Beginner PROCESSING question about scan line and convex polygons? - processing

Question

I am new to processing and I need some help with this algorithm.
I cannot use the fill() and line() functions.
This should draw a convex polygon ( I choose the vertexes with mouse-clicks), and when I press the "T" button it will "fill()" the polygon.
int x1, y1, x2, y2;
int click;
boolean scanlineOn;
void setup() {
size(640, 480);
click = 0;
scanlineOn = false;
};
void draw() {
if (click == 2) {
beoszto(x1, y1, x2, y2);
click = 0;
x1 = -1;
y1 = -1;
x2 = -1;
y2 = -1;
};
if (scanlineOn == true) {
scanline();
scanlineOn = false;
};
};
void scanline() {
int x = 1, y = 1;
int xA = -1, yA = -1;
int xB = -1;
color a;
color b;
color c;
c = get(x, y);
while (x != 639 && y != 479) {
xA = -1;
yA = -1;
xB = -1;
while (x != 639) {
a = get(x, y);
b = get(x+1, y);
if (a != b && xA == -1) {
xA = x + 1;
yA = y;
c = get(xA, yA);
} else if (c == b && a != b) {
xB = x + 1;
};
if (xA != -1 && xB != -1){
myfill(xA, yA, xB);
xA = -1;
yA = -1;
xB = -1;
};
x = x + 1;
};
y = y + 1;
x = 1;
};
};
void myfill(int xA, int yA, int xB) {
while (xA < xB) {
point(xA, yA);
xA = xA + 1;
};
};
void beoszto(int x1, int y1, int x2, int y2) {
if (x1 < x2) {
sectiondraw(x2, y2, x1, y1);
} else if (x1 == x2 && y1 == y2) {
point(x1, y1);
} else {
sectiondraw(x1, y1, x2, y2);
};
};
void sectiondraw(int xA, int yA, int xB, int yB) {
int a, b, d, dE, dNE, a2, b2;
if (yA - yB <= 0) {
a2 = yB - yA;
} else {
a2 = yA - yB;
};
if (xA - xB <= 0) {
b2 = xB - xA;
} else {
b2 = xA - xB;
};
if (b2 >= a2) {
b = -b2;
a = a2;
} else {
b = -a2;
a = b2;
};
d = 2 * a + b;
dE = 2 * a;
dNE = 2 * (a + b);
point(xB, yB);
if (b2 >= a2 && yA >= yB) {
while (xB < xA) {
if (d >= 0) {
d = d - dE;
xB = xB + 1;
} else {
d = d - dNE;
yB = yB + 1;
xB = xB + 1;
};
point(xB, yB);
};
} else if (b2 >= a2 && yA < yB) {
while (xB < xA) {
if (d >= 0) {
d = d - dE;
xB = xB + 1;
} else {
d = d - dNE;
yB = yB - 1;
xB = xB + 1;
};
point(xB, yB);
};
} else if (b2 <= a2 && yA <= yB) {
while (yB > yA) {
if (d >= 0) {
d = d - dE;
yB = yB - 1;
} else {
d = d - dNE;
yB = yB - 1;
xB = xB + 1;
};
point(xB, yB);
};
} else {
while (yB < yA) {
if (d >= 0) {
d = d - dE;
yB = yB + 1;
} else {
d = d - dNE;
yB = yB + 1;
xB = xB + 1;
};
point(xB, yB);
};
};
};
void mousePressed() {
if (click == 0) {
x1 = mouseX;
y1 = mouseY;
click = 1;
} else {
x2 = mouseX;
y2 = mouseY;
click= 2;
};
};
void keyPressed() {
if (key == 't' || key == 'T') {
scanlineOn = true;
};
};
It is buggy like hell. My greatest problem is that I have to draw the polygon with multiple lines.

Answer 1

You should think about how you would do this with line() and/or fill(), then think about how to make your own functions for line() and fill().
Here's a hint: use an array to save the points you have clicked so far. One way to do that is like this:
int count = 0;
PVector[] vertices = new PVector[1000];
void mouseClicked() {
vertices[count] = new PVector(mouseX, mouseY);
count++;
}
Some formatting to keep in mind: in most (almost all) cases, you don't need a semicolon after a closed curly bracket. Whenever you have a semicolon inside the curly brackets, you don't need one afterward.

Answer 2

If you were to use the line() function you could make it like this:
//Create a list of all the clicked locations
ArrayList<PVector> clicked = new ArrayList<PVector>();
void setup(){
size(640, 480);
}
void draw(){
if(clicked.size() > 1){
for (int i = 1; i < clicked.size(); i++) {
//Draw a line between each clicked point
line(clicked.get(i).x,clicked.get(i).y,clicked.get(i-1).x,clicked.get(i-1).y);
}
}
}
void mousePressed(){
//Add new mouse presses to the list
clicked.add(new PVector(mouseX, mouseY));
}
Otherwise to not use the line() function you could create your own
void newLine(float x1, float y1, float x2, float y2){
float d = dist(x1,y1,x2,y2);
float m1 = (y2-y1)/d;
float m2 = (x2-x1)/d;
for (int i = 0; i < d; i++){
point(x1+i*m2, y1+i*m1);
}
}