1. Barb Ericson Georgia Institute of Technology May 2006
Speed part 2
Barb Ericson
Georgia Institute of Technology
May 2006
Georgia Institute of Technology

2. Georgia Institute of Technology
Learning Goals
Gain some understanding of interpreters
Write a simple interpreter that understands a simple graphical language
Interpret the graphical language and produce the expected result
Add more functionality to that interpreter
Connect this to what is happening in Flash, AutoCAD, etc,
Think about what is faster an interpreter or just the commands created by the interpreter
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3. Creating an Interpreter
Create a class GraphicsInterpreter
that has a method interpretCommands that takes the name of a file
Read graphics commands from the file and execute the commands on a blank 640 by 480 picture
line
Draw a line from (10,20) to (300,400)
Circle
Draw a circle with the upper left corner of the enclosing rectangle at (100,200) and a diameter of 10
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4. interpretCommands Method
public Picture interpretCommands(String fileName) {
String line = null;
Picture frame = new Picture(640,480);
String [] params = null;
int x1, y1, x2, y2, diameter;
Graphics g = frame.getGraphics();
g.setColor(Color.black);
// try the following
try {
// read from the file
BufferedReader reader =
new BufferedReader(new FileReader(fileName));
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5. interpretCommands Method – Cont1
// loop till end of file
while ((line = reader.readLine()) != null) {
// what command is this?
if (line.startsWith("line"))
// Get the parameters for drawing the line
params = line.split(" ");
// params[0] should be "line"
x1 = Integer.parseInt(params[1]);
y1 = Integer.parseInt(params[2]);
x2 = Integer.parseInt(params[3]);
y2 = Integer.parseInt(params[4]);
// Now, draw the line in
g.drawLine(x1,y1,x2,y2); }
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6. interpretCommands Method – Cont2
else if (line.startsWith("circle")) {
// Get the parameters for drawing the circle
params = line.split(" ");
// params[0] should be "circle"
x1 = Integer.parseInt(params[1]);
y1 = Integer.parseInt(params[2]);
diameter = Integer.parseInt(params[3]);
// Now, draw the circle in
g.drawOval(x1,y1,diameter,diameter); }
else
System.out.println("Uh-oh! Invalid command! "+line);
return frame;
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7. interpretCommands Method – Cont3
} // end while
} catch (FileNotFoundException ex) {
System.out.println("Couldn't find file " + fileName);
fileName = FileChooser.pickAFile();
interpretCommands(fileName);
} catch (Exception ex) {
System.out.println("Error during read or write");
ex.printStackTrace(); }
return frame;
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8. Georgia Institute of Technology
Main for Testing
public static void main(String[] args) {
GraphicsInterpreter interpreter =
new GraphicsInterpreter();
String fileName =
FileChooser.getMediaPath("graphics-commands.txt");
Picture p = interpreter.interpretCommands(fileName);
p.show(); }
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9. Georgia Institute of Technology
Resulting Picture
Commands:
circle
circle
line
line
line
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10. Georgia Institute of Technology
How This Works
Create a blank 640 by 480 picture and get the graphics context for drawing
Open the file to read from and loop reading a line at a time
Check if the current line starts with "line" or "circle"
If it starts with line get the next 4 numbers as the first point and second point x and y values and draw the line
If it starts with circle get the next 3 numbers as the upper left corner and diameter and draw the circle
Return the resulting picture object
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11. The Graphics Interpreter
We have just created a simple graphical language
That is used to represent lines and circles
And an interpreter that understands that language
This is what Flash, AutoCAD, Postscript, and PDF do, too
The file formats specify the language
And they interpret the language and draw the image
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12. Which will execute faster?
Our GraphicsInterpreter
Drawing the last picture using the interpretCommands method on the sample input
Or, the GeneratedDrawing class main at right?
import java.awt.*;
public class GeneratedDrawing{
public static void main(String args[]){
Picture frame = new Picture(640,480);
Graphics g = frame.getGraphics();
g.setColor(Color.black);
g.drawOval(20,20,100,100);
g.drawOval(300,20,100,100);
g.drawLine(210,120,210,320);
g.drawLine(210,320,310,320);
g.drawLine(20,350,400,350);
frame.show();
} // end main()
} // end class
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13. Interpreters are Slower
The GeneratedDrawing class main will execute faster
It doesn't need to interpret the commands
Just execute them
Think of talking to a native versus a non-native speaker through an interpreter
A conversation will take longer with an interpreter in the middle
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14. Georgia Institute of Technology
Exercise
Add the ability to draw triangles to the GraphicsInterpreter class
triangle x1 y1 x2 y2 x3 y3
It will draw a triangle with points at (x1,y1), (x2,y2), and (x3, y3)
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15. Georgia Institute of Technology
Summary
Interpreters read a language and execute the commands in that language
You can write an interpreter for a simple graphics language
Interpreters are slower than just executing the code that is being created
You have to read the language and figure out what to do
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