• Create Account

# apatriarca

Member Since 03 Jul 2006
Offline Last Active Today, 01:05 AM

### #5145703Quaternions rotation code

Posted by on 09 April 2014 - 09:55 AM

When you multiply two quaternions you are composing the two transformations together. The resulting rotation is the rotation obtained by first rotating according to right-most quaternion and then according to the left-most one. In your case, your first rotation maps (0, 1, 0) to mFrontWheelNormal and you then rotate around the normal vector by the angle Source.rotation.eulerAngles.y.

### #5145085Rotate a quaternion

Posted by on 07 April 2014 - 10:44 AM

If you want to combine rotations, you have to multiply together the two quaternions. If q_1 is the first rotation and q_2 is the second rotation, then q_2*q_1 is the rotation obtained by first rotating using q_1 and then q_2. q_1*q_2 is the rotation obtained by first rotating using q_2 and then q_1. Indeed, q_2*q_1*v*(q_2*q_1)^{-1} = q_2*(q_1*v*q_1^{-1})*q_2^{-1}.

### #5142607draw 2d line with clipping

Posted by on 27 March 2014 - 09:56 AM

There is no need to execute the loop to obtain the correct values of x, y and error. The error is simply the vertical distance from the line to the current pixel. If (x_0, y_0) the better approximation of the first pixel to draw on the screen and y = m*x + q is the line equation, then error = m*x_0 + q - y_0. You should then be able to draw the following pixels without problems.

### #5142534Help with Plasticity formula.

Posted by on 27 March 2014 - 05:30 AM

That arrow is usually used when describing algorithms and represents an assignment, an update of the variable the arrow points to. ||Sp - I||2 is the spectral norm of the matrix Sp - I. The spectral norm of a matrix A is the square root of the maximum eigenvalue of AHA where AH is the conjugate transpose of A (the transpose if the matrix is real).

### #5140930Quaternions: convert between Left-Right handed without using Euler

Posted by on 21 March 2014 - 06:09 AM

Let M be the (3x3) transformation matrix between the Blender coordinate system and the Unity one. Then the axis is simply transformed using M and the angle should change sign (since M does not preserve the orientation). You thus have to negate the imaginary part and then apply M to it.

EDIT:

The transformation between Blender and Unity coordinate systems is, if I remember correctly, (x, y, z) -> (y, z, -x). If I thus have a quaternion q0 + q1*i + q2*j + q3*k, the corresponding quaternion should be q0 - q2*i - q3*j +q1*k.

### #5140688Inverse Proportion and Zero

Posted by on 20 March 2014 - 09:57 AM

I'm not sure I understood your post. Anyway, what about (10 - x)*25.5 ? It is equal to 255 when x is zero and equal to 0 when x is 10.

### #5134720This is what atan2() does if given two Vector2D points on 2D plane?

Posted by on 26 February 2014 - 05:07 AM

There is no need to convert these vectors to angles to compute a rotation matrix. All you need to compute a rotation matrix in 2D are the cosine and sine of the angle and you already have them encoded in the direction of the difference vector. You indeed simply have to normalize the difference vector:

(cos(angle), sin(angle) ) = normalize(P2 - P1).

If you think you have to compute the angle to compare them between different fingers positions, then it is not true again. If P3 and P4 are different positions of your fingers, then you can compute the cosine and sine of the rotation angle between the two vectors by simply using a complex division. If do not know complex numbers I suggest to learn about them, but you can implement the division using the following formula:

(a, b) / (c, d) = ( a*c + b*d, b*c - a*d ) / (c*c + d*d).

### #5125823.obj file loader

Posted by on 23 January 2014 - 03:30 AM

Is there any reason you are using (*model).GetIndices() instead of model->GetIndices() ?

### #5125637Barycentric coordinates of circumcenter of tetrahedron

Posted by on 22 January 2014 - 08:10 AM

The steps in the derivation are very similar to the steps in the triangle case and you should get:

Dot(B-A,B-A)*s + Dot(B-A,C-A)*t + Dot(B-A,D-A)*u = (1/2)*Dot(B-A,B-A)
Dot(C-A,B-A)*s + Dot(C-A,C-A)*t + Dot(C-A,D-A)*u = (1/2)*Dot(C-A,C-A)

Dot(D-A,B-A)*s + Dot(D-A,C-A)*t + Dot(D-A,D-A)*u = (1/2)*Dot(D-A,D-A)

which you can then solve using Cramer's rule (or something else).

### #5125616Mathematics for 3D programming - Exercises

Posted by on 22 January 2014 - 05:01 AM

Making a simple 3D game/tech demo or a ray tracer or .. is IMHO probably one of the best way to exercise those math skills.

### #5123310Need a design advice on a Mesh Class

Posted by on 13 January 2014 - 10:53 AM

If Context::CreateBuffer calls Mesh::CreateBuffer you have an infinite loop. This is in my opinion the main reason to avoid doing that.

### #5123269shadows in 2d

Posted by on 13 January 2014 - 07:18 AM

I guess it depends on the type of game you are working on (i.e. where is the camera and the relative positions of lights and objects) but it can be done. For example, this article on gamedev explains a technique to implement soft shadows in 2D.

### #5117517Genetic algorithm in a game

Posted by on 17 December 2013 - 02:44 AM

You may find this paper interesting. The paper describes an experiment in which player weapons were procedurally generated at the beginning of each match. The players were able to choose between their current weapons and new procedurally generated one and their choices and performance were used to evolve the weapon generation algorithm.

### #5115643OpenGl as a blitter

Posted by on 09 December 2013 - 07:43 AM

The modern way of drawing stuffs using the GPU is to simply draw a set of textured quads. There is no reason to flush after each quad (it would be extremely slow) and it is usually easier to simply draw everything each frame. There are several ways to draw a quad in OpenGL: you can draw two triangles, you can use the GL_QUADS constant (in legacy versions of OpenGL), you can use point sprites, you can use a geometry shader, you can use instancing, etc. In a simple 2D game, the method used is probably not so important.

P.S. If you really want to learn about OpenGL, I suggest to start using the modern APIs. The programmable pipeline is now common in the mobile and Web world too.

### #5114300Using one instance of Behaviour Tree for many agents?

Posted by on 04 December 2013 - 07:07 AM

I think there was a video tutorial on AiGameDev.com discussing these topics. Probably this video.

PARTNERS