linedraw.c

C++游戏开发指南

// LINEDRAW.C - General Line Drawing

// Written by Phil Inch for Game Developers Magazine (issue 2).
// Contributed to the public domain.

// This program written and compiled with Borland C++ v3.1
// Compatibility with other compilers is not guaranteed.

// Usage of this program is subject to the disclaimer printed
// in the magazine.  You assume all risks associated with the use
// of this program.

// Note to experienced C programmers: I'm deliberately using 'double'
// instead of 'int' to exaggerate the optimisation.  I don't know if
// other languages optimise integer calculations as well as C does
// so by doing this I hope to present a more general result.



#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <time.h>
#include <dos.h>



// Routine to swap to integers
void swap( int a, int b ) {
	int temp;
	temp = a;
	a = b;
	b = temp;
}


// Routine to put screen into mode 13h
void set_mode_13h( void ) {
	asm {
		mov ax,0x13
		int 0x10
		}
}


// Routine to put screen into mode 3h (text mode)
void set_text_mode( void ) {
	asm {
		mov ax,0x03
		int 0x10
		}
}


// Fast horizontal line drawing program
void fast_horizontal_line( int x1, int x2, int y, unsigned char colour ) {
	char far *screen_location;
	int xcount;

	screen_location = MK_FP( 0xA000, ((int)y*320) + (int)x1 );
	for ( xcount = x1; xcount <= x2; xcount++ ) {
		*screen_location = colour;
		screen_location++;
		}
}

// Fast vertical line drawing program
void fast_vertical_line( int x, int y1, int y2, unsigned char colour ) {
	char far *screen_location;
	int ycount;

	screen_location = MK_FP( 0xA000, (int)x + ((int)y1*320) );
	for ( ycount = y1; ycount <= y2; ycount++ ) {
		*screen_location = colour;
		screen_location += 320;
		}
}


// Pixel plotting routine
void plot_pixel( int x, int y, unsigned char colour ) {
	unsigned char far *screen_position;

	screen_position = MK_FP( 0xA000, x + (320*y) );
	*screen_position = colour;
}


// General line-drawing algorithm
void draw_line( int x1, int y1, int x2, int y2, unsigned char colour ) {
	double xstep, ystep, x, y;
	int xlength, ylength, xcount, ycount;

	xlength = abs( x2 - x1 );
	ylength = abs( y2 - y1 );

	if ( xlength == 0 ) // Vertical Line
		fast_vertical_line( x1, y1, y2, colour );

	else if ( ylength == 0 ) // Horizontal Line
		fast_horizontal_line( x1, x2, y1, colour );

	else if ( xlength > ylength ) {
		if ( x1 > x2 ) {
			swap( x1, x2 );
			swap( y1, y2 );
			}

		ystep = (double)( y2 - y1 ) / (double)( x2 - x1 );
		y = y1;

		for ( xcount = x1; xcount <= x2; xcount++ ) {
			plot_pixel( xcount, (int)y, colour );
			y += ystep;
			}
		}

	else {
		if ( y1 > y2 ) {
			swap( x1, x2 );
			swap( y1, y2 );
			}

		xstep = (double)( x2 - x1 ) / (double)( y2 - y1 );
		x = x1;

		for ( ycount = y1; ycount <= y2; ycount++ ) {
			plot_pixel( (int)x, ycount, colour );
			x += xstep;
			}
		}
}



// This is where the program first starts
void main( void ) {
	int x1, x2, y1, y2;
	long lines, number_of_lines;
	unsigned char colour;
	char input[80];

	clrscr();

	printf( "*** GENERAL LINE DRAWING DEMO ***\n\n" );

	printf( "Suggestions for number of lines:\n\n" );
	printf( "486/50:  25000\n" );
	printf( "486/33:  10000\n" );
	printf( "486/25:   5000\n" );
	printf( "386/40:    500\n" );
	printf( "386/33:    200\n" );
	printf( "lower :    100\n\n" );

	printf( "Enter number of lines to draw: " );
	gets( input );

	number_of_lines = atol(input);
	if ( number_of_lines <= 0 ) {
		printf( "That's not a valid number!" );
		exit(1);
		}

	set_mode_13h();

	for ( lines = 0; lines < number_of_lines; lines++ ) {
		x1 = rand()%320;        // 0 <= x1 <= 319
		y1 = rand()%200;			// 0 <= y1 <= 199
		x2 = rand()%320;        // 0 <= x2 <= 319
		y2 = rand()%200;			// 0 <= y2 <= 199
		colour = rand()%256;		// 0 <= colour <= 255
		draw_line( x1, y1, x2, y2, colour );
		}

	gotoxy( 8, 12 ); puts( "                          " );
	gotoxy( 8, 13 ); puts( " Press <space> to exit... " );
	gotoxy( 8, 14 ); puts( "                          " );
	getch();

	set_text_mode();
}