1 files changed, 145 insertions, 0 deletions
diff --git a/progs/trivial/tri-blend-revsub.c b/progs/trivial/tri-blend-revsub.c
new file mode 100644
index 0000000000..be187fd4ce
--- /dev/null
+++ b/progs/trivial/tri-blend-revsub.c
@@ -0,0 +1,145 @@
+/*
+ * Copyright (c) 1993-1997, 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+ * Unpublished-- rights reserved under the copyright laws of the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 <GL/glut.h>
+#include <stdlib.h>
+
+static int leftFirst = GL_TRUE;
+
+/*  Initialize alpha blending function.
+ */
+static void init(void)
+{
+   glBlendEquation (GL_FUNC_REVERSE_SUBTRACT);
+   glBlendFunc (GL_ONE_MINUS_SRC_ALPHA, GL_SRC_ALPHA);
+   glShadeModel (GL_FLAT);
+   glClearColor (1.0, 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 */
+
+   glEnable (GL_BLEND);
+   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();
+   glDisable (GL_BLEND);
+}
+
+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);
+}
+
+/* ARGSUSED1 */
+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;
+}