Gray Code Counter
This orientation to the Logisim libraries concludes with a fairly sophisticated Gray code counter that allows the user to alter its current value using the Poke Tool and to place a label on the component using the Text Tool. It also customizes the icon that appears in the explorer, associated with the tool.
GrayCounter
package com.cburch.gray;
import java.net.URL;
import javax.swing.ImageIcon;
import com.cburch.logisim.data.Attribute;
import com.cburch.logisim.data.BitWidth;
import com.cburch.logisim.data.Bounds;
import com.cburch.logisim.data.Direction;
import com.cburch.logisim.instance.Instance;
import com.cburch.logisim.instance.InstanceFactory;
import com.cburch.logisim.instance.InstancePainter;
import com.cburch.logisim.instance.InstanceState;
import com.cburch.logisim.instance.Port;
import com.cburch.logisim.instance.StdAttr;
import com.cburch.logisim.util.GraphicsUtil;
import com.cburch.logisim.util.StringUtil;
/** Manufactures a counter that iterates over Gray codes. This demonstrates
* several additional features beyond the SimpleGrayCounter class. */
class GrayCounter extends InstanceFactory {
public GrayCounter() {
super("Gray Counter");
setOffsetBounds(Bounds.create(-30, -15, 30, 30));
setPorts(new Port[] {
new Port(-30, 0, Port.INPUT, 1),
new Port( 0, 0, Port.OUTPUT, StdAttr.WIDTH),
});
// We'll have width, label, and label font attributes. The latter two
// attributes allow us to associate a label with the component (though
// we'll also need configureNewInstance to configure the label's
// location).
setAttributes(
new Attribute[] { StdAttr.WIDTH, StdAttr.LABEL, StdAttr.LABEL_FONT },
new Object[] { BitWidth.create(4), "", StdAttr.DEFAULT_LABEL_FONT });
// The following method invocation sets things up so that the instance's
// state can be manipulated using the Poke Tool.
setInstancePoker(CounterPoker.class);
// These next two lines set it up so that the explorer window shows a
// customized icon representing the component type. This should be a
// 16x16 image.
URL url = getClass().getClassLoader().getResource("com/cburch/gray/counter.gif");
if(url != null) setIcon(new ImageIcon(url));
}
/** The configureNewInstance method is invoked every time a new instance
* is created. In the superclass, the method doesn't do anything, since
* the new instance is pretty thoroughly configured already by default. But
* sometimes you need to do something particular to each instance, so you
* would override the method. In this case, we need to set up the location
* for its label. */
protected void configureNewInstance(Instance instance) {
Bounds bds = instance.getBounds();
instance.setTextField(StdAttr.LABEL, StdAttr.LABEL_FONT,
bds.getX() + bds.getWidth() / 2, bds.getY() - 3,
GraphicsUtil.H_CENTER, GraphicsUtil.V_BASELINE);
}
public void propagate(InstanceState state) {
// This is the same as with SimpleGrayCounter, except that we use the
// StdAttr.WIDTH attribute to determine the bit width to work with.
BitWidth width = state.getAttributeValue(StdAttr.WIDTH);
CounterData cur = CounterData.get(state, width);
boolean trigger = cur.updateClock(state.getPort(0));
if(trigger) cur.setValue(GrayIncrementer.nextGray(cur.getValue()));
state.setPort(1, cur.getValue(), 9);
}
public void paintInstance(InstancePainter painter) {
// This is essentially the same as with SimpleGrayCounter, except for
// the invocation of painter.drawLabel to make the label be drawn.
painter.drawBounds();
painter.drawClock(0, Direction.EAST);
painter.drawPort(1);
painter.drawLabel();
if(painter.getShowState()) {
BitWidth width = painter.getAttributeValue(StdAttr.WIDTH);
CounterData state = CounterData.get(painter, width);
Bounds bds = painter.getBounds();
GraphicsUtil.drawCenteredText(painter.getGraphics(),
StringUtil.toHexString(width.getWidth(), state.getValue().toIntValue()),
bds.getX() + bds.getWidth() / 2,
bds.getY() + bds.getHeight() / 2);
}
}
}
CounterPoker
package com.cburch.gray;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;
import com.cburch.logisim.data.BitWidth;
import com.cburch.logisim.data.Bounds;
import com.cburch.logisim.data.Value;
import com.cburch.logisim.instance.InstancePainter;
import com.cburch.logisim.instance.InstancePoker;
import com.cburch.logisim.instance.InstanceState;
import com.cburch.logisim.instance.StdAttr;
/** When the user clicks a counter using the Poke Tool, a CounterPoker object
* is created, and that object will handle all user events. Note that
* CounterPoker is a class specific to GrayCounter, and that it must be a
* subclass of InstancePoker in the com.cburch.logisim.instance package. */
public class CounterPoker extends InstancePoker {
public CounterPoker() { }
/** Determines whether the location the mouse was pressed should result
* in initiating a poke.
*/
public boolean init(InstanceState state, MouseEvent e) {
return state.getInstance().getBounds().contains(e.getX(), e.getY());
// Anywhere in the main rectangle initiates the poke. The user might
// have clicked within a label, but that will be outside the bounds.
}
/** Draws an indicator that the caret is being selected. Here, we'll draw
* a red rectangle around the value. */
public void paint(InstancePainter painter) {
Bounds bds = painter.getBounds();
BitWidth width = painter.getAttributeValue(StdAttr.WIDTH);
int len = (width.getWidth() + 3) / 4;
Graphics g = painter.getGraphics();
g.setColor(Color.RED);
int wid = 7 * len + 2; // width of caret rectangle
int ht = 16; // height of caret rectangle
g.drawRect(bds.getX() + (bds.getWidth() - wid) / 2,
bds.getY() + (bds.getHeight() - ht) / 2, wid, ht);
g.setColor(Color.BLACK);
}
/** Processes a key by just adding it onto the end of the current value. */
public void keyTyped(InstanceState state, KeyEvent e) {
// convert it to a hex digit; if it isn't a hex digit, abort.
int val = Character.digit(e.getKeyChar(), 16);
BitWidth width = state.getAttributeValue(StdAttr.WIDTH);
if(val < 0 || (val & width.getMask()) != val) return;
// compute the next value
CounterData cur = CounterData.get(state, width);
int newVal = (cur.getValue().toIntValue() * 16 + val) & width.getMask();
Value newValue = Value.createKnown(width, newVal);
cur.setValue(newValue);
state.fireInvalidated();
// You might be tempted to propagate the value immediately here, using
// state.setPort. However, the circuit may currently be propagating in
// another thread, and invoking setPort directly could interfere with
// that. Using fireInvalidated notifies the propagation thread to
// invoke propagate on the counter at its next opportunity.
}
}
Next: Guidelines.
