Hello I am making a game in java. I am using a collection of lines to represent a shape to detect collisions. I need to be able to rotate this shape by degrees or radians
As you can see from the diagram above the shape is a collection of line segments with 2 points a and b. I need to know how would I rotate all of lines together and still retain the shape.
Sounds like a job for AffineTransform (assuming you're doing 2D)
Something to this effect:
Point2D rotatedPoints = new Point2D[yourPoints.length];
AffineTransform at = new AffineTransform();
at.rotate(Math.toRadians(yourDegreeRotation), xToRotateAround, yToRotateAround);
at.transform(yourPoints, 0, rotatedPoints, 0, yourPoints.length);
Related
How can I make the vertices of a polygon in libgdx?
I am trying to make a pentagon for collision detection and I am kind of confused about how the vertices part is done, until now I used rectangle to achieve this
You should make several polygons since a pentagon is a convex shape and not easy to compute if a point is within the shape.
To create a shape with the Polygon class you specify the vertices with a float array. In sequence, you specify the x and y positions. Since Polygon is a 2D shape in Libgdx the Z axis is not needed.
Below is a polygon for a triangle shape, create your pentagon like this from multiple polygons and use Intersector to test the polygon vs various other geometry like lines and points. Note, Intersector does contain method overlapConvexPolygon but I am pretty sure that gives true for something in between the points of your pentagon.
new Polygon(new Array[
0, 0,
10, 0,
5, 10
]);
I am creating a small java 2D game and i want to know if there is any way to rotate AWT rectangle
AffineTransform origXform = g2d.getTransform();
AffineTransform newXform = (AffineTransform) origXform.clone();
newXform.rotate(angle, pivotX, pivotY); // pivotX ,pivotY is the starting
point of the hand image
g2d.setTransform(newXform);
Rectangle arm = new Rectangle(bowX + 5, bowY + 55, 60, 5);
g2d.drawImage(playerBowReadyImg, bowX, bowY, null); //hand image
on the above code i simply draw the hand image which rotates based on the mouse position, i also set the rectangle on the hand but the problem is rectangle is not rotating along with the hand image.
also i am not using rectangle for any drawing purpose but to detect the collision.
however using g2d.draw(arm); draws the rotated rectangle but it not actually rotate the rectangle it just draws the rotated one.
any suggestion is appreciated.
Ok my question is marked as duplicate so i tried the answers i find there but the code i get only rotate my rectangle for the draw purpose only.
Image to depict the problem
now to be more specific the arrow in the image can only detect the collision for the blue rectangle (the original position) instead of the red one (rotated rectangle).
again i don't want to actually draw the rectangle but want to detect the collision when the arrow collide with the rectangle.
See AffineTransform.createTransformedShape(Shape) which:
Returns a new Shape object defined by the geometry of the specified Shape after it has been transformed by this transform.
I'm wondering if there is a way to create a shape fixture in Java 2D.
More specifically, I'm trying to be able to draw a predefined shape at different locations with different colors.
I know you can use the fill(shape) methods to draw shapes.
However, this seems to require creating a new shape at the coordinate that I want to draw it.
Is there any way to reuse the same shape each time? Or do I have to create a new shape for each location.
You can do this by translating the transformation matrix of the graphics object.
Let's say you have a Shape called shape whose coordinates are relative to the center of the Shape. You also have an instance of Graphics2D called g2.
Now you code could look something like this:
// Set the color of the Shape.
g2.setColor(Color.BLACK);
// Backup the transformation matrix so we can restore it later.
AffineTransform backupTransform = new AffineTransform(g2.getTransform());
// Translate everything that is drawn afterwards by the given coordinates.
// (This will be the new position of the center of the Shape)
g2.translate(53, 27);
// Draw the Shape.
g2.draw(shape);
// Restore the old transform, so that things drawn after this line
// are not affected by the translation.
g2.setTransform(backupTransform);
I am attempting to render an ellipse using ShapeRenderer, and have come up with the following partial solution:
void drawEllipse(float x, float y, float width, float height) {
float r = (width / 2);
ShapeRenderer renderer = new ShapeRenderer();
renderer.setProjectionMatrix(/* camera matrix */);
renderer.begin(ShapeType.Circle);
renderer.scale(1f, (height / width), 1f);
renderer.circle(x + r, y, r);
renderer.identity();
renderer.end();
}
This draws an ellipse at the specified coordinates with the correct width and height; however, it appears that the scale transformation causes the circle to be translated in the viewport, and I have not been successful in determining the mathematics behind the translation. I am using an orthogonal projection with y-up where the coordinates map to a pixel on the screen. I am not very familiar with OpenGL.
How can I draw an ellipse using libgdx, and have it draw the ellipse at the exact coordinates I specify? Ideally, that would mean that the origin of the ellipse is located in the top-left corner, if the ellipse was contained in a rectangle.
The new Libgdx ShapeRenderer API (current nightlies, in whatever release will come after v0.9.8) contains an ellipse drawing method so you can ignore the rest of this answer. The ShapeRenderer method has changed in other ways, too though (e.g., the ShapeType is just Filled, Line, or Point now).
For folks stuck with the older API, you should be able to work-around the distortion by making sure the scaling happens around the origin. This is a standard OpenGL practice (so its a bit obtuse, but they're following OpenGL's lead). See Opengl order of matrix transformations and OpenGL: scale then translate? and how?. Even better (again standard OpenGL practice) you end up listing the operations in the reverse order you want them to happen at, so to make a circle, distort it into an ellipse, then move it to a specific destination you actually write code like:
renderer.begin(ShapeType.Circle);
renderer.translate(x, y, 0);
renderer.scale(1f, (height/width), 1f);
renderer.circle(0, 0, r);
renderer.end();
I have a Graphics2D object which I use to draw on my Canvas. I draw multiple shapes on the Canvas and want to transform only one (or part) of them.
I'll try to keep this simple:
void render(Graphics2D g) {
... // Draw shape 1
... // Draw shape 2
... // Draw shape 3
}
How would I go about rotating shape 2 while leaving shape 1 and 3 intact? By "rotate" I mean rotating around its center point, which we can define as x and y for example.
I've been looking for a way to do this for a while now, but couldn't find anything that works the way I want it to.
Is there any simple way to do this?
Rather than rotating the shape around it's centre point, rotate and then translate the canvas. To rotate around the centre of the shape at (x, y), first translate the canvas by (-x, -y) and then rotate the canvas -d degrees and draw the shape as normal at (0,0).
When you're done, rotate back then translate back (note that with these geometric transformations the order is important, translating and then rotating will give you a completely different outcome).
This means that you can still draw an object at any rotation without having to recalculate the coordinates yourself.
AffineTransform afx = new AffineTransform();
afx.rotate(angleRad, s.getCenter().x, s.getCenter().y);
//afx.rotate(angleRad);
java.awt.Shape ss = afx.createTransformedShape(s.getPrimativeShape());
return ss;
s is my wrapper class for java.awt.Shape and does some stuff with it.... But what you want is in line 2.
afx.rotate(Angle,xAnchorPoint,yAnchorPoint);
afx.rotate rotates the object about the point (xAnchorPoint;yAnchorPoint).
Hope this is what you wanted
In order to rotate a shape, use one of the Graphics2D.rotate methods.
Cache the transform used for both shape 1 and shape 3. Before drawing shape 3, ensure that you reset the transform to the cached one, since using rotate for shape 2 will alter the current transform coordinates.
Steps:
Cache current transform
Draw shape 1
Rotate
Draw shape 2
Set transform to cached one
Draw shape 3