I am stumped on working out the angle of reflection in my AS3 project, I have the formula but the formula relies on you knowing the angle of the object that is reflected against (to work out the perpendicular angle) the trouble is the objects are all at 0 rotation but are shaped differently (e.g the four sides of the stage have a line across them which is at 0 rotation but some are horizontal and some vertical).
How would I work out the angle of reflection purely from the angle of the object that is being reflected, taking into account AS3 returns rotation values between -180 and 180.
Anyone got an idea?
This doesn't answer my question so much as it only works on objects reflecting of horizontal or vertical objects but this function will get you the angle of reflection based upon the rotation of the object which is being reflected...
var reflection:int = (incidence > 0) ? 180 - incidence: -180 - incidence;
where incidence which is the rotation of the object which is being reflected.
Related
I try to use 2 ellipses to detect a collision if they overlap. I have to rotate the ellipses but I can't figure out how this works. I'm working with the "com.badlogic.gdx.math.Ellipse" class but it seems to have no method for rotating. Any ideas? Thx in advance!!
Unfortunately, LibGDX doesn't have in-built rotating functions for ellipses.
Instead, I'd either be resorting to a circle in which rotation does not matter, or use polygons to check intersection.
Polygons are formed through an array of float values (vertices), where, every even element of the array is the horizontal component (x) and the odd, the vertical component (y).
Polygon polygon1 = new Polygon(vertexSet1);
Polygon polygon2 = new Polygon(vertexSet2);
Then, by using an Intersector, you can then check whether these polygons have intersected. The more vertices, the more accurate your shape will be. Just remember to have 6 or more elements in your vertex array, as the 6 floats will give 3 (x, y) points which is the minimum required for a polygon.
if (intersector.overlapConvexPolygons(polygon1, polygon2) {
//do your intersection code
}
The polygons themselves have commands to translate, scale and rotate, allowing for the rotations you mentioned above.
This may be an issue that I simply do no know the proper terminology to research the answer to this, I am pretty sure the solution is a function of trig.
I have a method which accepts an X/Y position coordinate and an angle in degrees. It should return an updated X/Y based on the rotation angle provided.
For example, A point is usually located at x=0,y=2 (top middle). Now I need to rotate it to it's side by 90 degrees. In my mind I know it's location is now x=2,y=0 (middle right) but I do not know the equation to produce this.
I think I need to first determine the quadrant of the starting point, and then perform the proper trig function from there. This is for a game I am developing using libgdx which is where the Vector2 object comes from.
I have come this far:
public Vector2 getPointsRotated(Vector2 startPoint, float angle){
Vector2 newPoint = new Vector2(0,0);
// determine the starting quadrant
int quad=0;
if((startPoint.x>=0)&&(startPoint.y>=0)){quad=0;}
if((startPoint.x<0)&&(startPoint.y>=0)){quad=1;}
if((startPoint.x<0)&&(startPoint.y<0)){quad=2;}
if((startPoint.x>=0)&&(startPoint.y<0)){quad=3;}
if(quad==0){
// doesn't work
newPoint.x = (float) ((newPoint.x)* (Math.sin(angle)));
newPoint.y = (float) ((newPoint.y)* (Math.cos(angle)));
}
// ...
// other quadrants also don't work
// ...
return newPoint;
}
Thanks for any help.
Update:
I have been avoiding and returning to this problem for a few days. Now after finally posting the question here I figure it out within minutes (for ppl using libgdx anyway).
Libgdx provides a rotate function for Vector2s
so something like:
Vector2 position = new Vector2(0,2);
position.rotate(angle);
works perfectly.
I find rotation matrices are very helpful for this sort of problem.
https://gamedev.stackexchange.com/questions/54299/tetris-rotations-using-linear-algebra-rotation-matrices
I'm not very good with radial calculations, I can't imagine thus I can't be sure. I need some explanation of Math.atan2() thing, please.
Usual task - to make an object rotate after the mouse. I get the differences, get the angle, I see angles in the text areas and DIRECTLY the object does follow the mouse. What I need now is everything to be smooth. I need angles to be 0-360 but after 180 object rotation becomes -180 and counts backwards, and mouse rotation becomes -90 after 270 and also counts back to 0.
More deeply, I want a smooth rotation, it means a set speed of say 2 per frame, to meet the mouse angle the shortest way. It takes to set conditions and I can't do that cause I don't even understand the logic of these values. They are almost random! I don't need it to be done or copied, I need to understand to move on so if you could please explain how does it work and what I do wrong...
Code is simple:
angle = Math.atan2(deltaY,deltaX)/(Math.PI/180) + 90; //+90 cause it lacks it to look at the mouse//
Object01.rotation = angle;
So the problem is I don't even get how it works... if 2 values are different the object can't point at the mouse but it does. Numbers lie and if I need something based on these numbers it will be wrong. Very wrong... Need organization. Meaning I want everything to be ready for further coding that will be based on the rotations to not jump up and down cause of misfit ends.
Add: Explanation of how does it happen, what I described above. Why such a chaos of the values? And an advice on how could I arrange it for further coding, just as I said. Animation alone wont work if I want to make rotation an element of important events such as shooting direction and aiming speed. Or changes of speed rotation of a lockpicked lock. Or anything much more complicated that wont work if I don't make straight and clear values: from A to Z, from 1 to 10, no 8s between 2 and 3, no R before B, no mouse angle 270 when object facing it -90 when they both started from 0 and reached 180 together.
Oh, and as I said, mouse facing works but when I try to make a certain speed of chasing mouse the shortest way it turns the object wrong directions in all 4 quarters. I assume it's also about this arctangens thing that has issues with delta values becoming negative in different quarters. And when I change it, some other value goes wrong... So I need to know exactly what I'm doing to know what's wrong and how to fix it. So yep. Need explanation. Please.
Add2: angleZ = Math.atan2(oppSide,adjSide)/(Math.PI/180);
So I divided rotation to 4 quarters, for each I count atan as opp. side to adj. side, then add 90, 180 and 270 respectively. My mouse rotation does 360, but the object that follow through simple object.rotation = angleZ; still goes to 180, then from -180 to 0 on the left side. Why does it ignore the simple command? The rotation fits but I need it to be equal, no surprises! Why is it happening? How can a number I directly set to be equal to another number as a base of the action change itself to the one of same rotation but completely different number? It doesn't even know it's degrees! It's as simple as "object.rotation, please be equal to the number I choose!"
It's just different coordinate systems. Like how x starts at 0 at the left of the stage, goes +x to the right, and -x to the left, object rotation starts at 0˚ pointing up, and goes +180˚ clockwise and -180˚ anti-clockwise.
Math.atan2 happens to start at 0 pointing left (-x), and go +270˚ clockwise and -90˚ anti-clockwise, which is annoying, but it just means you have to convert between coordinate systems by adding 90˚.
You can spin something around over and over of course, so the numbers jump so that they always stay within the same range, because 361˚ is the same as 1˚, and -270˚ is the same as 90˚. You can tell an object to rotate outside of the -180˚ to 180˚ range, and it will normalise the rotation to within those values.
As mitim described, to smoothly animate rotation you'll either need to use Event.ENTER_FRAME, a Timer, or a tweening library like TweenLite. Most tweening libraries can work out the shortest rotation direction for you, but otherwise you can simply calculate both and see which is smaller.
As an idea, since it seems like you know the angle you need to rotate towards and it's direction, would it be easier to just animate towards that angle to get your smooth rotation? Basically treat it like any other animatable property and just add on your rotation speed (2 degrees it looks like) per frame tick, until it reaches the desired rotation.
Find angle amount needed to rotate by
Figure out if clockwise or counter clockwise direction and set the rotation amount. This can be figured out by checking if the angle is great then 180 / positive or negative
Add the rotation amount * direction every frame tick, until the desired rotation is less then or equal to the rotation amount per frame
Set rotation to desired rotation
I am trying to make a donut chart using the arc function in the HTML5 canvas. I am wanting to know how to use the lineTo function to connect two arcs together.
At the moment I have a pie chart which has fixed central x/y coords, so making the slices is easy as once the arc of each slice is done, the lineTo method simply uses the the fixed coords.
However with a ring/donut chart, I have two arcs, one with a smaller radius, but no idea how to connect the ends together without horrifically complicated trigonometry. Is there any way to get the 'start' and 'end' x/y coords of the arc?
I have a current hackyish 'solution' of simply drawing a smaller white circle over the pie chart to give the ring graph, but I want to know the answer to the question above.
You just have to remember a little trigonometry. If your center point is x, y and radius is r; then the coordinates on the circle at an angle alpha are:
pointX = x + Math.cos(alpha) * r;
pointY = y + Math.sin(alpha) * r;
And you have two of those angles, corresponding to the starting and the ending point.
Why are you drawing arcs? Would'nt it be easier if you just draw the circle (or circles for the ring) and then draw radius?
I have a papervision3d sphere primitive that I am adding to a scene. The sphere is being sized with a radius of 285. However, because of my camera properties (zoom, focus and z) the sphere is rendering at 206px instead of 570px which is what I want (2 * radius).
A while back I found a blog post concerning this very issue and it was explained that you can set the z of any object in the scene to appear in 3D space the same size it would appear in 2D space by using the following:
mySphere.z = (this.camera.zoom * this.camera.focus) - Math.abs(this.camera.z) + radius;
The above worked when I was using several blocks, where radius was replaced with width/2. For some reason this does not work for the sphere.
Any ideas, pointers on how to get a sphere with a 570px diameter to show up on screen?
Thanks.
This cannot be achieved, at least not precisely. The perspective projection does not map a sphere to a circle. See how the spheres at the edges of this image are getting deformed?
(source: uni-stuttgart.de)