Lesson: Getting Started with Graphics
The Java 2D API is powerful and complex. However, the vast majority of uses for the Java 2D API utilize a small subset of its capabilities encapsulated in the java.awt.Graphics class. This lesson covers the most common needs of applications developers. Less common needs are described later in the Advanced topics in the Java 2D API.
Most methods of the Graphics class can be divided into two basic groups:
- Draw and fill methods, enabling you to render basic shapes, text, and images
- Attributes setting methods, which affect how that drawing and filling appears
Methods such as setFont and setColor define how draw and fill methods render.
This figure illustrates how these methods relate to graphic objects:
- drawString – For drawing text
g.drawImage(img, 0, 0, width, height, 0, 0, imageWidth, imageHeight, null);
g2.draw(new Line2D.Double(0, 0, 30, 40));
Depending on your current need, you can choose one of several methods in the Graphics class based on the following criteria:
- Whether you want to render the image at the specified location in its original size or scale it to fit inside the given rectangle
- Whether you prefer to fill the transparent areas of the image with color or keep them transparent
Fill methods apply to geometric shapes and include fillArc , fillRect , fillOval , fillPolygon .
Whether you draw a line of text or an image, remember that in 2D graphics every point is determined by its x and y coordinates. All of the draw and fill methods need this information which determines where the text or image should be rendered.
For example, to draw a line, an application calls the following:
java.awt.Graphics.drawLine(int x1, int y1, int x2, int y2)
In this code (x1, y1) is the start point of the line, and (x2, y2) is the end point of the line.
So the code to draw a horizontal line is as follows:
Graphics.drawLine(20, 100, 120, 100);
The demo below accumulates all mentioned techniques. Move the slider to display various weather types.
Note: If you don’t see the applet running, you need to install at least the Java SE Development Kit (JDK) 7 release.
The WeatherWizard demo uses the JSlider component as well as various graphics capabilities to generate and display a specified weather type. For more information about the JSlider class see the How to Use Sliders section of the Swing Tutorial.
The paint method of the WeatherPainter class implements graphics features. The following code draws an image determined by using the setupWeatherReport() method.
. origComposite = g2.getComposite(); if (alpha0 != null) g2.setComposite(alpha0); g2.drawImage(img0, 0, 0, size.width, size.height, 0, 0, img0.getWidth(null), img0.getHeight(null), null); if (img1 != null) < if (alpha1 != null) g2.setComposite(alpha1); g2.drawImage(img1, 0, 0, size.width, size.height, 0, 0, img1.getWidth(null), img1.getHeight(null), null); >.
The setFont and drawString methods render the temperature and the weather condition.
. // Freezing, Cold, Cool, Warm, Hot, // Blue, Green, Yellow, Orange, Red Font font = new Font("Serif", Font.PLAIN, 36); g.setFont(font); String tempString = feels + " " + temperature+"F"; FontRenderContext frc = ((Graphics2D)g).getFontRenderContext(); . g.setColor(textColor); int xTextTemp = rX-(int)boundsTemp.getX(); int yTextTemp = rY-(int)boundsTemp.getY(); g.drawString(tempString, xTextTemp, yTextTemp); int xTextCond = rX-(int)boundsCond.getX(); int yTextCond = rY-(int)boundsCond.getY() + (int)boundsTemp.getHeight(); g.drawString(condStr, xTextCond, yTextCond); The fillRect method allows you to draw a rectangle filled with the specified color.
. Rectangle2D boundsTemp = font.getStringBounds(tempString, frc); Rectangle2D boundsCond = font.getStringBounds(condStr, frc); int wText = Math.max((int)boundsTemp.getWidth(), (int)boundsCond.getWidth()); int hText = (int)boundsTemp.getHeight() + (int)boundsCond.getHeight(); int rX = (size.width-wText)/2; int rY = (size.height-hText)/2; g.setColor(Color.LIGHT_GRAY); g2.fillRect(rX, rY, wText, hText); .
Try to modify the WeatherWizard demo to alter the graphical content. For example, use the fillRoundRect method instead of fillRect or apply another font size in the setFont method. Find the complete code for this applet in the WeatherWizard.java file. The demo also requires the following images: weather-cloud.png , weather-rain.png , weather-snow.png , and weather-sun.png located in the images directory.
Trail: 2D Graphics
This trail introduces you to the Java 2D™ API and shows you how to display and print 2D graphics in your Java programs. The trail is intended for developers who want to enrich their knowledge of the Java 2D API, as well as for beginners in computer graphics. Almost every section contains relevant examples to illustrate specific capabilities. The Java 2D API enables you to easily perform the following tasks:
- Draw lines, rectangles and any other geometric shape.
- Fill those shapes with solid colors or gradients and textures.
- Draw text with options for fine control over the font and rendering process.
- Draw images, optionally applying filtering operations.
- Apply operations such as compositing and transforming during any of the above rendering operations.
This chapter also explains less familiar concepts such as compositing.
Using 2D Graphics API to display complex charts
Using image-filtering operations
This chapter describes the concept of drawing on-screen and off-screen images, as well as surfaces and printer devices. This trail covers the most common uses of the Java 2D APIs and briefly describes some of the more advanced features.
Overview of the Java 2D Graphics API introduces the key Java 2D concepts and describes the Java 2D rendering model. This lesson is more conceptual than other lessons of this trail, it enables you to get deep into basic notions and classes descriptions.
Getting started with Graphics uses a developed example to show you how to obtain a Graphics object and use it for common graphics rendering tasks.
Working with Geometry teaches you how to use APIs to draw graphic primitives and arbitrary shapes, and how to apply fancy strokes and fill styles.
Working with Text APIs shows you how to effectively use text APIs, including how to create a Font object with desired attributes, measure text, and determine the names of the fonts available on your system.
Working with Images explains how to create a BufferedImage object, perform image-filtering operations, and draw on an image.
Printing teaches you how to render 2D graphics to a printer, print complex documents, and use Print Services.
Advanced topics in Java 2D explains how to perform transformations, clip the drawing region, composite overlapping graphics, specify rendering preferences, and control rendering quality.