www.pudn.com > openglbk.rar > blendeqn.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 * Unpublished-- rights reserved under the copyright laws of the 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. 
 */ 
 
/* 
 *  blendeqn.c 
 *  Demonstrate the different blending functions available with the 
 *  OpenGL imaging subset.  This program demonstrates use of the 
 *  glBlendEquation() call. 
 * 
 *  The following keys change the selected blend equation function: 
 * 
 *      'a'  ->  GL_FUNC_ADD 
 *      's'  ->  GL_FUNC_SUBTRACT 
 *      'r'  ->  GL_FUNC_REVERSE_SUBTRACT 
 *      'm'  ->  GL_MIN 
 *      'x'  ->  GL_MAX 
 */ 
 
#include  
#include  
 
 
void init(void) 
{ 
   glClearColor(1.0, 1.0, 0.0, 0.0); 
 
   glBlendFunc(GL_ONE, GL_ONE); 
   glEnable(GL_BLEND); 
} 
 
void display(void) 
{ 
   glClear(GL_COLOR_BUFFER_BIT); 
 
   glColor3f(0.0, 0.0, 1.0); 
   glRectf(-0.5,-0.5,0.5,0.5); 
 
   glFlush(); 
} 
 
void reshape(int w, int h) 
{ 
   GLdouble aspect = (GLdouble) w / h; 
 
   glViewport(0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode(GL_PROJECTION); 
   glLoadIdentity(); 
   if (aspect < 1.0) { 
     aspect = 1.0 / aspect; 
     glOrtho(-aspect, aspect, -1.0, 1.0, -1.0, 1.0); 
   } else 
     glOrtho(-1.0, 1.0, -aspect, aspect, -1.0, 1.0); 
   glMatrixMode(GL_MODELVIEW); 
} 
 
void keyboard(unsigned char key, int x, int y) 
{ 
   switch (key) { 
      case 'a': case 'A': 
	 /* Colors are added as: (1, 1, 0) + (0, 0, 1) = (1, 1, 1) 
	  *  which will produce a white square on a yellow background. 
	  */ 
	 glBlendEquation(GL_FUNC_ADD); 
	 break; 
 
      case 's': case 'S': 
	 /* Colors are subtracted as: (0, 0, 1) - (1, 1, 0) = (-1, -1, 1) 
	  *  which is clamped to (0, 0, 1), producing a blue square on a 
	  *  yellow background 
	  */	 glBlendEquation(GL_FUNC_SUBTRACT); 
	 break; 
 
      case 'r': case 'R': 
	 /* Colors are subtracted as: (1, 1, 0) - (0, 0, 1) = (1, 1, -1) 
	  *  which is clamed to (1, 1, 0).  This produces yellow for both 
	  *  the square and the background. 
	  */ 
	 glBlendEquation(GL_FUNC_REVERSE_SUBTRACT); 
	 break; 
 
      case 'm': case 'M': 
	 /* The minimum of each component is computed, as 
	  *  [min(1, 0), min(1, 0), min(0, 1)] which equates to (0, 0, 0). 
	  *  This will produce a black square on the yellow background. 
	  */ 
	 glBlendEquation(GL_MIN); 
	 break; 
 
      case 'x': case 'X': 
	 /* The minimum of each component is computed, as 
	  *  [max(1, 0), max(1, 0), max(0, 1)] which equates to (1, 1, 1) 
	  *  This will produce a white square on the yellow background. 
	  */ 
	 glBlendEquation(GL_MAX); 
	 break; 
 
      case 27: 
         exit(0); 
   } 
    
   glutPostRedisplay(); 
} 
 
/*  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(512,512); 
   glutInitWindowPosition(100, 100); 
   glutCreateWindow(argv[0]); 
   init(); 
   glutReshapeFunc(reshape); 
   glutKeyboardFunc(keyboard); 
   glutDisplayFunc(display); 
   glutMainLoop(); 
   return 0; 
}