A simple graphics library in C with BMP and WMF export

/*

	Simple motion with a = dv/dt = -x
	
	10  REM DY2
	15  REM X-T GRAPH OF DY1
	20  INPUT "SCALE OF T-AXIS ="; K
	30  INPUT "SCALE OF X-AXIS ="; L
	40  HGR : HCOLOR=3
	50  HPLOT 0, 40 TO 0, 140
	60  HPLOT 0, 90 TO 279, 90
	70  X0 = 1:V0 = 0:DT = 0.1
	80  X = X0:V = V0
	90  A = -X
	100 V = V + A * (DT/2)
	110 X = X + V * DT
	120 T = T + DT
	130 T1 = T * K:X1 = X * L
	140 IF T1 > 270 THEN END
	150 HPLOT T1, -X1 + 90
	160 A = -X
	170 V = V + A * DT
	180 GOTO 110
	
	]RUN
	SCALE OF T-AXIS =5
	SCALE OF X-AXIS =40
*/

#include <stdio.h>
#include "libtg.h"

//#define BMP
#define SYMBOL
#define SYMBOL_SKIP
//#define LINE

#define SYMBOL_CIRCLE		0
//#define SYMBOL_DELTA		1
//#define SYMBOL_GRADIENT		2
//#define SYMBOL_RTRIANGLE	3
//#define SYMBOL_LTRIANGLE	4
//#define SYMBOL_DIAMOND		5
//#define SYMBOL_SQUARE		6

int main(void)
{
	float x, v, a, x0=1, v0=0, t=0, dt=0.1, k=5, l=40,x1=0,t1=0;
	float fwid=0, fhgt=5, fratio=0;
	int xwid=279, xhgt=180, skip=5, iskip=0, findex=0;
	TG_Symbol sym_index=TG_SYM_CIRCLE;
	TG_Symbol symbols[] = { TG_SYM_CIRCLE, TG_SYM_DELTA, TG_SYM_GRADIENT, TG_SYM_RTRIANGLE, TG_SYM_LTRIANGLE, TG_SYM_DIAMOND, TG_SYM_SQUARE };
	TG_Color pixel_color = TG_GetColor(TG_BLACK);
	TG_PlotZone_Ptr zone=NULL;
	TG_Workspace_Ptr workspace = TG_InitTGLibrary("Letter");
	
#ifdef BMP
	#ifdef SYMBOL 
		#ifdef SYMBOL_SKIP
		char* filename[] = { 
			"simpmtn-skip-symbol-circle.bmp", 
			"simpmtn-skip-symbol-delta.bmp",
			"simpmtn-skip-symbol-gradient.bmp",
			"simpmtn-skip-symbol-rtriangle.bmp",
			"simpmtn-skip-symbol-ltriangle.bmp",
			"simpmtn-skip-symbol-diamond.bmp",
			"simpmtn-skip-symbol-square.bmp" };
		#else
		char* filename[] = { 
			"simpmtn-symbol-circle.bmp", 
			"simpmtn-symbol-delta.bmp",
			"simpmtn-symbol-gradient.bmp",
			"simpmtn-symbol-rtriangle.bmp",
			"simpmtn-symbol-ltriangle.bmp",
			"simpmtn-symbol-diamond.bmp",
			"simpmtn-symbol-square.bmp" };
		#endif
	#else
		char* filename[] = {"simpmtn.bmp"};
	#endif
#else
	#ifdef SYMBOL
		#ifdef SYMBOL_SKIP
		char* filename[] = { 
			"simpmtn-skip-symbol-circle.wmf", 
			"simpmtn-skip-symbol-delta.wmf",
			"simpmtn-skip-symbol-gradient.wmf",
			"simpmtn-skip-symbol-rtriangle.wmf",
			"simpmtn-skip-symbol-ltriangle.wmf",
			"simpmtn-skip-symbol-diamond.wmf",
			"simpmtn-skip-symbol-square.wmf" };
		#else
		char* filename[] = { 
			"simpmtn-symbol-circle.wmf", 
			"simpmtn-symbol-delta.wmf",
			"simpmtn-symbol-gradient.wmf",
			"simpmtn-symbol-rtriangle.wmf",
			"simpmtn-symbol-ltriangle.wmf",
			"simpmtn-symbol-diamond.wmf",
			"simpmtn-symbol-square.wmf" };
		#endif
	#else
		char* filename[]={ "sympmtn.wmf" };
	#endif
#endif

#ifdef SYMBOL
	#ifdef SYMBOL_CIRCLE
		sym_index = findex = 0;
	#elif defined SYMBOL_DELTA
		sym_index = findex = 1;
	#elif defined SYMBOL_GRADIENT
		sym_index = findex = 2;
	#elif defined SYMBOL_RTRIANGLE
		sym_index = findex = 3;	
	#elif defined SYMBOL_LTRIANGLE
		sym_index = findex = 4;	
	#elif defined SYMBOL_DIAMOND
		sym_index = findex = 5;	
	#elif defined SYMBOL_SQUARE
		sym_index = findex = 6;	
	#endif
#endif

	if(!workspace) return 1;
	
	fratio = (float)xwid/(float)xhgt;
	fwid = fratio*fhgt;
	zone = &workspace->zone;
	TG_SetFrame(&workspace->zone.frame, 0, 0, fwid, fhgt, 0, xwid, 0, xhgt);

#ifdef BMP
	TG_BMP_OpenExport(zone, filename[findex], xwid, xhgt, 1);
#else
	TG_WMF_OpenExport(zone, filename[findex]);
#endif

	x = x0;	
	v = v0;
	a = -x;
	v += a*dt/2;

#ifdef BMP
	TG_BMP_SetReverseWorldCoord(1);
#else	
	TG_WMF_SetReverseWorldCoord(1);
#endif

#ifdef LINE
	zone->plot.makepen(zone, TG_GetColor(TG_BLUE), 0.005);
	zone->plot.moveto(zone, t*k, 90-x*l);
#endif
	
	while(1) {
		x += v*dt;
		t += dt;
		t1 = t*k;
		x1 = x*l;
		if(t1 > 270) break;
		a = -x;
		v += a*dt;
#ifdef LINE
		zone->plot.lineto(zone, t1, -x1+90);
#else
		zone->plot.putpixel1(zone, t1, -x1+90, pixel_color);
#endif

#ifdef SYMBOL
#ifdef SYMBOL_SKIP
		if((iskip%skip)) iskip++;
		else {
#endif
			zone->plot.gsave();
			#ifdef SYMBOL_CIRCLE 
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_RED)    ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_DELTA
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_GREEN)  ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_GRADIENT
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_BLUE)   ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_RTRIANGLE
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_YELLOW) ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_LTRIANGLE
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_CYAN)   ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_DIAMOND  
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_MAGENTA),1 ,TG_GetColor(TG_BLACK),1,0.001);
			#elif defined SYMBOL_SQUARE    
				zone->plot.symbol(zone, t1, -x1+90, symbols[sym_index],.03, TG_GetColor(TG_BROWN)  ,1 ,TG_GetColor(TG_BLACK),1,0.001);
			#endif
			zone->plot.grestore();
#ifdef SYMBOL_SKIP
			iskip=1;
		}
#endif
#endif
	}

#ifdef BMP
    TG_BMP_CloseExport();	
#else
    TG_WMF_CloseExport();
#endif
	TG_CloseTGLibrary(workspace);

	return 0;
}