1/*
2 * Copyright (c) 1993-1997, Silicon Graphics, Inc.
3 * ALL RIGHTS RESERVED
4 * Permission to use, copy, modify, and distribute this software for
5 * any purpose and without fee is hereby granted, provided that the above
6 * copyright notice appear in all copies and that both the copyright notice
7 * and this permission notice appear in supporting documentation, and that
8 * the name of Silicon Graphics, Inc. not be used in advertising
9 * or publicity pertaining to distribution of the software without specific,
10 * written prior permission.
11 *
12 * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
13 * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
14 * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
15 * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
16 * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
17 * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
18 * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
19 * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
20 * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
21 * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
22 * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
23 * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
24 *
25 * US Government Users Restricted Rights
26 * Use, duplication, or disclosure by the Government is subject to
27 * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
28 * (c)(1)(ii) of the Rights in Technical Data and Computer Software
29 * clause at DFARS 252.227-7013 and/or in similar or successor
30 * clauses in the FAR or the DOD or NASA FAR Supplement.
31 * Unpublished-- rights reserved under the copyright laws of the
32 * United States.  Contractor/manufacturer is Silicon Graphics,
33 * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
34 *
35 * OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
36 */
37
38/*
39 *  alpha.c
40 *  This program draws several overlapping filled polygons
41 *  to demonstrate the effect order has on alpha blending results.
42 *  Use the 't' key to toggle the order of drawing polygons.
43 */
44#include <stdlib.h>
45#include <GL/glew.h>
46#include "glut_wrap.h"
47
48static int leftFirst = GL_TRUE;
49
50/*  Initialize alpha blending function.
51 */
52static void init(void)
53{
54   glBlendEquation (GL_FUNC_REVERSE_SUBTRACT);
55   glBlendFunc (GL_ONE_MINUS_SRC_ALPHA, GL_SRC_ALPHA);
56   glShadeModel (GL_FLAT);
57   glClearColor (1.0, 0.0, 0.0, 0.0);
58}
59
60static void drawLeftTriangle(void)
61{
62   /* draw yellow triangle on LHS of screen */
63
64   glBegin (GL_TRIANGLES);
65      glColor4f(1.0, 1.0, 0.0, 0.75);
66      glVertex3f(0.1, 0.9, 0.0);
67      glVertex3f(0.1, 0.1, 0.0);
68      glVertex3f(0.7, 0.5, 0.0);
69   glEnd();
70}
71
72static void drawRightTriangle(void)
73{
74   /* draw cyan triangle on RHS of screen */
75
76   glEnable (GL_BLEND);
77   glBegin (GL_TRIANGLES);
78      glColor4f(0.0, 1.0, 1.0, 0.75);
79      glVertex3f(0.9, 0.9, 0.0);
80      glVertex3f(0.3, 0.5, 0.0);
81      glVertex3f(0.9, 0.1, 0.0);
82   glEnd();
83   glDisable (GL_BLEND);
84}
85
86static void display(void)
87{
88   glClear(GL_COLOR_BUFFER_BIT);
89
90   if (leftFirst) {
91      drawLeftTriangle();
92      drawRightTriangle();
93   }
94   else {
95      drawRightTriangle();
96      drawLeftTriangle();
97   }
98
99   glFlush();
100}
101
102static void reshape(int w, int h)
103{
104   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
105   glMatrixMode(GL_PROJECTION);
106   glLoadIdentity();
107   if (w <= h)
108      gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
109   else
110      gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
111}
112
113/* ARGSUSED1 */
114static void keyboard(unsigned char key, int x, int y)
115{
116   switch (key) {
117      case 't':
118      case 'T':
119         leftFirst = !leftFirst;
120         glutPostRedisplay();
121         break;
122      case 27:  /*  Escape key  */
123         exit(0);
124         break;
125      default:
126         break;
127   }
128}
129
130/*  Main Loop
131 *  Open window with initial window size, title bar,
132 *  RGBA display mode, and handle input events.
133 */
134int main(int argc, char** argv)
135{
136   glutInit(&argc, argv);
137   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
138   glutInitWindowSize (200, 200);
139   glutCreateWindow (argv[0]);
140   glewInit();
141   init();
142   glutReshapeFunc (reshape);
143   glutKeyboardFunc (keyboard);
144   glutDisplayFunc (display);
145   glutMainLoop();
146   return 0;
147}
148