www.pudn.com > openglbk.rar > alpha.c

/* 
 * Copyright (c) 1993-1999, Silicon Graphics, Inc. 
 * ALL RIGHTS RESERVED  
 * Permission to use, copy, modify, and distribute this software for  
 * any purpose and without fee is hereby granted, provided that the above 
 * copyright notice appear in all copies and that both the copyright notice 
 * and this permission notice appear in supporting documentation, and that  
 * the name of Silicon Graphics, Inc. not be used in advertising 
 * or publicity pertaining to distribution of the software without specific, 
 * written prior permission.  
 * 
 * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS" 
 * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE, 
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR 
 * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON 
 * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT, 
 * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY 
 * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION, 
 * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF 
 * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN 
 * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON 
 * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE 
 * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE. 
 *  
 * US Government Users Restricted Rights  
 * Use, duplication, or disclosure by the Government is subject to 
 * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph 
 * (c)(1)(ii) of the Rights in Technical Data and Computer Software 
 * clause at DFARS 252.227-7013 and/or in similar or successor 
 * clauses in the FAR or the DOD or NASA FAR Supplement. 
 * Unpublished-- rights reserved under the copyright laws of the 
 * United States.  Contractor/manufacturer is Silicon Graphics, 
 * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311. 
 * 
 * OpenGL(R) is a registered trademark of Silicon Graphics, Inc. 
 */ 
 
/* 
 *  alpha.c 
 *  This program draws several overlapping filled polygons 
 *  to demonstrate the effect order has on alpha blending results. 
 *  Use the 't' key to toggle the order of drawing polygons. 
 */ 
#include  
#include  
 
static int leftFirst = GL_TRUE; 
 
/*  Initialize alpha blending function. 
 */ 
static void init(void) 
{ 
   glEnable (GL_BLEND); 
   glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
   glShadeModel (GL_FLAT); 
   glClearColor (0.0, 0.0, 0.0, 0.0); 
} 
 
static void drawLeftTriangle(void) 
{ 
   /* draw yellow triangle on LHS of screen */ 
 
   glBegin (GL_TRIANGLES); 
      glColor4f(1.0, 1.0, 0.0, 0.75); 
      glVertex3f(0.1, 0.9, 0.0);  
      glVertex3f(0.1, 0.1, 0.0);  
      glVertex3f(0.7, 0.5, 0.0);  
   glEnd(); 
} 
 
static void drawRightTriangle(void) 
{ 
   /* draw cyan triangle on RHS of screen */ 
 
   glBegin (GL_TRIANGLES); 
      glColor4f(0.0, 1.0, 1.0, 0.75); 
      glVertex3f(0.9, 0.9, 0.0);  
      glVertex3f(0.3, 0.5, 0.0);  
      glVertex3f(0.9, 0.1, 0.0);  
   glEnd(); 
} 
 
void display(void) 
{ 
   glClear(GL_COLOR_BUFFER_BIT); 
 
   if (leftFirst) { 
      drawLeftTriangle(); 
      drawRightTriangle(); 
   } 
   else { 
      drawRightTriangle(); 
      drawLeftTriangle(); 
   } 
 
   glFlush(); 
} 
 
void reshape(int w, int h) 
{ 
   glViewport(0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode(GL_PROJECTION); 
   glLoadIdentity(); 
   if (w <= h)  
      gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w); 
   else  
      gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0); 
} 
 
void keyboard(unsigned char key, int x, int y) 
{ 
   switch (key) { 
      case 't': 
      case 'T': 
         leftFirst = !leftFirst; 
         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; 
}