In Cocos2D I am creating my CCSprites with anchor points of (0,1) which is similar to the way UIKit does it. Anyway, I am trying to change the anchor point in Box2D, is this possible?
If so how would I do it with an anchor point of (0,1)?
Thanks!
Box2D bodies don't have an anchor point.
The anchorPoint is an offset of a node's texture relative to the node's position. Box2D bodies don't have a texture, hence no anchor point.
Generally speaking you're going to make a lot of things more difficult by changing the anchorPoint from its default 0.5,0.5 position. Like, for example, the issue that lead you to ask this very question.
Changing anchor point of shapes in body :
do a for loop to get the smallest x vertice and the biggest, substract to get the width, you can do in the same loop get smallest y vertice and the biggest and substract,
if you then move all vertices with the differences you will position the shape in the 0,0.
it works not sure if the best solution.
Related
I programmed a simple 2d app/ game.I just noticed, that an isometric scene instead of the 2d one would look gorgeous . I did not use any SpriteKit, etc. , it's just a simple single-view-app.
Now I draw some nice isometric vectors of e.g. a petrol station, which I would love to use instead of the plain 2D-images. For sure I can just use them as an imageview. But my idea was that I may animate driving cars in straight ways, so that they seem to be 3D (isometric), but are just images moving along a given path. What is the best way to do this? Can I use my isometric image as a Gamescene (never used)?
Greetings!
If you’ve been doing without SpriteKit so far, I don’t see any need to use it now. Keep them as UIImageViews, and animate their positions normally, just make sure that the point you move them to makes sense, so as not to break the illusion.
You can open up your image in Preview, click and drag along it’s direction to make a rectangular selection along that direction, and use the width and height of that box to make a ratio, like 20:25, which then simplifies to 4:5. Meaning for every 4 points it moves along x-axis, it should move 5 points along y-axis. Then store this ratio as a CGPoint somewhere in your code, note that all your isometric images should give you this same ratio.
Then you could make an abstraction that moves an imageview x points along its direction, using that ratio. Say you want to move it 100 points along its direction, and say the ratio is 4:5. The ratio is a triangle of width 4, height 5. You use a^2=b^2+c^2 to calculate the hypotenuse of that triangle. Then find a k such that ck=100. Then multiply a and b by that k to give you your delta x and delta y. Apply those deltas to its current position and you have the final position to animate to, which will be 100 points along its direction.
I'm not sure of my understanding of ARCore's anchor and planes.
For my application, I'm trying to get the floor coordinate frame, so I wait for a plane, the lower one, and get this plane's center pose as new center of the world.
Should I create an anchor ?
What could be the difference between tracking a plane or a anchor ?
Thanks.
What I have found works best is to create an Anchor to handle the x,z location of interest. For the y coordinate use the plane (or an offset from the plane).
The reasoning behind this is the center of the plan will move as a the understanding of the plane increases and the plane expands. Moving up and down, is good - since you want the plane in your case to be the floor. But since you are setting an origin point fixed in space you probably don't want to jump around left and right, nor forward and backward, so using an anchor for those will be better than the center point of the plane.
Is there any way to set an x,y coordinate that gravity pulls towards?
We want to suck a number of objects with physicsbodies towards a point as if it was a black hole.
Not for the regular world gravity.
To achieve this effect, you have to apply to each body an impulse every frame. The strength and direction of the impulse depends on the distance of the body (node) to the gravity source's position.
I am creating a spritenode, setting its position and changing its anchorpoint to (0, .5) and then creating a phyicsbody.
The physicsbody thinks my anchorpoint is still at (.5, .5), stupidly.
The same problem is referenced here, but unsolved: Physicsbody doesn't adhere to node's anchor point
The order I am doing things in is correct, it's just my physicsbody is stubborn.
The anchorPoint determines where the node's texture is drawn relative to the node's position. It simply does not affect physics bodies because it's a purely visual property (a texture offset).
For physics-driven nodes it is actually counter-productive to change the anchorPoint from its default because that will change the point around which the texture will rotate. And the physics body will usually also change the node's rotation.
So even if you were to move the physics body shape's vertices to match the sprite with a modified anchorPoint, the physics shape will be misaligned with the image as soon as the body starts rotating. And it'll seem to behave weird.
Plus whatever you want to achieve using anchorPoint you can more flexibly achieve by using the node hierarchy to your advantage. Use a SKNode as the physics node, and add a non-physics sprite node as child to that node and offset it the way you wanted the image to be offset by changing the sprite's anchorPoint.
You end up having two nodes, one invisible representing the physics body and one (or more) sprite(s) representing the visuals for the body but not necessarily tied to the body's center position.
I am just starting out in XNA and have a question about rotation. When you multiply a vector by a rotation matrix in XNA, it goes counter-clockwise. This I understand.
However, let me give you an example of what I don't get. Let's say I load a random art asset into the pipeline. I then create some variable to increment every frame by 2 radians when the update method runs(testRot += 0.034906585f). The main thing of my confusion is, the asset rotates clockwise in this screen space. This confuses me as a rotation matrix will rotate a vector counter-clockwise.
One other thing, when I specify where my position vector is, as well as my origin, I understand that I am rotating about the origin. Am I to assume that there are perpendicular axis passing through this asset's origin as well? If so, where does rotation start from? In other words, am I starting rotation from the top of the Y-axis or the x-axis?
The XNA SpriteBatch works in Client Space. Where "up" is Y-, not Y+ (as in Cartesian space, projection space, and what most people usually select for their world space). This makes the rotation appear as clockwise (not counter-clockwise as it would in Cartesian space). The actual coordinates the rotation is producing are the same.
Rotations are relative, so they don't really "start" from any specified position.
If you are using maths functions like sin or cos or atan2, then absolute angles always start from the X+ axis as zero radians, and the positive rotation direction rotates towards Y+.
The order of operations of SpriteBatch looks something like this:
Sprite starts as a quad with the top-left corner at (0,0), its size being the same as its texture size (or SourceRectangle).
Translate the sprite back by its origin (thus placing its origin at (0,0)).
Scale the sprite
Rotate the sprite
Translate the sprite by its position
Apply the matrix from SpriteBatch.Begin
This places the sprite in Client Space.
Finally a matrix is applied to each batch to transform that Client Space into the Projection Space used by the GPU. (Projection space is from (-1,-1) at the bottom left of the viewport, to (1,1) in the top right.)
Since you are new to XNA, allow me to introduce a library that will greatly help you out while you learn. It is called XNA Debug Terminal and is an open source project that allows you to run arbitrary code during runtime. So you can see if your variables have the value you expect. All this happens in a terminal display on top of your game and without pausing your game. It can be downloaded at http://www.protohacks.net/xna_debug_terminal
It is free and very easy to setup so you really have nothing to lose.