I have a single cloud texture that I want to displace arbitrarily along the Y ("vertical") axis of a SCNNode spherical geometry, to give the illusion there are many different textures of clouds.
I read the docs about SCNMaterialProperty, CATransform3D rotation, but I'm completely lost. In a 3D program, you can set your texture "origin" along the X, Y and Z axis -- what is the equivalent in Scene Kit / Core Animation ?
Thanks for your help!
SCNMaterialProperty has a contentsTransform property that allows you to animate texture coordinates. You can also use shader modifiers if you want more control and depending on th effect you want to achieve.
In the Bananas sample code from WWDC 2014 this technique is used to animate the smoke emitted by the volcano in the background.
I finally ended up with this:
self.cloudNode.rotation = SCNVector4Make(0.0,
1.0,
0.0,
arc4random_uniform(360)*M_PI/180.0);
I'm not a maths genius anyway.
Related
I have a simple UIImageView in my view, but I can't seem to find any feature in Apple's documentation to change the UV Coordinates of this UIImageView, to convey my idea to you, this GIF file should preview how changing 4 vertices coordinates can change how the image gets viewed on the final UIImageView.
I tried to find a solution online too (other than documentation) and found none.
I use Swift.
You can achieve that very animation using UIView.transform or CALayer.transform. You'll need basic geometry to convert UV coordinates to a CGAffineTransform or CATransform3D.
I made an assumption that affine transform would suffice because in your animation the transform is affine (parallel lines stay parallel). In that case, 3 vertices are free -- the 4th one is constrained by the other 3.
If you have 3 vertices, you can compute the affine transform matrix using: Affine transformation algorithm
To achieve the infinite repeat, use UIImageResizingMode.Tile.
I want to create the same transforming effect on XNA 4 as Photoshop does:
Transform tool is used to scale, rotate, skew, and just distort the perspective of any graphic you’re working with in general
This is what all the things i want to do in XNA with any textures http://www.tutorial9.net/tutorials/photoshop-tutorials/using-transform-in-photoshop/
Skew: Skew transformations slant objects either vertically or horizontally.
Distort: Distort transformations allow you to stretch an image in ANY direction freely.
Perspective: The Perspective transformation allows you to add perspective to an object.
Warping an Object(Im interesting the most).
Hope you can help me with some tutorial or somwthing already made :D, iam think vertex has the solution but maybe.
Thanks.
Probably the easiest way to do this in XNA is to pass a Matrix to SpriteBatch.Begin. This is the overload you want to use: MSDN (the transformMatrix argument).
You can also do this with raw vertices, with an effect like BasicEffect by setting its World matrix. Or by setting vertex positions manually, perhaps transforming them with Vector3.Transform().
Most of the transformation matrices you want are provided by the Matrix.Create*() methods (MSDN). For example, CreateScale and CreateRotationZ.
There is no provided method for creating a skew matrix. It should be something like this:
Matrix skew = Matrix.Identity;
skew.M12 = (float)Math.Tan(MathHelper.ToRadians(36.87f));
(That is to skew by 36.87f degrees, which I pulled off this old answer of mine. You should be able to find the full maths for a skew matrix via Google.)
Remember that transformations happen around the origin of world space (0,0). If you want to, for example, scale around the centre of your sprite, you need to translate that sprite's centre to the origin, apply a scale, and then translate it back again. You can combine matrix transforms by multiplying them. This example (untested) will scale a 200x200 image around its centre:
Matrix myMatrix = Matrix.CreateTranslation(-100, -100, 0)
* Matrix.CreateScale(2f, 0.5f, 1f)
* Matrix.CreateTranslation(100, 100, 0);
Note: avoid scaling the Z axis to 0, even in 2D.
For perspective there is CreatePerspective. This creates a projection matrix, which is a specific kind of matrix for projecting a 3D scene onto a 2D display, so it is better used with vertices when setting (for example) BasicEffect.Projection. In this case you're best off doing proper 3D rendering.
For distort, just use vertices and place them manually wherever you need them.
I'm using XNA but it doesn't matter too much for this example. So let's say I have a sprite. I then apply a scaling matrix before anything. Is the scaling matrix applied scaling the local axis of the sprite or just moving the points down? In other words, is applying a scaling matrix of 0.5f in the world space to my sprite at the world origin scaling down the local axis of the sprite or just all the points that make up that sprite by half?
The same kind of applies to a translation and then scaling. In my head, I picture a translation matrix of 30,30 as moving the sprite's local origin to 30,30 and as a result, the sprite's local axis to 30,30. Then, scaling by 0.5f would scale back the local axis but I don't see why the origin of the sprite would now be at 15,15.
This confusion compounds the fact that is you perform a translation of 1 to the right on the x-axis in the world, you are now moving based on the scale which you applied (so you would only move .5 in the world). This leads me to believe that the scale is applied to the object's own axis.
Btw, if you guys talk about the origin in your followups, could you state which origin you are referring to?
Thanks
Normally a sprite is defined by it's vertices (points). Applying a scaling matrix to a sprite will transform the vertices (points) of the sprite.
A scale matrix always assumes (0, 0) is the origin of the scale transform. So if you scale a sprite centered at (30, 30) all points will stretch away from the (0, 0) point. If it helps, imagine the sprite as a small dot on a circle around the (0, 0) point with that entire circle being scaled.
If you want to scale a sprite at (30, 30) from the center of the sprite, you have to translate the center of the sprite to (0, 0) first, then translate the sprite back out to (30, 30) after the scale has been performed.
So that would be:
Translate(-30, -30)
Scale(0.5)
Translate(30, 30)
To expand on Empyrean's answer, 3D worlds usually have at least four coordinate systems, each with its own local origin:
Object Space
World Space
Camera Space
View Space (2D!)
with three transformations:
Object to World
World to Camera
Camera to View
You can create new coordinate systems, for example 'Model Space', with the transformation 'Model to Object'. Using this, you get a series of steps:
Model -> scale -> Object
Object -> rotate -> translate -> World
World -> rotate -> translate -> Camera
Camera -> perspective -> View
In OpenGL you would push the matrices in the reverse order listed above, so the Model->Object transformation is the last to be pushed, and OpenGL should render the object correctly. I would assume XNA / DirectX has a similar system.
Getting more complex, Model Space can have a hierarchy of translations, scales and rotations in a tree to produce a skeletal system which can then be used to deform the model mesh. This is usually called Skinning.
So, to answer the question, depending on which transformation you apply a rotation transformation, for example, you will get different results. In the Model->Object transformation, the model will rotate about the object's origin. In the Object->World transformation, the object will rotate about the world's origin.
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.
I have a sprite object in XNA.
It has a size, position and rotation.
How to translate a point from the screen coordinates to the sprite coordinates ?
Thanks,
SW
You need to calculate the transform matrix for your sprite, invert that (so the transform now goes from world space -> local space) and transform the mouse position by the inverted matrix.
Matrix transform = Matrix.CreateScale(scale) * Matrix.CreateRotationZ(rotation) * Matrix.CreateTranslation(translation);
Matrix inverseTransform = Matrix.Invert(transform);
Vector3 transformedMousePosition = Vector3.Transform(mousePosition, inverseTransform);
You might find the following XNA picking sample useful:
http://creators.xna.com/en-us/sample/picking
One solution is to hit test against the sprite's original, unrotated bounding box.
So given the 2D screen vector (x,y):
translate the 2D vector into local sprite space: (x,y) - (spritex,spritey)
apply inverse sprite rotation
perform hit testing against bounding box
The hit test can of course be made more accurate by taking into account the sprite shape.
I think it may be as simple as using the Contains method on Rectangle, the rectangle being the bounding box of your sprite. I've implemented drag-and-drop this way in XNA; I believe Contains tests based on x and y being screen coordinates.