opengl中的抗锯齿

opengl的抗锯齿

1.对直线和点主要用函数GL_Enable(GL_LINE_SMOOTH)或GL_Enable(GL_POINT_SMOOTH)

2.对RGBA模式需要启动混合功能,最常用的混合模式为GL_SRC_ALPHA和GL_ONE_MINUS_SRC_ALPHA(用GL_Blend开启混合模式)

以下摘自OPENGL编程指南的aargb.c代码

/*
 *  aargb.c
 *  This program draws shows how to draw anti-aliased lines. It draws
 *  two diagonal lines to form an X; when 'r' is typed in the window,
 *  the lines are rotated in opposite directions.
 */

#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>

static float rotAngle = 0.;

/*  Initialize antialiasing for RGBA mode, including alpha
 *  blending, hint, and line width.  Print out implementation
 *  specific info on line width granularity and width.
 */
void init(void)
{
   GLfloat values[2];
   glGetFloatv (GL_LINE_WIDTH_GRANULARITY, values);
   printf ("GL_LINE_WIDTH_GRANULARITY value is %3.1f\n", values[0]);

   glGetFloatv (GL_LINE_WIDTH_RANGE, values);
   printf ("GL_LINE_WIDTH_RANGE values are %3.1f %3.1f\n",
      values[0], values[1]);

   glEnable (GL_LINE_SMOOTH);
   glEnable (GL_BLEND);
   glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
   glHint (GL_LINE_SMOOTH_HINT, GL_DONT_CARE);
   glLineWidth (1.5);

   glClearColor(0.0, 0.0, 0.0, 0.0);
}

/* Draw 2 diagonal lines to form an X
 */
void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT);

   glColor3f (0.0, 1.0, 0.0);
   glPushMatrix();
   glRotatef(-rotAngle, 0.0, 0.0, 0.1);
   glBegin (GL_LINES);
      glVertex2f (-0.5, 0.5);
      glVertex2f (0.5, -0.5);
   glEnd ();
   glPopMatrix();

   glColor3f (0.0, 0.0, 1.0);
   glPushMatrix();
   glRotatef(rotAngle, 0.0, 0.0, 0.1);
   glBegin (GL_LINES);
      glVertex2f (0.5, 0.5);
      glVertex2f (-0.5, -0.5);
   glEnd ();
   glPopMatrix();

   glFlush();
}

void reshape(int w, int h)
{
   glViewport(0, 0, w, h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      gluOrtho2D (-1.0, 1.0,
         -1.0*(GLfloat)h/(GLfloat)w, 1.0*(GLfloat)h/(GLfloat)w);
   else
      gluOrtho2D (-1.0*(GLfloat)w/(GLfloat)h,
         1.0*(GLfloat)w/(GLfloat)h, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 'r':
      case 'R':
         rotAngle += 20.;
         if (rotAngle >= 360.) rotAngle = 0.;
         glutPostRedisplay(); 
         break;
      case 27:  /*  Escape Key  */
         exit(0);
         break;
      default:
         break;
    }
}

/*  Main Loop
 *  Open window with initial window size, title bar,
 *  RGBA display mode, and handle input events.
 */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (200, 200);
   glutCreateWindow (argv[0]);
   init();
   glutReshapeFunc (reshape);
   glutKeyboardFunc (keyboard);
   glutDisplayFunc (display);
   glutMainLoop();
   return 0;
}