# OpenGL Random, but intelligent, colour selection

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Hi, Im writing an OpenGl application that draws database data on top of a textured map. Currently im working on grouping the data by different fields and selecting a colour for the different groups. At the moment my colour choosing algorithm simply chooses a random red, green and blue value for each field but this often chooses poor colours and there are also duplicates (obviously). I just wondered if there was some sort of algorithm that could generate a set number of colours that werent too similar? Regards, Matt

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I would create by hand a color palette and get a random color from this palette

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Thanks,

I would do this but sometimes upto 100 colours may be required so an algorithm would be ideal!!

Any other ideas?

Matt

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You should look for a function that will look something like this:
F((R1, G1, B1), (R2, G2, B2))
The larger the value of the function, the better a human eye can differ between the two colors.
I am not sure if it is easy to find this sort of function, but you probabbly need to look into image processing to find something like this.
After having this function F, you should find an algorithem that gives you n colors so that the minimum of F between all these n colors, is as large as possible.
Hope that helps.

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Quote:
 Original post by SoapsurgeonThanks, I would do this but sometimes upto 100 colours may be required so an algorithm would be ideal!!Any other ideas?Matt

You could make an array with N slots and generate colors into that with a for loop. For distinct colors, I would suggest using 8 red shades, 8 green shades and 8 blue shades. (with the lowest being 0 and the highest being 255, the other 6 between these two) With this you can make 8*8*8=512 distinct colors, put them into a table, and select a color for each group. Since there are only 8 shades of each color component is used, it's much easier to distinguish between them. If you only need 64 colors, you can use 4 shades per color channel (4*4*4=64).

Viktor

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consider your colors to be vectors in color-space: [0,1]X[0,1]X[0,1]

Now, I don't know how bright you want your colors to be, but when I do random color generation, I generate vectors on the unit sphere constrained to color space. Then, to compare how 'close' two colors are, I do a dot product, if that's below some threshold (say 0.8) then I assume they are far enough apart that I can use them both safely.

I've written a geological imaging tool, and from working with the users alot, I found that they suffer from information overload really really fast. So generally, they didn't want to see more than three types of samples at a time, and they wanted a few simple color palettes to view them with.

Now, I don't know what your application is, but I suspect you'll want to be careful about how much data you display. Also consider coloring related fields with similar colors.

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Hi,

thanks for the replies, I'll try and knock something up.

FYI my project is to do with bird watching! the users can query what birds have been seen where so if they desired they could have all birds seen in a 10km square, say. This could have up to 350 different birds which, if they choose group by bird, would need 350 different colours. This is an extreme example and for the majority of the time i guess i will only need 3,4 or 5 colours but i just wanted an algorithm to handle every scenario.

Matt

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I've used an algorithm like the one below for this a similar task, please note that I don't remeber the exact algorithm, just that I gave all components a medium range intensity [64, 128], then randomly gave one or two components extra strength:

unsigned char rgb[3];// Get random valuesrgb[0] = rand() & 0x3f;rgb[1] = rand() & 0x3f;rgb[2] = rand() & 0x3f;// Make sure they are not so darkrgb[0] += 0x40;rgb[1] += 0x40;rgb[2] += 0x40;// Make one of the primaries exta strongint i = ((rand() & 0xfff) * 3) >> 12; // [0, 2]rgb += 0x80;// Maybe make one of other primaries stand outif ((rand() & 0xfff) < 0x7fff){  i += ((rand() >> 11) & 1);  i %= 3;  rgb += 0x80;}

Disclaimer: I haven't compiled the code above...

Edit: I you want darker colors shift down:
rgb[x] = rbg[x] >> 1;
Brighter:
rgb[x] = (rbg[x] >> 1) + 0x80;

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You'll probably find it much easier to come up with an algorithm if you work in HSL colour space (hue, saturation, lightness) rather than RGB. You can then convert to RGB as a last step before drawing.

http://en.wikipedia.org/wiki/HLS_color_space

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I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
Brain.cpp
Error.cpp
IndexBuffer.cpp
Input.cpp
Renderer.cpp
Scene.cpp
Sprite.cpp
Texture.cpp
VertexArray.cpp
VertexBuffer.cpp
VertexBufferLayout.cpp
Window.cpp
Brain.h
Error.h
IndexBuffer.h
Input.h
Renderer.h
Scene.h
SpaceShooterEngine.h
Sprite.h
Texture.h
VertexArray.h
VertexBuffer.h
VertexBufferLayout.h
Window.h

• Hello fellow programmers,
For a couple of days now i've decided to build my own planet renderer just to see how floating point precision issues
can be tackled. As you probably imagine, i've quickly faced FPP issues when trying to render absurdly large planets.

I have used the classical quadtree LOD approach;
I've generated my grids with 33 vertices, (x: -1 to 1, y: -1 to 1, z = 0).
Each grid is managed by a TerrainNode class that, depending on the side it represents (top, bottom, left right, front, back),
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normalize all the vertices on my vertex shader i can get a perfect sphere.
T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as r_Grid'.
// spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The r_ModelViewProjection' matrix is generated on the CPU in this manner.
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Each frame i'm rendering each node by sending the generated matrices this way.
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Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
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I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
getting rid of those rounding errors.

My question is how can i achieve this relative to camera rendering in my scenario here?
I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
I only use double on the CPU side where i also do most of the matrix multiplications.
As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).