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Java Polygons parameter "npoints"

I am currently trying my hands on a GameEngine and later on a Game and want to create an abstract class Hitbox, which gets extended by RectHitbox. Now when I create a Polygon Object, which I want to use to keep track of the shape, it also asks me for number of points npoints. I looked at this documentation but I don't know if "total number of points" refers to just the corner points or ALL points inside the area aswell.
Now my question is: is there is any advantage to automatically calculate the parameter npoints or if there is a disadvantage to leaving it Null.
What I mean by automatically calculate npoints (if it refers to the corner points):
public Hitbox(int x1, int y1, int x2, int y2){
xpoints[0] = x1;
xpoints[1] = x2;
ypoints[0] = y1;
ypoints[1] = y2;
polygon = new Polygon(xpoints, ypoints, xpoints.length+ypoints.length);
}
and what I mean by leaving it null:
public Hitbox(int x1, int y1, int x2, int y2){
xpoints[0] = x1;
xpoints[1] = x2;
ypoints[0] = y1;
ypoints[1] = y2;
polygon = new Polygon(xpoints, ypoints, null);
}

Astroid Draw Java Program Problems

I'm trying to generate an astroid (Not asteroid) graphic similar to this:
This graphic output is generated on a 400x400 DrawingPanel. And the math is based on making curves from straight lines. However, I'm having a problem with my x,y coordinates. instead of making the astroid, I'm generating this:
Here is the code:
import java.awt.*;
public class GraphicsProject
{
//main method
public static void main (String[]args){
//Initialize the variable
//The Window is 400 x 400 pixels in size
DrawingPanel panel = new DrawingPanel (400,400);
Graphics g = panel.getGraphics();
drawAstroid(g,0,0, 400);
}
public static void drawAstroid(Graphics g, int x, int y, int size){
int scale = size/40;
int x1, x2,x3, x4, y1, y2, y3, y4;
y1 = y;
y2 = y + size;
y3 = y + 1/2 * size;
y4 = y + 1/2 * size;
x1 = x + 1/2 * size;
x2 = x + 1/2 * size;
x3 = x + 1/2 * size;
x4 = x + 1/2 * size;
for (int i = 0; i < 21; i++ ){
//Draws Upper Left
g.drawLine(x4 - scale * i, y4, x1, y1 + scale * i);
//Draws Upper Right
g.drawLine(x4 + scale * i, y4, x2, y2 - scale * i);
//Draws Lower Left
g.drawLine(x3 - scale * i, y3, x4, y4 + scale * i);
//Draws Lower Right
g.drawLine(x3 + scale * i, y3, x2, y2 - scale * i);
}
}
}
Any insight into how to resolve this would be appreciated.

Debugging Java/Processing output of an object patrolling screen

I am a first year computer programming student working on a project of Robots and Robot testing environment.
Although I'm new to Stackoverflow, I'm pretty aware that we are not supposed to help with assignments or homework.
I'm struggling to understand why such behavior is happening, so it would be really helpful just to understand why it's happening.
We are using Processing libraries to program in Java.
Our task is to create a robot testing environment and create three robots performing different movements.
The movement I'm trying to program is Patrol, which means just go around the edges of the screen.
The expected behavior is to go forward until it reaches a wall, turn left (90 degrees counter-clock wise), and go forward again.
This project is in conjunction with our Math class. That being said, we can't use methods like rotate(), translate(), pushMatrix() and popMatrix() to help rotating the forms (each robot is a triangle).
So, the steps I followed to rotate the triangles were:
1) translate its center point to the origin (0,0) and the vertices using the same translation;
2) rotate all points, where (x, y) become (y, -x);
3) translate back to correct position (inverse of the step 1 translation).
I set some boundaries if statements to put the triangle back to screen if, after rotation, anything went off screen.
My problem
After turning, the triangle is appearing in strange position, like teleporting.
I added a few lines so we can get each vertex's coordinates, the direction it's going and detect when direction is changed.
Code
There are two files: TestRobots, Robot.
Robot:
import processing.core.PApplet;
public class Robot{
int colour;
String name;
float width;
float height;
float x1;
float y1;
float x2;
float y2;
float x3;
float y3;
int direction;
int speed;
float centralPointX = width/2;
float centralPointY = height/2;
PApplet parent;
public Robot(PApplet parent, String name, int colour, float x1, float y1, float x2, float y2, float x3, float y3, int speed){
this.parent = parent;
this.name = name;
this.colour = colour;
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
this.x3 = x3;
this.y3 = y3;
this.speed = speed;
direction=4;
width = x2-x3;
if (width < 0){
width *= -1;
}
if (y2 > y3){
height = y2-y1;
}else{
height = y3-y1;
}
if (height < 0){
height *= -1;
}
if (y1<y2 && y1<y3){
direction=4;
}
}
public void drawRobot(){
parent.fill(colour);
parent.triangle(x1, y1, x2, y2, x3, y3);
parent.ellipseMode(parent.CENTER);
parent.ellipse(x1, y1, 3, 3);
}
public void moveForward(){
if(x1<parent.width || y1 <parent.height || x1 > 0 || y1 > 0){
switch (direction){
case 1:
x1 += speed;
x2 += speed;
x3 += speed;
break;
case 2:
y1 += speed;
y2 += speed;
y3 += speed;
break;
case 3:
x1 -= speed;
x2 -= speed;
x3 -= speed;
break;
case 4:
y1 -= speed;
y2 -= speed;
y3 -= speed;
break;
}
}
}
public void turnLeft(){
//Store original coordinates.
float tempX1 = x1;
float tempY1 = y1;
float tempX2 = x2;
float tempY2 = y2;
float tempX3 = x3;
float tempY3 = y3;
//Calculate translation of the central point of triangle to the origin.
float xTranslation = 0 - centralPointX;
float yTranslation = 0 - centralPointY;
//Translate all points by the translation calculated.
float translatedX1 = tempX1 + xTranslation;
float translatedY1 = tempY1 + yTranslation;
float translatedX2 = tempX2 + xTranslation;
float translatedY2 = tempY2 + yTranslation;
float translatedX3 = tempX3 + xTranslation;
float translatedY3 = tempY3 + yTranslation;
//Rotate all points 90 degrees counterclockwise, (x, y) --> (y, -x).
float rotatedX1 = translatedY1;
float rotatedY1 = -translatedX1;
float rotatedX2 = translatedY2;
float rotatedY2 = -translatedX2;
float rotatedX3 = translatedY3;
float rotatedY3 = -translatedX3;
//Translate all points back.
x1 = rotatedX1 - xTranslation;
y1 = rotatedY1 - yTranslation;
x2 = rotatedX2 - xTranslation;
y2 = rotatedY2 - yTranslation;
x3 = rotatedX3 - xTranslation;
y3 = rotatedY3 - yTranslation;
//Check which y and which x are the smallest, in order to correct any negative numbers.
float minX;
float minY;
if (y1<y2 && y1<y3){
minY = y1;
} else if (y2<y1 && y2<y3){
minY = y2;
} else {
minY = y3;
}
if (x1<x2 && x1<x3){
minX = x1;
} else if (x2<x1 && x2<x3){
minX = x2;
} else {
minX = x3;
}
//Check which y and which x are the biggest, in order to correct any out-of-screen draws.
float maxX;
float maxY;
if (y1>y2 && y1>y3){
maxY = y1;
} else if (y2>y1 && y2>y3){
maxY = y2;
} else {
maxY = y3;
}
if (x1>x2 && x1>x3){
maxX = x1;
} else if (x2>x1 && x2>x3){
maxX = x2;
} else {
maxX = x3;
}
//Correct position if any coordinate is negative.
if((minY-speed)<=minY){
float differenceY = -minY + 10;
y1 += differenceY;
y2 += differenceY;
y3 += differenceY;
}
if(x1<=(x1-speed)){
float differenceX = -minX + 10;
x1 += differenceX;
x2 += differenceX;
x3 += differenceX;
}
//Correct position if any coordinate is bigger than the screen size.
if((parent.height<=(maxY+speed))){
float differenceY = (-maxY+parent.height) + 10;
y1 -= differenceY;
y2 -= differenceY;
y3 -= differenceY;
}
if((x1+speed)>=parent.width){
float differenceX = (-maxX+parent.width) + 10;
x1 -= differenceX;
x2 -= differenceX;
x3 -= differenceX;
}
//Change direction variable and adjust it between 0 and 4.
direction -=1;
if (direction == 0){
direction = 4;
}
}
public void patrol(){
System.out.println("Direction is: "+ direction);
if(((y1-speed)<= 0)||((y1+speed)>= parent.height) || ((x1+speed)>=parent.width)||((x1-speed)<=0)){
turnLeft();
System.out.println("The NEW direction is: "+ direction);
}
moveForward();
}
}
TestRobots:
import processing.core.PApplet;
public class TestRobots extends PApplet{
Robot alice = new Robot(this, "Alice", 255, 257f, 389f, 309f, 450f, 209f, 450f, 3);
public static void main(String[] args){
PApplet.main("TestRobots");
}
public void settings(){
size(1000, 500);
}
public void setup(){
frameRate(30);
}
public void draw(){
background(255);
alice.patrol();
System.out.println("x1 = "+ alice.x1);
System.out.println("y1 = "+ alice.y1);
System.out.println("x2 = "+ alice.x2);
System.out.println("y2 = "+ alice.y2);
System.out.println("x3 = "+ alice.x3);
System.out.println("y3 = "+ alice.y3);
alice.drawRobot();
}
}
Here is a print of the generated output. I snipped the part where it changes direction:
Direction is: 2
x1 = 62.0
y1 = 497.0
x2 = 10.0
y2 = 436.0
x3 = 110.0
y3 = 436.0
The NEW direction is: 1
x1 = 500.0
y1 = 58.0
x2 = 439.0
y2 = 110.0
x3 = 439.0
y3 = 10.0
Same strange behavior here:
Direction is: 4
x1 = 257.0
y1 = 2.0
x2 = 309.0
y2 = 63.0
x3 = 209.0
y3 = 63.0
The NEW direction is: 3
x1 = -1.0
y1 = 62.0
x2 = 60.0
y2 = 10.0
x3 = 60.0
y3 = 110.0
The NEW direction is: 2
x1 = 62.0
y1 = 74.0
x2 = 10.0
y2 = 13.0
x3 = 110.0
y3 = 13.0
Thank you very much for reading until here and sorry in advance if I wasn't clear enough. It's my first question!
Gustavo

I think your problem relates to the variables centralPointX and centralPointY. Look at this code you wrote:
//Calculate translation of the central point of triangle to the origin.
float xTranslation = 0 - centralPointX;
float yTranslation = 0 - centralPointY;
//Translate all points by the translation calculated.
float translatedX1 = tempX1 + xTranslation;
float translatedY1 = tempY1 + yTranslation;
float translatedX2 = tempX2 + xTranslation;
float translatedY2 = tempY2 + yTranslation;
float translatedX3 = tempX3 + xTranslation;
float translatedY3 = tempY3 + yTranslation;
It seems from this that you think centralPointX and centralPointY indicate the center of the triangle... However, look at where they are defined:
float centralPointX = width/2;
float centralPointY = height/2;
So they don't actually represent the center xy co-ordinates. What you need to do is fix this part:
//Calculate translation of the central point of triangle to the origin.
float xTranslation = 0 - centralPointX;
float yTranslation = 0 - centralPointY;
So that it actually does what the comment says it should do, i.e., calculates the x and y co-ordinates of the center of your triangle.
I won't implement this for you, because as you said, it is homework. However, I think this should definitely point you in the right direction. Also, keep up the good work. I wish every first question was as well thought out as this.

Java -- QuadCurve2D get Y by X

I use QuadCurve2D (Quadratic Curve Segment) in Java. Can I get y-coordinate by x-coordinate from this object?
Something like this:
QuadCurve2D q = new QuadCurve2D.Float ();
q.setCurve (x1, y1, ctrlx, ctrly, x2, y2);
int X = 100;
int Y = q.getY (X); // (?)

Cover polygon with rectangles Java

I need to cover some polygon with rectangles here's an example :
The black figure in a black square is the polygon that i need to cover with those green rectangles but i need to do it more efficiently that just make a net like i did. Because as you can see there can be place more green rectangles if i moved them.
Rectangles inside are fixed size(just not as big as polygon it self), one for all like in the picture, they can be places vertically and horizontally, i want to fill the polygon as much as it can fit it inside of it, this polygon is just for example, there can be different polygons with holes in them for example that black small square is a hole.
module = rectangle
private void coverWithModules(Graphics g, int[] xpoints, int[] ypoints) {
Polygon module;
int x1, x2, x3, x4, y1, y2, y3, y4;
int moduleRowNumber = 0;
int totalRows = (getMax(ypoints) / moduleHeight);
while (moduleRowNumber < totalRows) {
// first module
x1 = getMin(xpoints);
y1 = getMin(ypoints) + distance * moduleRowNumber + moduleHeight
* moduleRowNumber;
x2 = x1 + moduleWidth;
y2 = y1;
x3 = x1 + moduleWidth;
y3 = y1 + moduleHeight;
x4 = x1;
y4 = y1 + moduleHeight;
int[] x = { x1, x2, x3, x4 };
int[] y = { y1, y2, y3, y4 };
module = new Polygon();
// check if point are inside the polygon
checkModulePlacement(g, x, y, module);
// placing modules in a row
while (x1 < getMax(xpoints)) {
x1 = x2 + distance;
y1 = getMin(ypoints) + distance * moduleRowNumber
+ moduleHeight * moduleRowNumber;
x2 = x1 + moduleWidth;
y2 = y1;
x3 = x1 + moduleWidth;
y3 = y1 + moduleHeight;
x4 = x1;
y4 = y1 + moduleHeight;
int[] xx = { x1, x2, x3, x4 };
int[] yy = { y1, y2, y3, y4 };
module = new Polygon();
checkModulePlacement(g, xx, yy, module);
}
moduleRowNumber++;
}
}
private void checkModulePlacement(Graphics g, int[] x, int[] y, Polygon module) {
boolean pointInside = true;
boolean pointOnObstraction = true;
for (int i = 0; i < x.length; i++) {
if (pointInside) {
pointInside = roof.contains(x[i], y[i]);
}
module.addPoint(x[i], y[i]);
}
pointOnObstraction = checkForObstractions(module);
g.setColor(Color.GREEN);
if (pointInside == true && pointOnObstraction == false ) {
g.drawPolygon(module);
}
}
I was looking for something and i have found Something like this maybe there is more stuff like this ?
I don't know where to search for such info. What should i look up to get what i need ? Maybe there is some kind of library for this kind of things ?