OpenGL实现画线-线形-线宽转变

思路：

在画线算法的基础上，添加像素掩膜，&1为1则画否则不画。

// ====== Computer Graphics Experiment #4 ======
// |      Line style using pixel mask          |
// |         and line width                    |  
// =============================================
//
// Requirement:
// (1) Implement a general Bresenham's Line Drawing Algorithm.
// (2) Implement solid, dashed, dotted and dot-dashed line styles 
//     using pixel mask. 
// (3) Implement keyboard function so that the user can switch 
//     line style by pressing a key.
// Only use GL_POINTS drawing mode. 
// Do not use OpenGL line drawing capability.
// Use bit shift statement in C: "<<" or ">>" 
// to implement pixel mask .

#include <windows.h>
#include <GL/glut.h>
#include <math.h>

#define PI 3.14159265359
int width, height;

int line_style=0;
unsigned int pixel_mask[]={0xffff, 0xf0f00, 0xfff0, 0xf00  };
int line_width=1;


void initcor(int &dx, int &dy, int &x, int& y, int &p, int &xs, int &ys, int& xe, int& ye)
{

	dx = xe - xs;
	dy = ye - ys;
	x = xs, y = ys;
	p = 2 * dy - dx;
}
// Bresenham line algorithm
void MyLine(int xs, int ys, int xe, int ye)
{
	// Write your code here
	int dx, dy, x, y, p;
	initcor(dx, dy, x, y, p, xs, ys, xe, ye);
	glBegin(GL_POINTS);
	unsigned int bit_mask = pixel_mask[line_style];
	for (int i = 0; i < dx; ++i)
	{
		bit_mask >>= 1;
		if (!bit_mask)
			bit_mask = pixel_mask[line_style];
		if (bit_mask&1)
		{
			glVertex2i(x, y);
			glVertex2i(y, x);
		}
		++x;
		if (p < 0)
			p += 2 * dy;
		else
		{
			++y; p += 2 * dy - 2 * dx;
		}
	}
	initcor(dx, dy, x, y, p, xs, ys, xe, ye);
	bit_mask = pixel_mask[line_style];
	for (int i = 0; i < dx; ++i)
	{
		bit_mask >>= 1;
		if (!bit_mask)
			bit_mask = pixel_mask[line_style];
		if (bit_mask & 1)
		{
			glVertex2i(x, y);
			glVertex2i(y, x);
		} 
		--x;
		if (p < 0)
			p += 2 * dy;
		else
		{
			--y; p += 2 * dy - 2 * dx;
		}
	}
	initcor(dx, dy, x, y, p, xs, ys, xe, ye); 
	bit_mask = pixel_mask[line_style];
	for (int i = 0; i < dx; ++i)
	{

		bit_mask >>= 1;
		if (!bit_mask)
			bit_mask = pixel_mask[line_style];
		if (bit_mask & 1)
		{
			glVertex2i(x, y);
			glVertex2i(y, x);
		}
		++x;
		if (p < 0)
			p += 2 * dy;
		else
		{
			--y; p += 2 * dy - 2 * dx;
		}
	}
	initcor(dx, dy, x, y, p, xs, ys, xe, ye);
	bit_mask = pixel_mask[line_style];
	for (int i = 0; i < dx; ++i)
	{
		bit_mask >>= 1;
		if (!bit_mask)
			bit_mask = pixel_mask[line_style];
		if (bit_mask & 1)
		{
			glVertex2i(x, y);
			glVertex2i(y, x);
		}
		--x;
		if (p < 0)
			p += 2 * dy;
		else
		{
			++y; p += 2 * dy - 2 * dx;
		}
	}
	glEnd();

}

// Initialization function
void init(void)
{
	glClearColor (0.0, 0.0, 0.0, 0.0);
}

// Display callback function
void display(void)
{
	int i, x0, y0, x, y;
	double a;

	glClear (GL_COLOR_BUFFER_BIT);

	x0=width/2;
	y0=height/2;

	glColor3f(1.0, 1.0, 1.0);

	// Draw lines
	for (i=0; i<360; i+=15)
	{
		a=(double)i/180.0*PI;
		x=0.45*width*cos(a);
		y=0.45*height*sin(a);
		if (i==0 || i==180) y=0;
		if (i==90 || i==270) x=0;
		MyLine(x0, y0, x0 + x, y0 + y);
		for (int j = 1; j < line_width; j++)
		{

			MyLine(x0, y0, x0 + x+j, y0 + y+j);
		}
	}

	glFlush();
}

// Reshape callback function
void reshape(int w, int h)
{
	// Record width and height of program window
	width=w;
	height=h;

	// Set clipping window and viewport equal to
	// view area of program window
	glViewport(0, 0, w, h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D (0.0, w, 0.0, h);
}

// Keyboard callback function
void keyboard(unsigned char key, int x, int y)
{
	switch (key) {
		case 27:
			exit(0);
		case 'q':
			++line_style;
			if (line_style > 3)
				line_style = 0;
			glutPostRedisplay();
			break;
		case 'w':
			++line_width; 
			glutPostRedisplay();
			break;
		// Write your code for line style switching and line width switching
	}
}

// Main program entrance
int main(int argc, char* argv[])
{
	// Create window
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_RGB);
	glutInitWindowSize(500, 500);
	glutCreateWindow("Lines");

	// Initialization
	init();

	// Define callback functions
	glutReshapeFunc(reshape);
	glutKeyboardFunc(keyboard);
	glutDisplayFunc(display);

	// Main program loop. (Event loop)
	glutMainLoop();

	return 0;
}