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31 * Unpublished-- rights reserved under the copyright laws of the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
47 static int leftFirst = GL_TRUE;
48
49 /* Initialize alpha blending function.
50 */
init(void)51 static void init(void)
52 {
53 glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
54 glShadeModel (GL_FLAT);
55 glClearColor (1.0, 0.0, 0.0, 1.0);
56 }
57
drawLeftTriangle(void)58 static void drawLeftTriangle(void)
59 {
60 /* draw yellow triangle on LHS of screen */
61
62 glBegin (GL_TRIANGLES);
63 glColor4f(1.0, 1.0, 0.0, 0.75);
64 glVertex3f(0.1, 0.9, 0.0);
65 glVertex3f(0.1, 0.1, 0.0);
66 glVertex3f(0.7, 0.5, 0.0);
67 glEnd();
68 }
69
drawRightTriangle(void)70 static void drawRightTriangle(void)
71 {
72 /* draw cyan triangle on RHS of screen */
73
74 glEnable (GL_BLEND);
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 glDisable (GL_BLEND);
82 }
83
display(void)84 static void display(void)
85 {
86 glClear(GL_COLOR_BUFFER_BIT);
87
88 if (leftFirst) {
89 drawLeftTriangle();
90 drawRightTriangle();
91 }
92 else {
93 drawRightTriangle();
94 drawLeftTriangle();
95 }
96
97 glFlush();
98 }
99
reshape(int w,int h)100 static void reshape(int w, int h)
101 {
102 glViewport(0, 0, (GLsizei) w, (GLsizei) h);
103 glMatrixMode(GL_PROJECTION);
104 glLoadIdentity();
105 if (w <= h)
106 gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
107 else
108 gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
109 }
110
111 /* ARGSUSED1 */
keyboard(unsigned char key,int x,int y)112 static void keyboard(unsigned char key, int x, int y)
113 {
114 switch (key) {
115 case 't':
116 case 'T':
117 leftFirst = !leftFirst;
118 glutPostRedisplay();
119 break;
120 case 27: /* Escape key */
121 exit(0);
122 break;
123 default:
124 break;
125 }
126 }
127
128 /* Main Loop
129 * Open window with initial window size, title bar,
130 * RGBA display mode, and handle input events.
131 */
main(int argc,char ** argv)132 int main(int argc, char** argv)
133 {
134 glutInit(&argc, argv);
135 glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_ALPHA);
136 glutInitWindowSize (200, 200);
137 glutCreateWindow (argv[0]);
138 init();
139 glutReshapeFunc (reshape);
140 glutKeyboardFunc (keyboard);
141 glutDisplayFunc (display);
142 glutMainLoop();
143 return 0;
144 }
145