Code:
// adjust_fog.c
// save as adjust_fog.c and include with 'include "adjust_fog.c";'
// controll by arrow-key: press the colorkey/s/e and adjust with arrowkeys

BMAP* bmp_background;
BMAP*	bmp_sliderbkg;
BMAP*	bmp_slider[4];
FONT* fnt = "Arial#12b";

PANEL* pan_adjust_fog = {
	
	pos_x=10;
	pos_y=10;
	
	red=5; green=0; blue=0;	
	digits (5, 10, "blue(b): %3.0f", fnt, 1, d3d_fogcolor1.blue);
	digits (5, 46, "green(g): %3.0f", fnt, 1, d3d_fogcolor1.green);
	digits (5, 80, "red(r): %3.0f", fnt, 1, d3d_fogcolor1.red);
	digits (5, 115 "start(s): %3.0f", fnt, 1, camera.fog_start);
	digits (5, 150, "end(e): %3.0f", fnt, 1, camera.fog_end);
	
	flags=VISIBLE;
}

function fogcolor_startup(){
	
	// slider bkg
	bmp_sliderbkg=bmap_createblack(100,4,16);
	
	// create slider
	bmp_slider[0]=bmap_createblack(16,32,16);
	bmp_slider[1]=bmap_createblack(16,32,16);
	bmp_slider[2]=bmap_createblack(16,32,16);
	bmp_slider[3]=bmap_createblack(16,32,16);
	bmap_fill(bmp_slider[0], vector(200,10,10), 100);
	bmap_fill(bmp_slider[1], vector(10,200,10), 100);
	bmap_fill(bmp_slider[2], vector(10,10,200), 100);
	bmap_fill(bmp_slider[3], vector(200,200,200), 100);
	
	// create and set bkg
	bmp_background=bmap_createblack(200,180,16); 
	bmap_fill(bmp_background, vector(255,255,255), 100);
	pan_adjust_fog.bmap=bmp_background;
	
	// ste the slider
	pan_setslider(pan_adjust_fog, 0, 80,  5, bmp_sliderbkg, bmp_slider[0], 0, 255, d3d_fogcolor1.blue); 
	pan_setslider(pan_adjust_fog, 0, 80, 40, bmp_sliderbkg, bmp_slider[1], 0, 255, d3d_fogcolor1.green); 
	pan_setslider(pan_adjust_fog, 0, 80, 75, bmp_sliderbkg, bmp_slider[2], 0, 255, d3d_fogcolor1.red); 
	pan_setslider(pan_adjust_fog, 0, 80, 110, bmp_sliderbkg, bmp_slider[3], 0, 30000, camera.fog_start); 
	pan_setslider(pan_adjust_fog, 0, 80, 145, bmp_sliderbkg, bmp_slider[3], 0, 30000, camera.fog_end); 
	
	fog_color=1;
	
	// controll by arrow-key (press the colorkey and adjust with arrowkeys)
	while(1){		
		if(key_b){d3d_fogcolor1.blue=clamp(d3d_fogcolor1.blue+key_force.x, 0, 255);}
		if(key_g){d3d_fogcolor1.green=clamp(d3d_fogcolor1.green+key_force.x, 0, 255);}
		if(key_r){d3d_fogcolor1.red=clamp(d3d_fogcolor1.red+key_force.x, 0, 255);}		
		if(key_s){camera.fog_start=clamp(camera.fog_start+key_force.x*100, 0, 30000);}		
		if(key_e){camera.fog_end=clamp(camera.fog_end+key_force.x*100, 0, 30000);}		
		wait(1);
	}
	
}