Sweeping surface of frequency and amplitudes

sine.c

/*
 * sine.c
 * 
 * Copyright 2022 xsbee <xyesbee@proton.me>
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02110-1301, USA.
 * 
 * 
 */

#include <math.h>

#include "SDL.h"

#define M_TAU (2 * M_PI)

struct context {
	/// Frequency of the wave.
	float f;
	
	/// Amplitude of the wave.
	float A;
	
	/// Phase offset it left at last callback.
	float p;
	
	/// Phase step
	float s;
};

void sine(void *userdata, Uint8* stream, int len) {
	struct context *c = userdata;
	
	float *x = (float*) stream;
	int N = len / sizeof(float);
	
	float A = c->A;
	float f = c->f;
	float p = c->p;
	float s = c->s;
	
	for (int i = 0; i < N; ++i)
	{	
		x[i] = A * sinf(M_TAU * f * p);
		
		p += s;
	}
	
	c->p = fmod(p, M_TAU);
}

int main(int argc, char** argv) {
		SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO);
	
		SDL_AudioDeviceID dev = 0;
		SDL_AudioSpec want, have;
		SDL_Event evt;
		SDL_Window *win = NULL;
		
		struct context *c = malloc(sizeof(struct context));
		
		c->p = 0;
		c->A = 1.0f;
		c->f = 440.0f;
		
		SDL_memset(&want, 0, sizeof(SDL_AudioSpec));
		
		want.freq = 48000;
		want.samples = 512;
		want.format = AUDIO_F32SYS;
		want.channels = 1;
		want.callback = sine;
		want.userdata = c;
		
		dev = SDL_OpenAudioDevice(NULL, 0, &want, &have, 
								  SDL_AUDIO_ALLOW_SAMPLES_CHANGE);
								  
		if (!dev) {
			fprintf(stderr, "SDL_OpenAudioDevice(): %s\n", SDL_GetError());
			goto end;
		}
		
		c->s = 1.0f / (float)have.freq;
		
		win = SDL_CreateWindow("sine",  SDL_WINDOWPOS_UNDEFINED,
										SDL_WINDOWPOS_UNDEFINED,
										800, 600,
										SDL_WINDOW_MAXIMIZED |
										SDL_WINDOW_RESIZABLE);
										
		if (!win) {
			fprintf(stderr, "SDL_CreateWindow(): %s\n", SDL_GetError());
			goto end;
		}
								  
		SDL_PauseAudioDevice(dev, 0);
		
		float w, h;
		
		for (; SDL_WaitEvent(&evt); ) {
			switch (evt.type) {
			case SDL_QUIT:
				goto end;
				
			case SDL_WINDOWEVENT:
				if (evt.window.event == SDL_WINDOWEVENT_RESIZED) {
					w = evt.window.data1;
					h = evt.window.data2;
				}
			break;
			
			case SDL_MOUSEMOTION:
				c->f = (float)evt.motion.x / w * 2000.0f;
				c->A = 1.0f - (float)evt.motion.y / h;
			break;
			}
		}
end:	
		if (win)
			SDL_DestroyWindow(win);
			
		if (dev > 0)
			SDL_CloseAudioDevice(dev);
			
		if (c)
			free(c);
			
		SDL_Quit();
}

To compile run

gcc -Ofast -o sine sine.c `pkg-config sdl2 --cflags --libs`

// TODO make transitions more smoother with interpolation