在 PostScript 中使用渐变 | .NET

在 PS 文档中添加渐变

本文将探讨如何在 PS 文档中使用渐变。

渐变是指颜色从一种颜色平滑过渡到另一种颜色，用于使绘制的图像更加逼真。 由于渐变是一种绘画，因此在 .NET 中，它被实现为 System.Drawing.Brush 的子类。实际上，.NET 平台有两种这样的画笔：

• System.Drawing.LinearGradientBrush
• System.Drawing.PathGradientBrush

为了在 PsDocument 中设置绘画或描边，我们必须分别将 System.Drawing.Brush 类的对象（用于绘画）和 System.Drawing.Pen 类的对象（用于描边）分别传递给相应的方法。 Aspose.Page for .NET 库处理 .NET 平台提供的所有 System.Drawing.Brush 子类。这些子类包括 System.Drawing.SolidBrush、System.Drawing.TextureBrush、System.Drawing.LinearGradientBrush、System.Drawing.PathGradientBrush 和 System.Drawing.HatchBrush。System.Drawing.Pen 类由于已封装，因此无法扩展，但它包含 System.Drawing.Brush 属性，因此 Aspose.Page for .NET 库也可以使用一整套画笔来绘制线条、勾勒形状和文本的轮廓。

为了在 Aspose.Page for .NET 库中使用渐变色绘制图形对象，需要创建 System.Drawing.LinearGradientBrush 或 System.Drawing.PathGradientBrush，并将其传递给 SetPaint() 或 FillText() 或 FillAndStrokeText() 方法（这些方法接受 System.Drawing.Brush 作为参数）。

为了在 Aspose.Page for .NET 库中使用渐变色勾勒图形对象轮廓，需要创建 System.Drawing.LinearGradientBrush 或 System.Drawing.PathGradientBrush，然后使用此画笔创建 System.Drawing.Pen，最后将其传递给 SetStroke() 或 OutlineText() 或 FillAndStrokeText() 方法（这些方法接受 System.Drawing.Pen 作为参数）。

在下面的示例中，我们演示了如何填充形状和文本，并使用渐变勾勒文本轮廓。

在新的 PS 文档中使用渐变绘制图形对象的算法包括以下步骤：

1. 为生成的 PS 文件创建输出流。
2. 创建 PsSaveOptions。
3. 使用已创建的输出流和保存选项创建 PsDocument。
4. 根据要填充或勾勒轮廓的对象，创建必要的图形路径或字体。
5. 根据所需的渐变形式，创建 System.Drawing.LinearGradientBrush 或 System.Drawing.PathGradientBrush 对象。
6. 为该画笔设置必要的变换。
7. 将渐变画笔设置为 PsDocument 中的当前画笔。
8. 使用当前画笔填充图形路径或填充文本。如果我们使用其中一种接受 System.Drawing.Brush 作为参数的文本填充方法，则可以忽略上一步。
9. 关闭页面。
10. 保存文档。

如果我们需要使用渐变来描边（勾勒轮廓）图形对象，而不是最后四步，则需要执行以下操作：

8. 创建带有渐变画笔的 System.Drawing.Pen 对象。

9. 将此画笔设置为 PsDocument 中的当前描边。

10. 使用当前描边勾勒图形路径或勾勒文本轮廓。如果我们使用其中一种接受 System.Drawing.Pen 作为参数的文本勾勒轮廓方法，则可以忽略上一步。

11. 关闭页面。

12. 保存文档。
    

我们提供了 5 个代码片段，演示了不同渐变的用法。

在此代码片段中，我们用两种颜色创建了水平线性渐变，并使用该渐变填充了矩形、填充了文本，还勾勒出了文本的轮廓。

//Create an output stream for PostScript document
using (Stream outPsStream = new FileStream(dataDir + "HorizontalGradient_outPS.ps", FileMode.Create))
{
    //Create save options with A4 size
    PsSaveOptions options = new PsSaveOptions();

    // Create new 1-paged PS Document
    PsDocument document = new PsDocument(outPsStream, options, false);

    float offsetX = 200;
    float offsetY = 100;
    float width = 200;
    float height = 100;

    //Create a graphics path from the first rectangle
    GraphicsPath path = new GraphicsPath();
    path.AddRectangle(new RectangleF(offsetX, offsetY, width, height));

    //Create linear gradient brush with the rectangle as bounds, start and end colors
    LinearGradientBrush brush = new LinearGradientBrush(new RectangleF(0, 0, width, height), Color.FromArgb(150, 0, 0, 0),
        Color.FromArgb(50, 40, 128, 70), 0f);
    //Create a transform for the brush. X and Y scale component must be equal to the width and the height of the rectangle respectively.
    //Translation components are offsets of the rectangle
    Matrix brushTransform = new Matrix(width, 0, 0, height, offsetX, offsetY);
    //Set  the transform
    brush.Transform = brushTransform;

    //Set the paint
    document.SetPaint(brush);

    //Fill the rectangle
    document.Fill(path);

    //Fill the text with the gradient
    Font font = new Font("Arial", 96, FontStyle.Bold);
    document.FillAndStrokeText("ABC", font, 200, 300, brush, new Pen(new SolidBrush(Color.Black), 2));

		//Set current stroke
		document.SetStroke(brush, 5);
    //Outline text with the gradient
    document.OutlineText("ABC", font, 200, 400);

    //Close current page
    document.ClosePage();

    //Save the document
    document.Save();
}

对于 Linux、MacOS 和其他非 Windows 操作系统，我们建议使用我们的 Aspose.Page.Drawing Nuget 包。它使用 Aspose.Drawing 后端，而非 System.Drawing 系统库。

因此，请导入 Aspose.Page.Drawing 命名空间，而不是 System.Drawing 命名空间。在以上及以下代码片段中，将使用 Aspose.Page.Drawing.RectangleF 代替 System.Drawing.RectangleF，使用 Aspose.Page.Drawing.Drawing2D.GraphicsPath 代替 System.Drawing.Drawing2D.GraphicsPath，等等。我们在 GitHub 上的代码示例包含所有必要的替换。

运行此代码的结果如下：

在此代码片段中，我们用 5 种颜色创建了一个垂直线性渐变，并用该渐变填充了一个矩形。

//Create an output stream for PostScript document
using (Stream outPsStream = new FileStream(dataDir + "VerticalGradient_outPS.ps", FileMode.Create))
{
    //Create save options with A4 size
    PsSaveOptions options = new PsSaveOptions();

    // Create new 1-paged PS Document
    PsDocument document = new PsDocument(outPsStream, options, false);

    float offsetX = 200;
    float offsetY = 100;
    float width = 200;
    float height = 100;

    //Create graphics path from the first rectangle
    GraphicsPath path = new GraphicsPath();
    path.AddRectangle(new RectangleF(offsetX, offsetY, width, height));

    //Create an array of interpolation colors
    Color[] colors = { Color.Red, Color.Green, Color.Blue, Color.Orange, Color.DarkOliveGreen };
    float[] positions = { 0.0f, 0.1873f, 0.492f, 0.734f, 1.0f };
    ColorBlend colorBlend = new ColorBlend();
    colorBlend.Colors = colors;
    colorBlend.Positions = positions;

    //Create linear gradient brush with the rectangle as bounds, start and end colors
    LinearGradientBrush brush = new LinearGradientBrush(new RectangleF(0, 0, width, height), Color.Beige, Color.DodgerBlue, 0f);
    //Set interpolation colors
    brush.InterpolationColors = colorBlend;
    //Create a transform for the brush. X and Y scale component must be equal to width and height of the rectangle correspondingly.
    //Translation components are offsets of the rectangle
    Matrix brushTransform = new Matrix(width, 0, 0, height, offsetX, offsetY);
    //Rotate the graphics state to get colors change in vertical direction from up to down
    brushTransform.Rotate(90);
    //Set the transform
    brush.Transform = brushTransform;

    //Set the paint
    document.SetPaint(brush);

    //Fill the rectangle
    document.Fill(path);

    //Close current page
    document.ClosePage();

    //Save the document
    document.Save();
}

结果如下

在此代码片段中，我们用两种颜色创建了一个对角线性渐变，并用该渐变填充了一个矩形。

//Create an output stream for PostScript document
using (Stream outPsStream = new FileStream(dataDir + "DiagonaGradient_outPS.ps", FileMode.Create))
{
    //Create save options with A4 size
    PsSaveOptions options = new PsSaveOptions();

    // Create new 1-paged PS Document
    PsDocument document = new PsDocument(outPsStream, options, false);

    float offsetX = 200;
    float offsetY = 100;
    float width = 200;
    float height = 100;

    //Create a graphics path from the first rectangle
    GraphicsPath path = new GraphicsPath();
    path.AddRectangle(new RectangleF(offsetX, offsetY, width, height));

    //Create linear gradient brush with the rectangle as bounds, start and end colors
    LinearGradientBrush brush = new LinearGradientBrush(new RectangleF(0, 0, width, height), Color.FromArgb(255, 255, 0, 0),
        Color.FromArgb(255, 0, 0, 255), 0f);

    //Create a transform for brush. X and Y scale component must be equal to width and height of the rectangle correspondingly.
    //Translation components are offsets of the rectangle        
    Matrix brushTransform = new Matrix(width, 0, 0, height, offsetX, offsetY);
    //Rotate the gradient, than scale and translate to get visible a color transition in required rectangle
    brushTransform.Rotate(-45);
    float hypotenuse = (float)System.Math.Sqrt(200 * 200 + 100 * 100);
    float ratio = hypotenuse / 200;
    brushTransform.Scale(-ratio, 1);
    brushTransform.Translate(100 / brushTransform.Elements[0], 0);

    //Set the transform
    brush.Transform = brushTransform;

    //Set the paint
    document.SetPaint(brush);

    //Fill the rectangle
    document.Fill(path);

    //Close current page
    document.ClosePage();

    //Save the document
    document.Save();
}

结果如下

在此代码片段中，我们创建了两种颜色的径向渐变，并用该渐变填充了一个圆圈。

//Create an output stream for PostScript document
using (Stream outPsStream = new FileStream(dataDir + "RadialGradient1_outPS.ps", FileMode.Create))
{
    //Create save options with A4 size
    PsSaveOptions options = new PsSaveOptions();

    // Create new 1-paged PS Document
    PsDocument document = new PsDocument(outPsStream, options, false);

    float offsetX = 200;
    float offsetY = 100;
    float width = 200;
    float height = 200;

    //Create a graphics path from the rectangle bounds
    RectangleF bounds = new RectangleF(offsetX, offsetY, width, height);
    GraphicsPath path = new GraphicsPath();
    path.AddEllipse(bounds);

    //Create and fill color blend object
    Color[] colors = { Color.White, Color.White, Color.Blue };
    float[] positions = { 0.0f, 0.2f, 1.0f };
    ColorBlend colorBlend = new ColorBlend();
    colorBlend.Colors = colors;
    colorBlend.Positions = positions;

    GraphicsPath brushRect = new GraphicsPath();
    brushRect.AddRectangle(new RectangleF(0, 0, width, height));

    //Create path gradient brush with the rectangle as bounds
    PathGradientBrush brush = new PathGradientBrush(brushRect);
    //Set interpolation colors
    brush.InterpolationColors = colorBlend;
    //Create a transform for the brush. X and Y scale component must be equal to width and height of the rectangle correspondingly.
    //Translation components are offsets of the rectangle
    Matrix brushTransform = new Matrix(width, 0, 0, height, offsetX, offsetY);
    //Set the transform
    brush.Transform = brushTransform;

    //Set the paint
    document.SetPaint(brush);

    //Fill the rectangle
    document.Fill(path);

    //Close current page
    document.ClosePage();

    //Save the document
    document.Save();
}

结果

在此代码片段中，我们创建了一个由 6 种颜色组成的径向渐变，并用该渐变填充了一个矩形。

//Create an output stream for PostScript document
using (Stream outPsStream = new FileStream(dataDir + "RadialGradient2_outPS.ps", FileMode.Create))
{
    //Create save options with A4 size
    PsSaveOptions options = new PsSaveOptions();

    // Create new 1-paged PS Document
    PsDocument document = new PsDocument(outPsStream, options, false);

    float offsetX = 200;
    float offsetY = 100;
    float width = 200;
    float height = 200;

    //Create a graphics path from the rectangle bounds
    RectangleF bounds = new RectangleF(offsetX, offsetY, width, height);
    GraphicsPath path = new GraphicsPath();
    path.AddRectangle(bounds);

    //Create and fill color blend object
    Color[] colors = { Color.Green, Color.Blue, Color.Black, Color.Yellow, Color.Beige, Color.Red };
    float[] positions = { 0.0f, 0.2f, 0.3f, 0.4f, 0.9f, 1.0f };
    ColorBlend colorBlend = new ColorBlend();
    colorBlend.Colors = colors;
    colorBlend.Positions = positions;

    GraphicsPath brushRect = new GraphicsPath();
    brushRect.AddRectangle(new RectangleF(0, 0, width, height));

    //Create path gradient brush with the rectangle as bounds
    PathGradientBrush brush = new PathGradientBrush(brushRect);
    //Set interpolation colors
    brush.InterpolationColors = colorBlend;
    //Create a transform for the brush. X and Y scale component must be equal to width and height of the rectangle correspondingly.
    //Translation components are offsets of the rectangle
    Matrix brushTransform = new Matrix(width, 0, 0, height, offsetX, offsetY);
    //Set the transform
    brush.Transform = brushTransform;

    //Set the paint
    document.SetPaint(brush);

    //Fill the rectangle
    document.Fill(path);

    //Close current page
    document.ClosePage();

    //Save the document
    document.Save();
}

结果

请参阅 Java 中 PS 文档中的渐变操作。

您可以从 GitHub 下载示例和数据文件。