Simple spinner with variable speed and size

oled_spinner.c

//Call at least every 10ms 
void oled_spinner() {
    int x = 64, y = 35, r = 15;
    
    static uint32_t millis = board_millis();
    static float angle = 0;

    if (board_millis() - millis < 10) return;
    millis += 10;

    oledFill(&oled, 0x00, false);
    
    angle += (angle - 3.1415) * (angle - 3.1415) / 130 + 0.08;
    float size = (angle - 3.1415) * (angle - 3.1415) / 20 + 0.55;

    float spinner_start_angle = angle;
    float spinner_end_angle   = spinner_start_angle + size;

    for (float spinner_angle = spinner_start_angle; spinner_angle < spinner_end_angle; spinner_angle += 0.05) {
        for(float thickness=0; thickness < 2.5; thickness += 0.5) {
            oledSetPixel(&oled, x + cos(spinner_angle) * (r-thickness), y + sin(spinner_angle) * (r-thickness), 0x01, false);
        }
    }
    if(angle > 6.28) angle = 0;

	oledDumpBuffer(&oled, oled_buffer);
}