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Java OpenGL rotate text from center point

I am trying to rotate a text using JOGL but it does not rotate from the center point. What can I do with the following code to rotate from the center of the text?
TextRenderer textRenderer = new TextRenderer(new Font("SansSerif", Font.PLAIN, 20));
textRenderer.setColor(Color.WHITE);
textRenderer.beginRendering(viewport.width, viewport.height, false);
gl.glMatrixMode(GL2.GL_MODELVIEW);
gl.glPushMatrix();
gl.glTranslated(screenPoint.x, screenPoint.y, 0);
gl.glRotated(rotation, 0, 0, 1);
gl.glTranslated(-screenPoint.x, -screenPoint.y, 0);
textRenderer.draw("Text", (int) screenPoint.x, (int) screenPoint.y);
textRenderer.endRendering();
gl.glMatrixMode(GL2.GL_MODELVIEW);
gl.glPopMatrix();
textRenderer.flush();

Android studio canvas get center

look I am new to android but have some java knowledge
I learnt
to draw text in canvas
to get width
to get height
but how to put the text in the centre of canvas no matter how big the device, the canvas is
I want to do this in java without XML change.

Try this :
Paint text = new Paint();
text.setTextAlign(Paint.Align.CENTER);
int xPosition = (canvas.getWidth() / 2);
int yPosition = (int) ((canvas.getHeight() / 2) - ((text.descent() + text.ascent()) / 2)) ;
canvas.drawText("Hello World", xPosition, yPosition, text);

How do I place a programatically generated bitmap in a View?

I've generated a circle bitmap programatically like so:
private Bitmap drawDotCircle() {
int circleSize = 100;
circleBitmap = Bitmap.createBitmap(
circleSize,
circleSize,
Bitmap.Config.ARGB_8888
);
canvas = new Canvas(circleBitmap);
CanvasRadius = Math.min(canvas.getWidth(), canvas.getHeight() / 2);
// Create a Paint object used to paint the circle
paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.RED);
paint.setAntiAlias(true);
canvas.drawCircle(
canvas.getWidth() / 2,
canvas.getHeight() / 2,
CanvasRadius - CanvasPadding,
paint
);
return circleBitmap;
}
I would like to place it at an absolute X and Y that I've calculated; let's assume its the absolute center of the screen as follows:
int dotX =getResources().getDisplayMetrics().widthPixels / 2;
int dotY = getResources().getDisplayMetrics().heightPixels / 2;
How do I ensure that the circle is centered in the view? I have tried the following code, but the circle is always off-center for some reason:
RelativeLayout.LayoutParams layoutParams =
new RelativeLayout.LayoutParams(circleDot.getHeight(), circleDot.getHeight());
// Setting position of our ImageView
layoutParams.leftMargin = dotX;
layoutParams.topMargin = dotY;
// Finally Adding the imageView to RelativeLayout and its position
relativeLayout.addView(dotView, layoutParams);

The leftMargin should be dotX - imageWidth/2 and topMargin should be dotY - imageHeight/2
Try that

Kaleidoscope Effect in Android

I'm trying to create a Kaleidoscope with an ImageView in Android. I'm struggling to get the rotation and mirroring for each 'segment' correct. I'm new to image manipulation and I'm trying to adapt the code example from here for android.
I have the following code:
private void drawKaleidoscope() {
Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.cropped_landscape);
Bitmap imageview_bitmap = Bitmap.createBitmap(bm.getWidth(), bm.getHeight(), Bitmap.Config.ARGB_8888);
Bitmap matrix_bitmap;
BitmapShader fillShader;
Path triangle_mask = new Path();
RectF r = new RectF(0, 0, bm.getWidth(), bm.getHeight()); // create new rectangle to match the dimensions of our image
this.radius = (int)r.height() / 2;
Canvas c = new Canvas(imageview_bitmap);
c.drawColor(Color.BLACK);
float start_angle = 0;
for (int i = 0; i < this.segments; i++) {
// Create pie-slice shape mask
triangle_mask.reset();
triangle_mask.moveTo(r.centerX(), r.centerY());
triangle_mask.arcTo(r, start_angle, angle);
triangle_mask.close();
// Use odd even check to decide when to mirror the image or not
if (i % 2 == 0) {
Matrix mat = new Matrix();
mat.preTranslate(-radius, -radius);
mat.postRotate(i * angle);
mat.postTranslate(radius, radius);
matrix_bitmap = Bitmap.createBitmap(bm, 0, 0, (int)r.width(), (int)r.height(), mat, true);
}
else {
Matrix mat = new Matrix();
// mirror on x axis
mat.postScale(-1, 1);
mat.postTranslate(-radius, radius);
mat.postRotate((float)-Math.PI);
mat.postRotate(i * angle);
mat.postTranslate(radius, -radius);
matrix_bitmap = Bitmap.createBitmap(bm, 0, 0, (int)r.width(), (int)r.height(), mat, true);
}
fillShader = new BitmapShader(matrix_bitmap, Shader.TileMode.MIRROR, Shader.TileMode.MIRROR);
// Fill the triangle masked area with our image now
Paint fill = new Paint();
fill.setColor(0xFFFFFFFF);
fill.setStyle(Paint.Style.FILL);
fill.setShader(fillShader);
c.drawPath(triangle_mask, fill);
start_angle += angle;
}
kal.setImageBitmap(imageview_bitmap);
}
The output of the above function looks like so:
If anyone could provide some insight on how to properly do the image rotations/mirroring that would be greatly appreciated.

Okay I ended up going about this a different way. Instead of rotating the source image I simply draw the image mask to the same spot on the canvas, and then rotate the canvas itself. Let's say I have 12 image 'slices'. I draw 6 alternating segments, flip the canvas via canvas.scale(-1, 1) and then draw another 6 segments in where the blank spaces are. Here's the code I ended up with:
private Bitmap generateKaleidoscopeBitmap(float start_angle) {
Canvas canvas = new Canvas(imageview_bitmap);
canvas.drawColor(Color.BLACK);
BitmapShader fillShader;
Path triangle_mask = new Path();
RectF r = new RectF(0, 0, imageview_bitmap.getWidth(), imageview_bitmap.getHeight()); // create new rectangle to match the dimensions of our image
int centerX = imageview_bitmap.getWidth() / 2;
int centerY = imageview_bitmap.getHeight() / 2;
// how much to rotate the canvas by after the image is flipped
float offset = calculateCanvasSymmetryOffset(start_angle);
// Create a pie-slice shaped clipping mask
triangle_mask.moveTo(r.centerX(), r.centerY());
triangle_mask.arcTo(r, start_angle, angle);
triangle_mask.close();
// Fill the triangle masked area with our shader now
Paint fill = new Paint();
fill.setColor(0xFFFFFFFF);
fill.setStyle(Paint.Style.FILL);
fillShader = new BitmapShader(source_image, Shader.TileMode.MIRROR, Shader.TileMode.MIRROR);
fill.setShader(fillShader);
// Rotate the canvas and draw the clipping mask to the canvas
for (int i = 0; i < this.segments / 2; i++) {
canvas.drawPath(triangle_mask, fill);
canvas.rotate(angle * 2, centerX, centerY);
}
// mirror the canvas and rotate it once to counter the symmetrical offset
canvas.scale(-1, 1, centerX, centerY);
canvas.rotate(offset, centerX, centerY);
// Rotate the now mirrored canvas and draw the clipping mask to it
// This is a cheap and easy way of creating mirrored segments
for (int i = 0; i < this.segments / 2; i++) {
canvas.drawPath(triangle_mask, fill);
canvas.rotate(angle * 2, centerX, centerY);
}
return imageview_bitmap;
}

Change my mouse cursor to the polygon i click on in java

In my program in java, I have drawn these polygons in my JFrame and I want my mouse cursor to change to the one that I click on it, so by clicking again, the polygon will be drawn in the point of my click. I don't know how to do that since I don't know how to change my cursor to a polygon?

You want to create a custom cursor. The method to create and register that cursor is toolkit.createCustomCursor. Basically, create an image with an appropriate size, install it and use as needed. Here's a code snippet:
Toolkit kit = Toolkit.getDefaultToolkit();
Dimension dim = kit.getBestCursorSize(48, 48);
BufferedImage buffered = GraphicsUtilities.createCompatibleTranslucentImage(dim.width, dim.height);
Shape circle = new Ellipse2D.Float(0, 0, dim.width - 1, dim.height - 1);
Graphics2D g = buffered.createGraphics();
g.setColor(Color.BLUE);
g.draw(circle);
g.setColor(Color.RED);
int centerX = (dim.width - 1) /2;
int centerY = (dim.height - 1) / 2;
g.drawLine(centerX, 0, centerX, dim.height - 1);
g.drawLine(0, centerY, dim.height - 1, centerY);
g.dispose();
Cursor cursor = kit.createCustomCursor(buffered, new Point(centerX, centerY), "myCursor");