Ok I've been trying to rotate a Rectangle that sits on top of an image. I have a Scrollable class that displays the Image. I can draw Rectangles on top of the Image. My problem is trying to rotate the Rectangles when the Image is rotated. The Rectangle gets lost and placed in the wrong location.
I've already tried suing Graphics2D, AffineTransform, createTransformedShape() but no luck.
What I'm trying to do now is to rotate the Rectangle manually. I'm trying to get the Rectangle Point(x,y) using below formula:
double rectX = (Math.cos(Math.toRadians(90)) * (x - anchorX) - Math.sin(Math.toRadians(90)) * (y - anchorY)) + anchorY;
double rectY = (Math.sin(Math.toRadians(90)) * (x - anchorX) - Math.cos(Math.toRadians(90)) * (y - anchorY)) + anchorY;
How can I find the anchorX and anchorY values using Java? I've tried diving the Image height by 2 but doesn't work for all rotation angles. Do I have to get the JPanel width and height or something? Is there a formula that Java uses to find anchor points?
I'm not sure of the goal, but I see two possible alternative approaches:
Use an inverse transform, as shown here.
Render the upright image and rectangle(s) into a BufferedImage and rotate the composite image, as shown here.
If you're trying to make it like a a box rolling across the top, you have to find the bottom corner in direction of travel. If you're rolling to the right, you need the bottom right corner.
Related
Firstly, I am trying to make a simple game in Java. I have a viewport that shows a tile map and I have a tank in the middle that moves by controlling the JScrollBars of the scrollpane in which the viewport resides in. So far everything has been going well, until I needed to rotate an image. Here is a picture of the game: Note: the tank body and tilemap are on seperate panels and do not share the same graphics.
Picture of non rotated tank body:
Essentially, I want to rotate a buffered image around its center (rotating in place) using arrow keys. I already have the code for the keys, and I also have a method to try and rotate the buffered image given a buffered image and angle in degrees (the angle is changed to radians in the method). This method will return a buffered image that is rotated correctly. Here is the code:
public static BufferedImage rotateImage(BufferedImage image, double angle) {
if(angle == 0)
return image;
else {
angle = Math.toRadians(angle);
double x = Math.abs(Math.cos(angle));
double y = Math.abs(Math.sin(angle));
int newWidth = (int) Math.floor(image.getWidth()*x + image.getHeight()*y);
int newHeight = (int) Math.floor(image.getHeight()*x + image.getWidth()*y);
BufferedImage rotated = new BufferedImage(newWidth, newHeight, image.getType());
Graphics2D tool = rotated.createGraphics();
AffineTransform transformer = new AffineTransform();
transformer.rotate(angle, image.getWidth()/2, image.getHeight()/2);
tool.drawImage(image, transformer, null);
tool.dispose();
return rotated;
}
}
However, as the title suggests, the image gets cut off at the top and left sides of the image when rotated as shown:
Picture of rotated tank body:
So I have looked at many different forums but I could not solve my problem. I could add whitespace around the image, but that interferes a lot with collision detection which I plan to do later on. I know that it has to do something with the original display being smaller than the display of the rotated image, and I have tried to translate accordingly in many ways. If I translate with this line of code specifically,
transformer.translate((newWidth - image.getWidth())/2, (newHeight - image.getHeight())/2);
Then the image (tank body) rotates without cutting, but bounces out of place as shown (I drew a rectangle to show where it was):
Picture of rotated tank with translation:
I also have tried negating the translations too but it only avails to funky movements.
So, I really have no clue how to solve this, and I have been spending too much time on this problem. I would really appreciate a helpful answer that directly edits my method if possible.
Answer
So here is the opening idea that I needed to realize to answer this problem.
The method to translate and rotate is meant so that the image is not cut off. However, it won't be around the center as intended as seen in the 3rd picture. But again, the method is not intended to recenter it. The painting code itself needs to account for this shift. I simply added variables to account for this:
xOffset = (newWidth - image.getWidth())/2;
yOffset = (newHeight - image.getHeight())/2
And simply subtracted these from where I was painting the tank's body.
Thanks to #camickr for the solution
When rotating a square sprite around the center point, the target image should be larger than the original image by a factor of the square root of 2 (approx. 1.41). For example, a sprite will not be clipped at a rotation angle of 45 °.
I hope this information helps you to solve your problem.
I am facing a similar problem to this question however I'm trying to use java: AS3 - How to find the position of an object relative to the stage?
I'm drawing a rectangle to the screen. I'm using g.translate and g.rotate to scroll and rotate the screen. The x and y variables I am using to position the rectangle therefore do not depict where the rectangle is on the actual screen. Sorry if I haven't explained it well
I tried to post a different topic for this but people didn't really seem to understand what I was trying to do, so, now I've closed that one and opened this one to give more detail and rephrase the question as a whole.
Ok.
So basically, I have an application which draws an Ellipse. Now, I have a certain number of points (that can be random) in which I have to rotate an image and draw at.
Using Maths I know that to get a point on an Ellipse based by using an angle I use the following equation;
final int radiusW = (width / 2);
final int radiusH = (height / 2);
final int angle = 120;
int pointX = (int) (radiusW + (radiusW * Math.cos(Math.toRadians(angle))));
int pointY = (int) (radiusH + (radiusH * Math.sin(Math.toRadians(angle))));
And that works fine, I can locate an absolute point around the perimeter of the Ellipse.
However, now I'm trying to draw an image on this point so that the image is rotated facing the center of ellipse and is centered on the point.
So, to get the image rotated to the center of the point I do the following;
final AffineTransform at = new AffineTransform();
at.rotate(Math.toRadians(angle - 90), image.getWidth() / 2, image.getHeight() / 2);
final AffineTransformOp ato = new AffineTransformOp(at, AffineTransformOp.TYPE_BILINEAR);
And then I get my new rotated BufferedImage using;
BufferedImage rotated = ato.filter(image, null);
However, I can't seem to be able to get the central point of the image anymore.
If the angle was 0 so that the Image was the original direction then I would simply do;
graphics.drawImage(rotated, pointX - rotated.getWidth() / 2, pointY - rotated.getHeight() / 2, this);
However I'm not sure how to find the central point and draw it based upon that on a rotated image.
I know it involves using cos and sin to multiply the original pointX and pointY by the rotation matrix but everytime I try and work out a solution it always draws completely wrong.
Any help would be very much appreciated as I've spent the best part of a day trying to resolve this.
Thank you.
The thing is that if you just use sin and cos to rotate the corner of the image you will end up with the new rotated position of that corner - when actually what you want to find is the new width and height.
The center is width/2, height/2
Use this to calculate your new width and height:
Calculate Bounding box coordinates from a rotated rectangle
I have done this with OpenCV, and there the image have been rotated but the resulted image was having the same width and height as the initial on. The image was cropped if it was getting out of the initial dimentions and there were black pixels if no information (the rotated image has no pixels in that place).
If you think that rotated has more pixels than the initial image you can verify with size() or length(). Or you can play with the diagonals of the initial rectangle (image size): compute the projection of the diagonals and thake the greatest or what you think. But I am sure that it is similar to the OpenCV case.
I don't know if this can help you, but I hope so.
Your question is not entirely clear but it seems to me that you have a misunderstanding of the nature of the angle used to parametrise your ellipse. The angle as you have it is merely used to parametrise the form of an ellipse equation. It is not the same as the polar angle (except at particular angles). That is to say if you evaluate a point on your ellipse using an angle of (pi/4) radians (45 degrees), then measured the angle that the line from the ellipse centre to your point makes with the axis, it will not measure 45 degrees (except for the case where the ellipse is actually a circle).
That is to say that
int pointX = (int) (radiusW + (radiusW * Math.cos(Math.toRadians(angle))));
int pointY = (int) (radiusH + (radiusH * Math.sin(Math.toRadians(angle))));
is just a parametrisation of an ellipse and that angle is not a polar angle and treating this angle as a rotation angle will not give accurate results (except at integer multiples of (pi/2) radians)
It seems to me that you require the polar form of an ellipse relative to its centre in order for your code to make sense in the context of using this angle for rotation.
It is also possible that I have misunderstood your question though, in which case this answer will be downvoted on a grand scale and I will delete it.
I'm trying to properly configure my Camera and Sprites in libGDX to show up in a 2D coordinate system properly with the origin at the bottom left hand corner.
I set up my Camera like this:
cameraWidth = Gdx.graphics.getWidth();
cameraHeight = Gdx.graphics.getHeight();
camera = new OrthographicCamera(1, cameraHeight/cameraWidth);
And I set up my Sprites like this:
sprite.setOrigin(sprite.getWidth()/2, sprite.getHeight()/2);
sprite.setScale(scale);
sprite.setPosition(startX,startY);
My problem is with sprite.setSize(x,y). If I set all the sprites to have a size of (1, texture aspect ratio), then everything draws with the right display ratio (not smushed or stretched), but nothing draws in the correct place. For example, if I draw something at (0,0), it will draw with its bottom left corner off the left side of the screen and up a number of pixels.
I've noticed by changing around the ratio I can get things to draw in different places - namely if I set it to (1, display aspect ratio) things look pretty close to drawing in the right place - they just draw from their center, not their bottom left corner, as LibGDX specifies. The only problem is that the images all appear as smushed or stretched, which is no good.
This seems like a simple problem and I just want to know how to set this up so I can have a sensible coordinate system that draws things in the right place and in the right aspect ratio. Thanks.
Once you change your viewport to match the screen's aspect ratio then (0, 0) will no longer be at the bottom left of the screen unless the screen is square. If the screen is wider than it is high then the visible portion of the x axis will still go from 0.0 to 1.0, but 0.0 on the y axis will now be somewhere off the bottom of the screen.
If you adjust the camera so that (0, 0) is at the bottom left of the screen, and remember that the visible y axis will only go up to grapicsHeight / graphicsWidth then that should solve your coordinate problem.
I would recommend setting the camera to point to the middle of the screen rather than the bottom left. There's an example here that does exactly that, drawing a 2:1 rectangle which is always in the centre of the screen, always with a 2:1 ratio no matter how much you resize it.
I've found a solution to this problem:
Set the camera to ortho (even though it's already an orthographic camera)
camera.setToOrtho(false,1,screen height / screen width);
Also, each sprite must have its position set to (x - sprite.getWidth()/2, y - sprite.getHeight()/2. I extended the Sprite class and overrode the setPosition method to account for this. Now, every time the position is set, the Sprites end up going where you "would think they'd go", with setPosition(0,0) putting it in the bottom left and setPosition(1,height/width) in the top left.
Oddly enough, this draws every sprite centered around the (x,y) point, which would make sense since width/2 and height/2 were subtracted from the position, except not subtracting the values does not make setPosition center the sprite via the bottom left corner - it's centered in a way I haven't figured out.
My image is of size 720x480 and stage is of same size. The boolean parameter, whether to stretch the stage or not is kept false, so that aspect ratio is maintained, now the problem i am getting that a black area is shown on either side of the screen I want my scene to be centered. The link below refers a file, which shows the problem more clearly, that image is aligned to the bottom left i want it to be centered so that the black area is divided equally on top and the bottom.
what is the approach to solve this?
http://badlogicgames.com/forum/viewtopic.php?f=11&t=3398
You have to specify X and Y coordinate as the following way
X = (Gdx.graphics.getWidth() - sprite.getRegionWidth()) / 2.0f;
Y = (Gdx.graphics.getHeight() - sprite.getRegionHeight()) / 2.0f, sprite.getRegionWidth()/2.0f;
You have to calaculate center of the image. Using this way you can put your image in center of the screen. Also here I user Sprite to display image.