Drawing an image rotated in the direction of movement | Graphics | Graphics2D

Question

Drawing an image rotated in the direction of movement | Graphics | Graphics2D

It is necessary to draw the image rotated in the direction of movement (the rotation should be relative to the center of the image):

Example:

I know the speed of x and y, and the position of the image(x,y), and the size of the image(width and height), as well as the size of the field on which I draw

I tried this way:

Graphics2D g = (Graphics2D) gr;
g.rotate(Math.toRadians(Math.atan(vx/vy))); // vx,vy - скорость по x и y
g.fillRect((int)(x-w/2), (int) (y-h/2), w, h); // Это я потом заменю на картинку

But the image is NOT rotated relative to the center and the rotation is incorrect

Details:

I draw on JPanel in the method paint(Graphics gr)
Using Graphics2D

1

java математика swing геометрия

Author: Roman C, 2021-01-20

Source

1 answers

score 2 · Accepted Answer

Math.atan requires the relation y/x, but this is not so important, because see below
Math.atan you need to replace it with Math.atan2(vy, vx) to get the angle in the entire range
The result Math.atan/atan2 is already in radians, no need to convert yet if rotate requires radians

For rotation relative to a certain point (cx, cy), the affine transformation matrix is constructed as follows:

перенос на (-cx, -cy)
поворот
перенос на (cx, cy)

In Graphics2D I see an overlap for this method:

rotate(double theta,  double x,  double y)