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Java Graphics 2d avoid Polyline distorted corners

i'm working on a graphic interface for drawing subway maps. A line is represented with station as circles and a polyline to link them.You can move the stations with a mouseDrag and of course it updates the displaying map in real time. My problem is when stations comes to a certain angle, there is a polyline distortion and the corner created by the 2 lines is out of the station circle display, i'd like to know if there is a way to avoid this.
screenshots of the app with the polyline issue
here's my code for the polyline's draw
//x and y point array creation
xPoints = new int[this.stationViews.size()];
yPoints = new int[this.stationViews.size()];
for (int i=0;i<this.stationViews.size();i++) {
//fill arrays with the center point of circles representing stations
xPoints[i] = this.stationViews.get(i).getStation().getPosX()-this.stationViews.size()/2;
yPoints[i] = this.stationViews.get(i).getStation().getPosY()-this.stationViews.size();
}
//setting color
g2D.setColor(this.line.getColor());
//set stroke width relative to the zoom level
int strokeWidth=5;
if(!this.stationViews.isEmpty()) {
if (this.stationViews.get(0).getStationSize()>14) {
strokeWidth = this.stationViews.get(0).getStationSize()-13;
}else {
strokeWidth = 3;
}
}
g2D.setStroke(new BasicStroke(strokeWidth));
//draw the polyline
if (this.stationViews.size() >1) {
g2D.drawPolyline(xPoints, yPoints, this.stationViews.size());
}
//draw the station (g2D.drawCircle)
for (StationView stationView : stationViews) {
stationView.affiche(g2D,this.line.getColor());
}
thank you for your help

That is called the miter. You seem to be per default using JOIN_MITER, sharp joining of extended lines at the end, which can point far out of the join for small angles.
g2d.setStroke(new BasicStroke(strokeWidth,
BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND, 5));
miter a surface forming the beveled end or edge of a piece where a joint is made by cutting two pieces at an angle and fitting them together.
It is also a bishop's cap with a pointy top, hence the name.

Java - Get all pixels inside of a circle on a Buffered Image

I wasn't able to find the solution to this problem online, sorry if this question is already asked before, also I think my question's title wasn't specific enough, so, I will explain in more details.
So, what I did is created a BufferedImage with a specific size and type, let's say for example:
BufferedImage img1 = new BufferedImage(500, 500, BufferedImage.TYPE_INT_ARGB);
And what I am trying to do, is to use a "for" loop and loop thru every single image's pixel inside of an imaginary circle, lets say that circle starts on (X, Y)(0, 0), and ends on (X, Y)(500, 500).
Now, what I am trying to do, is to loop thru every single pixel inside of that imaginary circle, and then later, do something with that pixel (changing it's color for example).
Can anyone please help me do it? Thanks!

I came up with an idea that could solve this problem not only for circles, but also for any other shapes.
So, my idea is to create another Buffered Image, make it the same size as the one i want to edit (work on), make sure that all of it's pixels are blank (transparent), and draw a shape that you want on that new image (a circle for example) also, we keep the track of the shape's color, and the shape needs to be filled.
After that, we loop thru each pixel on the image that we want to edit using the for loops and the x, y integer variables, each time the loop repeats, we check on the shape's image to see if the shape is drawn there, and to do that we check if the pixel color is same as the shape's color on the shape's image. And if it is, the loop has detected the coordinates to the pixel inside of the shape, and then we can do something with it. (The for loops use the X and Y coordinate integers)
Here is an example code:
public static BufferedImage yourMethodName(BufferedImage inputImage, Point circlePosition, Dimension circleSize)
{
BufferedImage outputImage = inputImage;
BufferedImage circleImage = new BufferedImage(inputImage.getWidth(), inputImage.getHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics drawOnCircleImg = circleImage.getGraphics();
Color circleColor = new Color(0, 255, 0);
drawOnCircleImg.setColor(circleColor);
drawOnCircleImg.fillOval(circlePosition.x, circlePosition.y, circleSize.width, circleSize.height);
for(int y = 0; y < outputImage.getHeight(); y++)
{
for(int x = 0; x < outputImage.getWidth(); x++)
{
if(circleImage.getRGB(x, y) == circleColor.getRGB())
{
//PIXEL IS INSIDE OF THE SHAPE, IT IS DETECTED, DO SOMETHING NOW
//VARIABLES FOR THE PIXEL POSITION ARE: X, Y
}
}
}
return outputImage;
}

Drawing objects behind circle except the ones behind 'background'

Situation: I have a canvas on an Android game, I have some objects (I will keep it as simple as possible):World(where are storaged all Laser and Block objects), Block and Laser. I can draw all this objects in the canvas.
I would like to 'hide' them behind a black 'background', and then draw a blurry 'transparent' circle, so all objects are hidden behind the black background, except the objects behing the circle.
I have thought about it, but I can't think of an approach to do this.
Images:
This is my actual situation:
This is the expected:

Do something like this:
public void drawBitmapsInCanvas(Canvas c){
c.drawBitmap(block, new Rect(/*coordinates here*/), new Rect(/*More coordinates*/),null);
c.drawBitmap(block2, new Rect(/*coordinates here*/), new Rect(/*More coordinates*/),null);
c.drawBitmap(laser, new Rect(/*coordinates here*/), new Rect(/*More coordinates*/),null);
c.drawColor(Color.BLACK);//this hides everything under your black background.
c.drawBitmap(circle, new Rect(/*coordinates here*/), new Rect(/*More coordinates*/),null);
}
If you want transparency:
Paint paint =new Paint();
paint.setARGB(120,0,0,0); //for the "120" parameter, 0 is completely transparent, 255 is completely opaque.
paint.setAntiAlias(true);
c.drawBitmap(bmp,Rect r,Rect rr, paint);
or if you are trying to change the opacity of individual pixels, the approach is a bit more complicated (I have not tested the code, but you get the gist of it):
public static final Bitmap getNewBitmap(Bitmap bmp, int circleCenterX,
int circleCenterY,int circleRadius){
//CIRCLE COORDINATES ARE THE DISTANCE IN RESPECT OF (0,0) of the bitmap
//, not (0,0) of the canvas itself. The circleRadius is the circle's radius.
Bitmap temp=bmp.copy(Bitmap.Config.ARGB_8888, true);
int[]pixels = new int[temp.getWidth()*temp.getHeight()];
temp.getPixels(pixels,0 ,temp.getWidth(),0,0,temp.getWidth(), temp.getHeight());
int counter=0;
for(int i=0;i<pixels.length;i++){
int alpha=Color.alpha(pixels[i]);
if(alpha!=0&&!((Math.pow(counter/temp.getWidth()-circleCenterY,2.0)+
Math.pow(counter%temp.getWidth()-circleCenterX,2.0))<Math.pow(circleRadius,2.0))){
//if the pixel itself is not completely transparent and the pixel is NOT within range of the circle,
//set the Alpha value of the pixel to 0.
pixels[i]=Color.argb(0,Color.red(pixels[i]),Color.green(pixels[i]),Color.blue(pixels[i]));
}
counter++;
}
temp.setPixels(pixels,0, temp.getWidth(),0,0,temp.getWidth(),temp.getHeight());
return temp;
}
and then draw temp.
I'm not completely sure what you are trying to ask, so you may have to modify as necessary.

If you try the second answer of qwertyuiop5040, you will get a ver low - perfomance when you try to apply it to a large image. Let's say a 1000*800 pixels image. Then you will have a loop:
for (int i = 0 ; i < 1000*800; i++)

You could create an image that's a black rectangle with a transparent hole in it. The hole would be the circle that you can see through, and the image would be rendered over the spot you want to be visible. Then, you can draw four black rectangles around the image to cover the rest of the screen.

Android draw multiple Rect as background color

I used an canvas to draw multiple textures on it. these textures are rectangles and now I want to use these textures with parts of them invisble, so I could draw background colors behind the textures to have teh same texture with different colors without adding the same picture with different colors.
I tried to add Rects like this:
for(Coordinate c : ch.getVisibleCoords()) {
ShapeDrawable sD = new ShapeDrawable();
Rect r = new Rect(c.getxS(),
c.getyS(),
(sh.getScreenWidth()-c.getxS()-sh.getTSize()),
(sh.getScreenHeight()-c.getyS()-sh.getTSize()));
sD.setBounds(r);
textureColorRects.add(sD);
}
each coordinate represents an texture the xS and yS values are the positions at the screen, for example coordinate 1|1 could have xS=0 | yS=0 and 2|1 xS=48 (48=texturesize) | yS=0. I tried this with ShapeDrawable and Rectangles itself, in the first case it will draw everything the same color expect of one y-line and in the other case it will draw just some buggy shit.
Is there another way to do this or may I didn't understood how to setup those rectangles, I can't figure out how that left, top, right, bottom stuff works.
The rest of the code is here for you so you can see how I draw the ShapeDrawables:
int i = 0;
for(Coordinate c : ch.getVisibleCoords()) {
ShapeDrawable sD = textureColorRects.get(i);
Paint color = new Paint();
color.setColor(c.getLandscape().getType().getColor());
color.setStyle(Paint.Style.FILL);
sD.getPaint().set(color);
sD.draw(canvas);
}
The textureColorRects is a list containing all ShapeDrawables.
Thank you very much for reading.

I found an solution it's a problem other people had too (was just hard to find) it's a bit hard to understand how the Rect works the values for left, top, right and bottom are seen like the beginning and the ed point for example I want a rectangle of the size 16*16 and at the point x=5|y=18 on the screen, so I need to set the right value to x+size (5+16) and the bottom to y+size (18+16). The lft and top can be set to the left upper edge of the rect (start position).

Drawing a simple grid in canvas?

I've written Conway's Game Of Life in Java and I want to display it in a browser. I wanted to learn some Canvas, so what is the preferred way to draw a 2D grid and filling each cell in with a color? Thanks.

This will make a grid. It's useful I think for being able to position or determine the coordinates of an element or something, and several other possible handy use cases as well.
var grid = function() {
for (var i = 0; i < canvasWidth || i < canvasHeight; i += 100) { // 100 represents the width in pixels between each line of the grid
// draw horizontal lines
ctx.moveTo(i, 0);
ctx.lineTo(i, canvasHeight);
// draw vertical lines
ctx.moveTo(0, i);
ctx.lineTo(canvasWidth, i);
}
ctx.save();
ctx.strokeStyle = 'hsla(200, 0%, 20%, 0.8)';
ctx.stroke();
ctx.restore();
};
// Call the function
grid()
Hope this helps, and is what you're trying to do too. :)
edit: If you are looking to fill each grid square with a different color, then this function will not work, or could at least be used in combination with another function which creates and fills the squares in a similar way to the function above but cutting the width and height off based on the dimensions of the canvas width and height.