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31 * Unpublished-- rights reserved under the copyright laws of the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 "glut_wrap.h"
45#include <stdlib.h>
46
47static int leftFirst = GL_TRUE;
48
49/*  Initialize alpha blending function.
50 */
51static void init(void)
52{
53   glEnable (GL_BLEND);
54   glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
55   glShadeModel (GL_FLAT);
56   glClearColor (0.0, 0.0, 0.0, 0.0);
57}
58
59static void drawLeftTriangle(void)
60{
61   /* draw yellow triangle on LHS of screen */
62
63   glBegin (GL_TRIANGLES);
64      glColor4f(1.0, 1.0, 0.0, 0.75);
65      glVertex3f(0.1, 0.9, 0.0);
66      glVertex3f(0.1, 0.1, 0.0);
67      glVertex3f(0.7, 0.5, 0.0);
68   glEnd();
69}
70
71static void drawRightTriangle(void)
72{
73   /* draw cyan triangle on RHS of screen */
74
75   glBegin (GL_TRIANGLES);
76      glColor4f(0.0, 1.0, 1.0, 0.75);
77      glVertex3f(0.9, 0.9, 0.0);
78      glVertex3f(0.3, 0.5, 0.0);
79      glVertex3f(0.9, 0.1, 0.0);
80   glEnd();
81}
82
83static void display(void)
84{
85   glClear(GL_COLOR_BUFFER_BIT);
86
87   if (leftFirst) {
88      drawLeftTriangle();
89      drawRightTriangle();
90   }
91   else {
92      drawRightTriangle();
93      drawLeftTriangle();
94   }
95
96   glFlush();
97}
98
99static void reshape(int w, int h)
100{
101   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
102   glMatrixMode(GL_PROJECTION);
103   glLoadIdentity();
104   if (w <= h)
105      gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
106   else
107      gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
108}
109
110/* ARGSUSED1 */
111static void keyboard(unsigned char key, int x, int y)
112{
113   switch (key) {
114      case 't':
115      case 'T':
116         leftFirst = !leftFirst;
117         glutPostRedisplay();
118         break;
119      case 27:  /*  Escape key  */
120         exit(0);
121         break;
122      default:
123         break;
124   }
125}
126
127/*  Main Loop
128 *  Open window with initial window size, title bar,
129 *  RGBA display mode, and handle input events.
130 */
131int main(int argc, char** argv)
132{
133   glutInit(&argc, argv);
134   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
135   glutInitWindowSize (200, 200);
136   glutCreateWindow (argv[0]);
137   init();
138   glutReshapeFunc (reshape);
139   glutKeyboardFunc (keyboard);
140   glutDisplayFunc (display);
141   glutMainLoop();
142   return 0;
143}
144