭曲效果，如波纹、水流、热空气导致的扭曲等。
变形效果：可以实现复杂的变形效果，通过调整位移图可以实现不同的视觉效果。
动态效果：在动画中，可以用位移映射来创建动态变形效果，使得图像呈现出更加生动的视觉效果。

[System.ComponentModel.Description("SKPaint.ImageFilter的CreateDilate/CreateDisplacementMapEffect/CreateCompose")]
public void OnPaintSurface05_02(object sender, SkiaSharp.Views.Desktop.SKPaintGLSurfaceEventArgs e)
{
    var canvas = e.Surface.Canvas;
    canvas.Clear(SKColors.White);

    if (skBmp == null) skBmp = SKBitmap.Decode(@"Images\AIWoman.png");

    using (var filter = SKImageFilter.CreateDilate(3F, 3F))
    using (var paint = new SKPaint())
    {
        paint.FilterQuality = SKFilterQuality.High;
        canvas.DrawBitmap(skBmp, new SKRect(10, 10, 400, 400), paint);//原图

        paint.ImageFilter = filter;
        canvas.DrawBitmap(skBmp, new SKRect(410, 10, 800, 400), paint);//

        // 创建位移映射效果滤镜
        using (var bmpFilter = SKImageFilter.CreateImage(SKImage.FromBitmap(skBmp)))
        using (var displacementMapEffect = SKImageFilter.CreateDisplacementMapEffect(
            SKColorChannel.R, // 使用红色通道作为水平位移
            SKColorChannel.G, // 使用绿色通道作为垂直位移
            20.0f, // 缩放系数
            bmpFilter))
        {
            paint.ImageFilter = displacementMapEffect;
            canvas.DrawBitmap(skBmp, new SKRect(10, 410, 400, 800), paint);//

            using(var composeFilter=SKImageFilter.CreateCompose(filter, displacementMapEffect))
            {
                paint.ImageFilter = composeFilter;
                canvas.DrawBitmap(skBmp, new SKRect(410, 410, 800, 800), paint);//
            }
        }

        paint.ImageFilter = null;
        paint.Color = SKColors.Red;
        paint.TextSize = 24;
        paint.Typeface = SKTypeface.FromFamilyName("宋体");
        canvas.DrawText($"原图", 20, 200, paint);
        canvas.DrawText($"CreateDilate", 420, 200, paint);
        canvas.DrawText($"CreateDisplacementMapEffect", 20, 600, paint);
        canvas.DrawText($"CreateCompose", 420, 600, paint);
    }
}

示例膨胀、移位映射效果、组合滤镜。
ImageFilter

CreateDistantLitDiffuse 光照

public static SkiaSharp.SKImageFilter CreateDistantLitDiffuse (SkiaSharp.SKPoint3 direction, SkiaSharp.SKColor lightColor, float surfaceScale, float kd, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

SKImageFilter.CreateDistantLitDiffuse 用于创建一种特定光照效果的滤镜方法。它模拟的是远距离光源照射在图像上的漫反射效果。这种效果可以用来模拟三维物体在光照下的阴影和高光，从而增加图像的立体感和真实感。

** 作用与意义**

增加立体感：通过模拟光源的照射，图像可以呈现出类似于三维物体的效果，增加深度感。
增强真实感：光照效果可以使图像看起来更真实，因为现实世界中的物体都是受到光源影响的。
图像处理与特效：可以在图像处理、游戏开发、UI设计等领域应用，增加视觉效果。

var canvas = e.Surface.Canvas;
var info = e.Info;

canvas.Clear();
const string TEXT = "SkiaSharp绘图";
float z = 2F;
float surfaceScale = 1F;
float lightConstant = 0.3F;
// 应用远距离漫反射照明过滤器
using (SKPaint paint = new SKPaint())
{
    paint.IsAntialias = true;

    // Size text to 90% of canvas width
    paint.TextSize = 100;
    paint.Typeface = SKTypeface.FromFamilyName("微软雅黑");

    float textWidth = paint.MeasureText(TEXT);
    paint.TextSize *= 0.9f * info.Width / textWidth;

    // Find coordinates to center text
    SKRect textBounds = new SKRect();
    paint.MeasureText(TEXT, ref textBounds);

    float xText = info.Rect.MidX - textBounds.MidX;
    float yText = info.Rect.MidY - textBounds.MidY;

    // Create distant light image filter
    paint.ImageFilter = SKImageFilter.CreateDistantLitDiffuse(
                            new SKPoint3(2, 3, z),
                            SKColors.White,
                            surfaceScale,
                            lightConstant);

    canvas.DrawText(TEXT, xText, yText, paint);
}

CreateDistantLitDiffuse

CreateDistantLitSpecular 反射光照

public static SkiaSharp.SKImageFilter CreateDistantLitSpecular (SkiaSharp.SKPoint3 direction, SkiaSharp.SKColor lightColor, float surfaceScale, float ks, float shininess, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

创建应用远距离镜面反射照明的图像滤镜。
SKImageFilter.CreateDistantLitSpecular 用于创建一种特定光照效果的滤镜方法。它模拟的是远距离光源照射在图像上的镜面反射（高光）效果。这种效果可以用来模拟物体在光照下产生的镜面高光，从而增加图像的真实感和立体感。

作用与意义

增加真实感和立体感：通过模拟光源的镜面反射效果，图像可以看起来更加真实和立体。
突出物体表面的细节：镜面反射可以突出物体表面的光滑和凹凸不平。
图像处理与特效：可以在图像处理、游戏开发、UI设计等领域应用，增加视觉效果。

var canvas = e.Surface.Canvas;
var info = e.Info;

canvas.Clear();
const string TEXT = "SkiaSharp绘图";
float z = 2F;
float surfaceScale = 1F;
float shininess = 0.3F;
float ks = 0.8f; 
using (SKPaint paint = new SKPaint())
{
    paint.IsAntialias = true;

    // Size text to 90% of canvas width
    paint.TextSize = 100;
    paint.Typeface = SKTypeface.FromFamilyName("微软雅黑");

    float textWidth = paint.MeasureText(TEXT);
    paint.TextSize *= 0.9f * info.Width / textWidth;

    // Find coordinates to center text
    SKRect textBounds = new SKRect();
    paint.MeasureText(TEXT, ref textBounds);

    float xText = info.Rect.MidX - textBounds.MidX;
    float yText = info.Rect.MidY - textBounds.MidY;


    paint.ImageFilter = SKImageFilter.CreateDistantLitSpecular(
                            new SKPoint3(2, 3, z),
                            SKColors.White,
                            surfaceScale,
                            ks,
                            shininess);

    canvas.DrawText(TEXT, xText, yText, paint);
}

CreateDistantLitSpecular

CreateDropShadow阴影效果

public static SkiaSharp.SKImageFilter CreateDropShadow (float dx, float dy, float sigmaX, float sigmaY, SkiaSharp.SKColor color, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

创建阴影效果

var canvas = e.Surface.Canvas;
var info = e.Info;

canvas.Clear(SKColors.White);
const string TEXT = "SkiaSharp绘图";

using (SKPaint paint = new SKPaint())
{
    paint.IsAntialias = true;

    // Size text to 90% of canvas width
    paint.TextSize = 100;
    paint.Typeface = SKTypeface.FromFamilyName("微软雅黑");

    float textWidth = paint.MeasureText(TEXT);
    paint.TextSize *= 0.9f * info.Width / textWidth;

    // Find coordinates to center text
    SKRect textBounds = new SKRect();
    paint.MeasureText(TEXT, ref textBounds);

    float xText = info.Rect.MidX - textBounds.MidX;
    float yText = info.Rect.MidY - textBounds.MidY;

    // 创建阴影的颜色
    SKColor shadowColor = new SKColor(0, 0, 0, 128); // 半透明的黑色阴影

    paint.ImageFilter = SKImageFilter.CreateDropShadow(6, 10, 2, 2, shadowColor);

    canvas.DrawText(TEXT, xText, yText, paint);

    paint.ImageFilter = SKImageFilter.CreateDropShadowOnly(6, 10, 2, 2, shadowColor);

    canvas.DrawText(TEXT, xText, yText+100, paint);
}

CreateDropShadowOnly 只阴影效果

public static SkiaSharp.SKImageFilter CreateDropShadowOnly (float dx, float dy, float sigmaX, float sigmaY, SkiaSharp.SKColor color, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

只显示阴影效果，不显示前景。

CreateErode腐蚀效果

public static SkiaSharp.SKImageFilter CreateErode (int radiusX, int radiusY, SkiaSharp.SKImageFilter input = default, SkiaSharp.SKImageFilter.CropRect cropRect = default);

图像腐蚀
CreateErode

CreateMatrix变换矩阵

public static SkiaSharp.SKImageFilter CreateMatrix (SkiaSharp.SKMatrix matrix, SkiaSharp.SKFilterQuality quality, SkiaSharp.SKImageFilter input = default);

用于创建一个矩阵滤镜（Matrix Filter），该滤镜可以应用一个仿射变换（如旋转、缩放、平移）到图像上。这个方法允许开发者通过指定矩阵来改变图像的几何形状和位置。

var canvas = e.Surface.Canvas;
canvas.Clear(SKColors.White);

if (skBmp == null) skBmp = SKBitmap.Decode(@"Images\AIWoman.png");

var destRect = new SKRect(410, 10, 800, 400);
// 创建一个旋转45度的仿射变换矩阵，以图像中心为旋转中心
var matrix = SKMatrix.CreateRotationDegrees(45, (destRect.Left+ destRect.Right)/2F, (destRect.Top+ destRect.Bottom)/2F);
// 创建矩阵滤镜
using (var filter = SKImageFilter.CreateMatrix(matrix, SKFilterQuality.High))
using (var paint = new SKPaint())
{
    paint.FilterQuality = SKFilterQuality.High;
    canvas.DrawBitmap(skBmp, new SKRect(10, 10, 400, 400), paint);//原图

    paint.ImageFilter = filter;
    canvas.DrawBitmap(skBmp, new SKRect(410, 10, 800, 400), paint);//

    paint.ImageFilter = null;
    paint.Color = SKColors.Red;
    paint.TextSize = 24;
    paint.Typeface = SKTypeface.FromFamilyName("宋体");
    canvas.DrawText($"原图", 20, 200, paint);
    canvas.DrawText($"CreateMatrix", 420, 200, paint);
}