# Tag Info

69

No this isn't an engine bug or an artifact of a particular rotation representation (those can happen too, but this effect applies to every system that represents rotations, quaternions included). You've discovered a real fact about how rotation works in three-dimensional space, and it departs from our intuition about other transformations like translation: ...

37

X = x*cos(θ) - y*sin(θ) Y = x*sin(θ) + y*cos(θ) This will give you the location of a point rotated θ degrees around the origin. Since the corners of the square are rotated around the center of the square and not the origin, a couple of steps need to be added to be able to use this formula. First you need to set the point relative to the origin. Then you ...

35

Fake it Look at the video you linked, watch it in slow motion... eh, what is that? The camera jumps at the end, and the knife is already in the helmet of the target. Just fake it. Once the distance from the knife to the target is small, jump cut to the knife magically in the target. Edit: you can check if it will hit a target using the convoluted ...

32

The answer is actually pretty easy if you do the math. You have a fixed distance of Y and a variable distance of X (See Picture 1). You need to find out the angle between Z and X and turn your turret that much more. Step 1 - Get distance between the turret line (V) and the gun line (W) which is Y (this is constant but doesn't hurt to calculate). Get ...

27

Have you considered that it looks very odd for a person to standing perpendicular to a slope? You need to be upright to stay in balance. Some alternatives: Treat his feet as a separate object and rotate them to be parallel to the slope. (A raycast will find the angle's normal, as dnk described. The angle for the feet is that + 90°.) Fake it, by moving ...

24

Multiplication At least in terms of Unity's implementation of Quaternions, the multiplication order described in the question is not correct. This is important because 3D rotation is not commutative. So, if I want to rotate an object by rotationChange starting from its currentOrientation I'd write it like this: Quaternion newOrientation = rotationChange * ...

17

Have a look at RotSprite. RotSprite is a scaling and rotation algorithm for sprites developed by Xenowhirl. It produces far fewer artifacts than nearest-neighbor rotation algorithms, and like EPX, it does not introduce new colors into the image (unlike most interpolation systems). The algorithm first scales the image to 8 times its original size with a ...

15

The problem with rotations, is that, most people think of it in terms of Euler angles, since they are easy to understand. Yet most people forget the point that Euler angles are three sequential angles. Meaning that rotation around the first axis, will make next rotation be relative to the first original rotation, hence you cannot independently rotate a ...

15

Where's the dot product used? In Unity, one of the most common users of the dot product is whenever you check if two quaternions are equal via == or !=. Unity computes the dot product to check similarity rather than directly comparing the internal x,y,z,w values. It's worth keeping this one in mind as it makes the call more expensive than you might expect it ...

15

Automatic rotation of pixel art by other angles than 90° usually goes wrong. If you want to maintain the pixel-art aesthetics you usually won't get around redrawing your art in each angle. If you use a faux-retro look where your sprites are actually in a far higher resolution than they look, you can sometimes get away with upscaling them by an integer ...

14

If you know ahead of time where the knife will land - like in those kill cam footage, which is most definitely produced after-the-fact - just calculate the right rotation speed based on flight distance and number of rotations desired. Throwing knives leave the thrower hilt-first, so it needs to rotate N+0.5 full rotations1, where N is usually at least 1 but ...

14

Calculate the straight line distance to target. Each Frame set the angle of the knife to be 2PI*(remainingStraightLineDistance)/(originalStraightLineDistance)*DesiredNumRotations. The spin ratio will vary slightly if you don't move the knife in a straight line but no-one will ever notice. If you don't pre-determine the target (i.e. you're just throwing and ...

12

You should probably use glm::angleAxis() (documentation here): glm::quat rot = glm::angleAxis(glm::radians(90.f), glm::vec3(0.f, 1.f, 0.f));

11

As long as you're doing only uniform scaling, this is easy; you can simply extract each row (or column; it doesn't matter), of the 3x3 matrix. The scale factor will be the length of the row vector. If you normalize each row vector and construct a new matrix from the normalized rows, that will be the rotation part. (If you have a 4x4 matrix, you just do ...

10

It’s important to note that changing the co-ordinate system with rotate and translate do not affect anything that’s currently drawn into the canvas. It only affects subsequent drawing actions. var TO_RADIANS = Math.PI/180; function drawRotatedImage(image, x, y, angle) { // save the current co-ordinate system // before we screw with it ...

9

Make the moon a child of the planet object, and the planet a child of the star. Now, if the moon wasn't orbiting, it will stay with the planet in its orbit. You can easily rotate an arbitrary point around another arbitrary point with the following: public static Vector3 RotatePointAroundPivot(Vector3 point, Vector3 pivot, Quaternion angle) { return ...

9

The Problem: Your eyes default rotation makes them look to the negative X axis. However, Transform.LookAt() rotates the transform, so that the Transform.forward looks at the target. The Transform.forward always looks to the positive Z axis. (All directions in local space). Solution 1: Rotate the texture or mesh, so that the eye's default look direction is ...

8

Conceptually, you can do that by animating the rotation of the cube (or as in Bloxorz, a cuboid) 90 degrees around one of its edges. You don't need move() at all! Side-on view of one rotation: Here's a seriously good JMonkeyEngine tutorial showing you how to rotate Boxes around pivot Nodes. It explains everything step-by-step. These are the important lines:...

7

Roy T. suggested to fix this changing the texture filtering settings, On LibGDX this can be found on Texture.setFilter or changing the Texture Params if you are using the AssetLoader. Set the filter params to TextureFilter.Linear and the problem should be fixed. For more on the matter, take a look at http://www.learnopengles.com/android-lesson-six-an-...

6

Instead of drawing the rotated image out to another image where you then draw that image out to Graphics to be displayed... why don't you draw directly to that Graphics object? This way it saves ALOT more time and doesn't waste memory. Graphics2D g2d = ... AffineTransform backup = g2d.getTransform(); AffineTransform trans = new AffineTransform(); trans....

6

Simple Solution If you want the body to instantly rotate just call Body::setTransform and pass the current position and the desired angle, don't bother applying torques or anything. The function call could be something like this: body.setTransform(body.getPosition(),myDesiredAngle); Physics Solution If you want the player body to interact with bodies ...

6

If you wish for an object to orbit around a specified point in two dimensional space, you want to use some trigonometric functions. Here is an example method to calculate an objects position in an orbit: class OrbitUtilities { /* currentOrbitDegrees: the degrees around the orbit that the satellite is(can greater that 360(361 would be equivalent to 1)) ...

6

You need to put a cap on how big rotationAngle is allowed to be. Right now, as the difference between the mouse and the "player" grows larger, your "player" rotates more quickly to catch up. But in order to put a "minimum turn radius" on your object, you need to restrict how quickly it can change direction. Try this: float rotationAngle = Vector3.Cross(...

6

A quaternion can be thought of as an angle-axis representation: quaternion.xyz = sin(angle/2) * axis.xyz quaternion.w = cos(angle/2) So, converting them between two coordinate systems can be broken down into two steps: Map the axis into the new coordinate system. If changing between left & right hand coordinates (eg. if there's an odd number of axis ...

5

Think about what you need to do, open the door over time. It's not going to happen all in one call in the Start function. You'll need to add a little more rotation each frame to rotate the object smoothly. Something like the following will rotate the object from 0 to 90 degrees over time: void Update () { SwingOpen(); } void SwingOpen() { ...

5

Each orientation in 3D space can be represented by 2 distinct unit quaternions, q and -q (component-wise negated q). For instance the orientation represented by the 3x3 identity matrix I can be represented by 2 quaternions: q: { 0, 0, 0}, 1 -q: {-0, -0, -0}, -1 Both represent the same orientation in 3D space, their dot product is exactly -1, each of ...

5

This is a late response, but I figured this question illustrates a common problem that many people are likely to run into and that deserves an answer. Quaternion rotation uses half the angle you want to rotate by. Since you (in this example case) are rotating by 90 degrees, the quaternion needs to calculate the sine and cosine of 45 degrees, both of which ...

5

The method camera.rotate() (and all other transformation methods on camera) act on the current state of the camera. So if it's rotated 30 degrees, it will add more 30 degrees to the rotation. If you want to keep at 30 degrees (but still applying the transform every step), you have to make it look back at whatever it was looking before. Assuming you're using ...

5

Start by adding a variable for the angle that the car is moving at. float angle = Math.Pi / 2; Then add a variable for the current speed. float speed = 0.0; Now create three constants: public static final float acceleration = 0.1; public static final float maxSpeed = 5.0; public static final float rotationRate = Math.Pi / 50; For starters, get your ...

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