The following program doesn't work:

#include <grx20.h>
#include <grxkeys.h>

#include <stdio.h>

int GRXMain( int argc, char **argv )
{
int x, y;
int maxX, maxY;

GrColor color;
GrContext *context;

GrSetMode( GR_biggest_graphics );
GrSetRGBcolorMode();
GrClearScreen( GrBlack() );

maxX = GrScreenX();
maxY = GrScreenY();

printf("%d %d\n", maxX, maxY );

context = GrCreateContext( maxX, maxY, 0, 0 );
if ( context == 0 )
{
printf("Error creating context\n");
exit(0);
}

GrSetContext( context );

color = GrAllocCell();

for( y=0; y<maxY; y++ )
{
    for( x=0; x<maxX; x++ )
    {
       GrSetColor( color, x, y, 0 );
       GrPlot( x, y, color );
    }
}

GrBitBlt( 0, 0, 0, context, 0, 0 ,maxX, maxY, GrWRITE );
GrDestroyContext( context );
GrFreeColor( color );
GrKeyRead();
return 0;
}

Please tell me why?