What is the best way to plot a spectrogram with openGL

Question

I have written a code to calculate the spectrogram of a sine & cos signals, applied the Hann Window, calculated FFT, Calculated log magnitude of frequency coefficients.

I tested that it is all working by writing a simple function in openGL to plot a magnitude-frequency spectrum and I got the following results:

As you can see, there are 2 bars which indicates the sine * cos waves.

I have all the information I need to plot a spectrogram (frequencies,magnitude,time) Now my question is how can I draw that? my first thought was to draw dots, so I'll use the time array for the interval time I need to draw the dots on the X axie, frequencies array to where to draw them on the Y axis, and the magnitude would be the color of the dot.

Maybe that's an inefficient idea because I saw that drawing dots is really inefficient in openGL so I don't know what's a better idea, I couldn't find any "simple" examples of openGL spectrogram online.

Make an array of colors, fill it once, then give it to GL as a texture. — HolyBlackCat, May 22 '21 at 11:54
oh so instead of doing what I said which is drawing every dot individually I just put it in that array and give GL that as a texture? — yarin Cohen, May 22 '21 at 11:58
why not try using framebuffer for it let the given equation to plot be y=f(x) now just check if it satisfies. and if it does then out a colored pixel else color the fragment black. and after that apply maybe a spread shader to get thicker line.!? — PrashanththKumar0, May 22 '21 at 12:01
I'm using glew-1.11.0 because I couldn't find another version which include the "include" and "lib" folders @AdrianMaire — yarin Cohen, May 22 '21 at 12:45
you should have access to OpenGL 4.5 with glew-1.11. So you are **not** using glVertex and such right? — Adrian Maire, May 22 '21 at 13:37
why not pass the FFT result as texture and compute the dots (you wanted in first place) inside Fragment shader? They are ideal for this. — Spektre, May 23 '21 at 06:56

score 0 · Answer 1 · answered May 23 '21 at 11:48

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@HolyBlackCat comment is the answer

"Make an array of colors, fill it once, then give it to GL as a texture"

answered May 23 '21 at 11:48

yarin Cohen

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What is the best way to plot a spectrogram with openGL

1 Answers1