7. AWT Graphics

7. AWT Graphics
	Chapter 10. Graphic User Interface

7.1. Graphics Object

7.1.1. Definition

Graphics objects are the key to all drawing. They support the two basic kinds of drawing: primitive graphics (such as lines, rectangles, and text) and images. They also provide a drawing context by maintaining state such as the current drawing area and the current drawing color.

7.1.2. The Coordinate System

Figure 10.34. Coordinate System

	Note
	Each `Component` has its own integer coordinate system, ranging from (0, 0) to (width - 1, height - 1).

7.1.3. Drawing Shapes

The Graphics class defines methods for drawing the following kinds of shapes:

Lines: drawLine(), which draws a line in the Graphics object's current color, which is initialized to the Component's foreground color.
Rectangles: drawRect(), fillRect(), and clearRect() -- where fillRect() fills a rectangle with the Graphics object's current color, and clearRect() fills a rectangle with the Component's background color.
Raised or lowered rectangles:draw3DRect() and fill3DRect().
Round-edged rectangles:drawRoundRect() and fillRoundRect().
Ovals:drawOval() and fillOval().
Arcs:drawArc() and fillArc().
Polygons:drawPolygon() and fillPolygon().

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7.1.4. A Shape Sampler

Figure 10.35. Shape Sampler

Code:

Color bg = getBackground();
Color fg = getForeground();
. . .
// drawLine()
g.drawLine(x, y + rectHeight, x + rectWidth, y); // x1, y1, x2, y2
. . .
// drawRect()
g.drawRect(x, y, rectWidth, rectHeight); // x, y, width, height
. . .
// draw3DRect() 
g.setColor(bg);
g.draw3DRect(x, y, rectWidth, rectHeight, true);
g.setColor(fg);
. . .
// drawArc() 
g.drawArc(x, y, rectWidth, rectHeight, 90, 135); // x, y, w, h
. . .
// drawPolygon() 
Polygon polygon = new Polygon();
polygon.addPoint(x, y);
polygon.addPoint(x+rectWidth, y+rectHeight);
polygon.addPoint(x, y+rectHeight);
polygon.addPoint(x+rectWidth, y);
//polygon.addPoint(x, y); //don't complete; fill will, draw won't
g.drawPolygon(polygon); 
. . .
// fillRect() 
g.fillRect(x, y, rectWidth, rectHeight); // x, y, width, height
. . .
// fill3DRect() 
g.setColor(bg);
g.fill3DRect(x, y, rectWidth, rectHeight, true);
g.setColor(fg);
. . .
// fillArc() 
g.fillArc(x, y, rectWidth, rectHeight, 90, 135); // x, y, w, h
. . .
// fillPolygon() 
Polygon filledPolygon = new Polygon();
filledPolygon.addPoint(x, y);
filledPolygon.addPoint(x+rectWidth, y+rectHeight);
filledPolygon.addPoint(x, y+rectHeight);
filledPolygon.addPoint(x+rectWidth, y);
//filledPolygon.addPoint(x, y);
g.fillPolygon(filledPolygon);

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7.1.5. DrawingText

Figure 10.36. Drawing Text

7.1.5.1. Graphics Methods for drawing text

public void drawString(String data, int x, int y);
public void drawChars(char data[], int offset, int length, int x, int y);
public void drawBytes(byte data[], int offset, int length, int x, int y);

	Note
	For the text drawing methods, x and y are integers that specify the position of the lower left corner of the text. To be precise, the y coordinate specifies the baseline of the text.

7.1.5.2. FontMetrics objects are used to get information about a font

boolean textFits = false;
Font font = g.getFont();
FontMetrics fontMetrics = g.getFontMetrics();
while (!textFits) {
    if ((fontMetrics.getHeight() <= maxCharHeight) &&
        (fontMetrics.stringWidth("drawRoundRect()") <= gridWidth)) {
        textFits = true;
    } else {
        g.setFont(font = new Font(font.getName(), font.getStyle(),
                                  font.getSize() - 1));
        fontMetrics = g.getFontMetrics();
    }
}

Methods that return information about a font's vertical size:

getAscent(), getMaxAscent(), getDescent(), getMaxDescent(), getHeight(), getLeading()

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6. Layout Managers		8. Images