Good eve all!
I'm making simple model editor on WPF for creating cube-head freaks with pixelate skins and want add billboarding to it.
So, what I do
Vector3D unitZ = new Vector3D(0, 0, 1);
Vector3D direction = -this.camera.LookDirection;
double yaw = Vector3D.AngleBetween(unitZ, new Vector3D(0, 0, direction.Z));
and the apply rotation to plane.
It works, but only on half, couse AngleBetween function allways returns positive values.
So when I rotate parent shape to -45 degrees AngleBetween returns 45 and it annihilate parent rotation. But when I rotate parent on 45 degrees AngleBetween again returns 45 and in result I got 90 degrees rotation.
Any solutions?
And one more thing: please, do not offer any frameworks or toolkits! Thanks.
Well, that's how AngleBetween method works for 3D vectors in WPF. It returns value in the range of [0..180] degrees.
As far as your problem goes, I am not 100% I understand you. The angle between [0, 0, 1] and [0, 0, arbitrary number here] can only give you three different values: :
impossible to calculate
180
0
-180 if signed is possible.
As I don't really see how you can ever get 45.
Either way, it's possible that you can use Vector.AngleBetween which should preserve the sign. That will work if your rotation is only on one axis, eg one of the components stay the same.
If that does not suit your needs, you should just write what you need: Signed angle between two 3D vectors with same origin within the same plane
Related
Selecting a random color on a computer is a touch harder than I thought it would be.
The naive way of uniform random sampling of 0..255 for R,G,B will tend to draw lots of similar greens. It would make sense to sample from a perceptually uniform space like CIELUV.
A simple way to do this is to sample L,u,v on a regular mesh and ensure the color solid is contained in the bounds (I've seen different bounds for this). If the sample falls outside embedded RGB solid (tested by mapping it XYZ then RGB), reject it and sample again. You can settle for a kludgy-but-guaranteed-to-terminate "bailout" selection (like the naive procedure) if you reject more then some arbitrary threshold number of times.
Testing if the sample lies within RGB needs to be sure to test for the special case of black (some implementations end up being silent on the divide by zero), I believe. If L=0 and either u!=0 or v!=0, then the sample needs to be rejected or else you would end up oversampling the L=0 plane in Luv space.
Does this procedure have an obvious flaw? It seems to work but I did notice that I was rolling black more often than I thought made sense until I thought about what was happening in that case. Can anyone point me to the right bounds on the CIELUV grid to ensure that I am enclosing the RGB solid?
A useful reference for those who don't know it:
https://www.easyrgb.com/en/math.php
The key problem with this is that you need bounds to reject samples that fall outside of RGB. I was able to find it worked out here (nice demo on page, API provides convenient functions):
https://www.hsluv.org/
A few things I noticed with uniform sampling of CIELUV in RGB:
most colors are green and purple (this is true independent of RGB bounds)
you have a hard time sampling what we think of as yellow (very small volume of high lightness, high chroma space)
I implemented various strategies that focus on sampling hues (which is really what we want when we think of "sampling colors") by weighting according to the maximum chromas at that lightness. This makes colors like chromatic light yellows easier to catch and avoids oversampling greens and purples. You can see these methods in actions here (select "randomize colors"):
https://www.mysticsymbolic.art/
Source for color randomizers here:
https://github.com/mittimithai/mystic-symbolic/blob/chromacorners/lib/random-colors.ts
Okay, while you don't show the code you are using to generate the random numbers and then apply them to the CIELUV color space, I'm going to guess that you are creating a random number 0.0-100.0 from a random number generator, and then just assigning it to L*.
That will most likely give you a lot of black or very dark results.
Let Me Explain
L* of L * u * v* is not linear as to light. Y of CIEXYZ is linear as to light. L* is perceptual lightness, so an exponential curve is applied to Y to make it linear to perception but then non-linear as to light.
TRY THIS
To get L* with a random value 0—100:
Generate a random number between 0.0 and 1.0
Then apply an exponent of 0.42
Then multiply by 100 to get L*
Lstar = Math.pow(Math.random(), 0.42) * 100;
This takes your random number that represents light, and applies a powercurve that emulates human lightness perception.
UV Color
As for the u and v values, you can probably just leave them as linear random numbers. Constrain u to about -84 and +176, and v to about -132.5 and +107.5
Urnd = (Math.random() - 0.5521) * 240;
Vrnd = (Math.random() - 0.3231) * 260;
Polar Color
It might be interesting converting uv to LChLUV or LshLUV
For hue, it's probably as simple as H = Math.random() * 360
For chroma contrained 0—178: C = Math.random() * 178
The next question is, should you find chroma? Or saturation? CIELUV can provide either Hue or Sat — but for directly generating random colors, it seems that chroma is a bit better.
And of course these simple examples are not preventing over-runs, so they color values to be tested to see if they are legal sRGB or not. There's a few things that can be done to constrain the generated values to legal colors, but the object here was to get you to a better distribution without excess black/dark results.
Please let me know of any questions.
What happens if i a make a rotation on a scenekit node object this way:
node.rotation = SCNVector4Make(1, 0, 0, M_PI_2)
Does it adds PI/2 to existing rotation or does it set object angle to PI/2?
In other words what happens if i call twice this line:
node.rotation = SCNVector4Make(1, 0, 0, M_PI_2)
Does it rotate to PI/2 or PI ?
I have the same question for node.eulerAngles property
Thanks
none of the SCNNode properties regarding transforms is "cumulative", just like the transform of a CALayer for instance. To combine transforms you'll want to use utils such as SCNMatrix4Rotate.
While I'll never argue with what is in SceneKit with mnuages (I think he works on it at Apple), I will contend that he's taken your question too literally.
If you are looking for cumulative rotation, it is available in SceneKit, if you know how much rotation you want. You can use the two rotateBy SCNActions.
They are :
rotateBy(x:y:z:duration:)
and:
rotate(by:around:duration:)
Both of these, applied repeatedly, will cumulatively add to the rotation of your object.
I am looking for suggestions as how to create plots similar to GitHub punch cards with JFreeChart. E.g.
I guess it's some variant of a heat map, or two dimensional histogram.
Ok, so I found XYBubbleRenderer which looks like a good starting point.
create a MatrixSeries with rows = 7, columns = 24
fill in the frequencies accordingly. I found it useful to normalise the values first to 0...1, then take the square root (smaller values have a bit better visible circles), then multiply by 0.5 (otherwise the circles are too large)
create a MatrixSeriesCollection from that
use ChartFactory.createBubbleChart
the circle outline can only be removed via plot.getRenderer.setSeriesOutlinePaint(0, new Color(0, 0, 0, 0))
ensure integer tick units on both axis
x-axis range -0.5 to 23.5, y-axis range -0.5 to 6.5 (or 0.5 to 7.5 if you use Calendar.DAY_OF_WEEK)
custom NumberTickUnit for the y-axis to use day labels instead of numbers
The result:
In addition to XYBubbleRenderer, suggested here, also consider a suitable implementation of TableCellRenderer and Icon, illustrated here.
I am creating a 3D graphics engine and one of the requirements is ropes that behave like in Valve's source engine.
So in the source engine, a section of rope is a quad that rotates along it's direction axis to face the camera, so if the section of rope is in the +Z direction, it will rotate along the Z axis so it's face is facing the camera's centre position.
At the moment, I have the sections of ropes defined, so I can have a nice curved rope, but now I'm trying to construct the matrix that will rotate it along it's direction vector.
I already have a matrix for rendering billboard sprites based on this billboarding technique:
Constructing a Billboard Matrix
And at the moment I've been trying to retool it so that Right, Up, Forward vector match the rope segment's direction vector.
My rope is made up of multiple sections, each section is a rectangle made up of two triangles, as I said above, I can get the position and sections perfect, it's the rotating to face the camera that's causing me a lot of problems.
This is in OpenGL ES2 and written in C.
I have studied Doom 3's beam rendering code in Model_beam.cpp, the method used there is to calculate the offset based on normals rather than using matrices, so I have created a similar technique in my C code and it sort of works, at least it, works as much as I need it to right now.
So for those who are also trying to figure this one out, use the cross-product of the mid-point of the rope against the camera position, normalise that and then multiply it to how wide you want the rope to be, then when constructing the vertices, offset each vertex in either + or - direction of the resulting vector.
Further help would be great though as this is not perfect!
Thank you
Check out this related stackoverflow post on billboards in OpenGL It cites a lighthouse3d tutorial that is a pretty good read. Here are the salient points of the technique:
void billboardCylindricalBegin(
float camX, float camY, float camZ,
float objPosX, float objPosY, float objPosZ) {
float lookAt[3],objToCamProj[3],upAux[3];
float modelview[16],angleCosine;
glPushMatrix();
// objToCamProj is the vector in world coordinates from the
// local origin to the camera projected in the XZ plane
objToCamProj[0] = camX - objPosX ;
objToCamProj[1] = 0;
objToCamProj[2] = camZ - objPosZ ;
// This is the original lookAt vector for the object
// in world coordinates
lookAt[0] = 0;
lookAt[1] = 0;
lookAt[2] = 1;
// normalize both vectors to get the cosine directly afterwards
mathsNormalize(objToCamProj);
// easy fix to determine wether the angle is negative or positive
// for positive angles upAux will be a vector pointing in the
// positive y direction, otherwise upAux will point downwards
// effectively reversing the rotation.
mathsCrossProduct(upAux,lookAt,objToCamProj);
// compute the angle
angleCosine = mathsInnerProduct(lookAt,objToCamProj);
// perform the rotation. The if statement is used for stability reasons
// if the lookAt and objToCamProj vectors are too close together then
// |angleCosine| could be bigger than 1 due to lack of precision
if ((angleCosine < 0.99990) && (angleCosine > -0.9999))
glRotatef(acos(angleCosine)*180/3.14,upAux[0], upAux[1], upAux[2]);
}
I have a "FlattenedPathGeometry" and I want to be able to get a specific point.X from the path based on a specific Point.Y
Basically I just need the X value at any given Y.
Thanks in advance for any help.
GetFlattenedPathGeometry gives you back a polygonal so basically you have to consider loop all the points and calculating the minimum distance to your point.
If you can make any assumption on the Geometry shape or your point, you can speed up the search.
For example if the path is very long, you can speed up by intersecting the shape with a circle/square centered in your point. This limit the number of points of the shape to test but be careful that the intersection method is very expensive. You'll have to measure the performances with a stopwatch to understand what's better in your case.