Working with Vector Graphics

In this chapter, we’ll explore how to use the powerful GraphicsAbsorber class to interact with vector graphics within PDF documents. Whether you need to move, remove, or add graphics, this guide will show you how to perform these tasks effectively.

Introduction

Vector graphics are a crucial component of many PDF documents, used to represent images, shapes, and other graphical elements. Aspose.PDF provides the GraphicsAbsorber class, which allows developers to programmatically access and manipulate these graphics. By using the Visit method of GraphicsAbsorber, you can extract vector graphics from a specified page and perform various operations, such as moving, removing, or copying them to other pages.

Extracting Graphics with GraphicsAbsorber

The first step in working with vector graphics is to extract them from a PDF document. Here’s how you can do it using the GraphicsAbsorber class:

public static void UsingGraphicsAbsorber()
{
    // Step 1: Create a Document object.
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");

    // Step 2: Create an instance of GraphicsAbsorber.
    var graphicsAbsorber = new GraphicsAbsorber();

    // Select the first page of the document.
    var page = document.Pages[1];

    // Step 3: Use the `Visit` method to extract graphics from the page.
    graphicsAbsorber.Visit(page);

    // Display information about the extracted elements.
    foreach (var element in graphicsAbsorber.Elements)
    {
        Console.WriteLine($"Page Number: {element.SourcePage.Number}");
        Console.WriteLine($"Position: ({element.Position.X}, {element.Position.Y})");
        Console.WriteLine($"Number of Operators: {element.Operators.Count}");
    }
}

1. Create a Document Object: A new Document object is instantiated with the path to the target PDF file.
2. Create an Instance of GraphicsAbsorber: This class captures all graphics elements from a specified page.
3. Visit Method: The Visit method is called on the first page, allowing GraphicsAbsorber to absorb the vector graphics.
4. Iterate Through Extracted Elements: The code loops through each extracted element, printing information such as page number, position, and the number of drawing operators involved.

Moving Graphics

Once you have extracted the graphics, you can move them to a different position on the same page. Here’s how you can achieve this:

public static void MoveGraphics()
{
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");
    var graphicsAbsorber = new GraphicsAbsorber();
    var page = document.Pages[1];
    graphicsAbsorber.Visit(page);

    // Temporarily suspend updates to improve performance.
    graphicsAbsorber.SuppressUpdate();

    foreach (var element in graphicsAbsorber.Elements)
    {
        var position = element.Position;
        // Move graphics by shifting its X and Y coordinates.
        element.Position = new Point(position.X + 150, position.Y - 10);
    }

    // Resume updates and apply changes.
    graphicsAbsorber.ResumeUpdate();
    document.Save("test.pdf");
}

• SuppressUpdate: This method temporarily suspends updates to improve performance when making multiple changes.
• ResumeUpdate: This method resumes updates and applies changes made to the graphics’ positions.
• Element Positioning: The position of each graphic is adjusted by changing its X and Y coordinates.

Removing Graphics

There are scenarios where you might want to remove specific graphics from a page. Aspose.PDF offers two methods to accomplish this:

Method 1: Using Rectangle Boundary

public static void RemoveGraphicsMethod1()
{
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");
    var graphicsAbsorber = new GraphicsAbsorber();
    var page = document.Pages[1];
    graphicsAbsorber.Visit(page);
    var rectangle = new Rectangle(70, 248, 170, 252);

    graphicsAbsorber.SuppressUpdate();
    foreach (var element in graphicsAbsorber.Elements)
    {
        // Check if the graphic's position falls within the rectangle.
        if (rectangle.Contains(element.Position))
        {
            element.Remove(); // Remove the graphic element.
        }
    }
    graphicsAbsorber.ResumeUpdate();
    document.Save("test.pdf");
}

Method 2: Using a Collection of Removed Elements

public static void RemoveGraphicsMethod2()
{
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");
    var graphicsAbsorber = new GraphicsAbsorber();
    var page = document.Pages[1];
    var rectangle = new Rectangle(70, 248, 170, 252);

    graphicsAbsorber.Visit(page);
    var removedElementsCollection = new GraphicElementCollection();
    foreach (var item in graphicsAbsorber.Elements.Where(el => rectangle.Contains(el.Position)))
    {
        removedElementsCollection.Add(item);
    }

    page.Contents.SuppressUpdate();
    page.DeleteGraphics(removedElementsCollection);
    page.Contents.ResumeUpdate();
    document.Save("test.pdf");
}

• Rectangle Boundary: Define a rectangle area to specify which graphics to remove.
• Suppress and Resume Updates: Ensure efficient removal without intermediate rendering.

Adding Graphics to Another Page

Graphics absorbed from one page can be added to another page within the same document. Here are two methods to achieve this:

Method 1: Adding Graphics Individually

public static void AddToAnotherPageMethod1()
{
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");
    var graphicsAbsorber = new GraphicsAbsorber();
    var page1 = document.Pages[1];
    var page2 = document.Pages[2];

    graphicsAbsorber.Visit(page1);
    page2.Contents.SuppressUpdate();
    foreach (var element in graphicsAbsorber.Elements)
    {
        element.AddOnPage(page2); // Add each graphic element to the second page.
    }
    page2.Contents.ResumeUpdate();
    document.Save("test.pdf");
}

Method 2: Adding Graphics as a Collection

public static void AddToAnotherPageMethod2()
{
    var document = new Document(@"C:\Samples\Sample-Document-01.pdf");
    var graphicsAbsorber = new GraphicsAbsorber();
    var page1 = document.Pages[1];
    var page2 = document.Pages[2];

    graphicsAbsorber.Visit(page1);
    page2.Contents.SuppressUpdate();
    page2.AddGraphics(graphicsAbsorber.Elements); // Add all graphics at once.
    page2.Contents.ResumeUpdate();
    document.Save("test.pdf");
}

• SuppressUpdate and ResumeUpdate: These methods help in maintaining performance while making bulk changes.
• AddOnPage vs. AddGraphics: Use AddOnPage for individual additions and AddGraphics for bulk additions.