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* Copyright (c) 1993-2003, Silicon Graphics, Inc.
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* Permission to use, copy, modify, and distribute this software for any
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* purpose and without fee is hereby granted, provided that the above
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* copyright notice appear in all copies and that both the copyright
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* notice and this permission notice appear in supporting documentation,
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* and that the name of Silicon Graphics, Inc. not be used in
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* advertising or publicity pertaining to distribution of the software
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* without specific, written prior permission.
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* THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS" AND
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* WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
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* INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
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* FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL SILICON
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* GRAPHICS, INC. BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
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* SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,
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* OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION, LOSS OF
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* PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF THIRD
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* PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC. HAS BEEN ADVISED OF
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* THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE POSSESSION, USE
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* OR PERFORMANCE OF THIS SOFTWARE.
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* US Government Users Restricted Rights
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* Use, duplication, or disclosure by the Government is subject to
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* restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
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* (c)(1)(ii) of the Rights in Technical Data and Computer Software
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* clause at DFARS 252.227-7013 and/or in similar or successor clauses
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* in the FAR or the DOD or NASA FAR Supplement. Unpublished - rights
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* reserved under the copyright laws of the United States.
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* Contractor/manufacturer is:
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* Silicon Graphics, Inc.
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* 1500 Crittenden Lane
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* Mountain View, CA 94043
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* United State of America
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* OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
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* Compute the histogram of the image. This program illustrates the
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* use of the glHistogram() function.
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#define HISTOGRAM_SIZE 256 /* Must be a power of 2 */
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static GLubyte *pixels;
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static GLsizei width, height;
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static GLuint bswap(GLuint x)
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const GLubyte *ubp = (const GLubyte *) &ui;
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/* we're on little endiang so byteswap x */
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GLsizei y = ((x >> 24)
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| ((x << 8) & 0xff0000)
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| ((x << 24) & 0xff000000));
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readImage( const char* filename, GLsizei* width, GLsizei *height )
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FILE* infile = fopen( filename, "rb" );
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fprintf( stderr, "Unable to open file '%s'\n", filename );
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num_read = fread( width, sizeof( GLsizei ), 1, infile );
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assert(num_read == 1);
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num_read = fread( height, sizeof( GLsizei ), 1, infile );
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assert(num_read == 1);
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*width = bswap(*width);
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*height = bswap(*height);
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n = 3 * (*width) * (*height);
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pixels = (GLubyte *) malloc( n * sizeof( GLubyte ));
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fprintf( stderr, "Unable to malloc() bytes for pixels\n" );
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num_read = fread( pixels, sizeof( GLubyte ), n, infile );
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assert(num_read == n);
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static void init(void)
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if (!glutExtensionSupported("GL_ARB_imaging")) {
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fprintf(stderr, "Sorry, this program requires GL_ARB_imaging.\n");
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glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
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glClearColor(0.0, 0.0, 0.0, 0.0);
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glHistogram(GL_HISTOGRAM, HISTOGRAM_SIZE, GL_RGB, GL_FALSE);
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glEnable(GL_HISTOGRAM);
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static void display(void)
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GLushort values[HISTOGRAM_SIZE][3];
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glClear(GL_COLOR_BUFFER_BIT);
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glDrawPixels(width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels);
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glGetHistogram(GL_HISTOGRAM, GL_TRUE, GL_RGB, GL_UNSIGNED_SHORT, values);
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glBegin(GL_LINE_STRIP);
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glColor3f(1.0, 0.0, 0.0);
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for ( i = 0; i < HISTOGRAM_SIZE; i++ )
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glVertex2s(i, values[i][0]);
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glBegin(GL_LINE_STRIP);
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glColor3f(0.0, 1.0, 0.0);
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for ( i = 0; i < HISTOGRAM_SIZE; i++ )
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glVertex2s(i, values[i][1]);
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glBegin(GL_LINE_STRIP);
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glColor3f(0.0, 0.0, 1.0);
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for ( i = 0; i < HISTOGRAM_SIZE; i++ )
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glVertex2s(i, values[i][2]);
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static void reshape(int w, int h)
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glViewport(0, 0, (GLsizei) w, (GLsizei) h);
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glMatrixMode(GL_PROJECTION);
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glOrtho(0, 256, 0, 10000, -1.0, 1.0);
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glMatrixMode(GL_MODELVIEW);
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static void keyboard(unsigned char key, int x, int y)
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static GLboolean sink = GL_FALSE;
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glHistogram(GL_HISTOGRAM, HISTOGRAM_SIZE, GL_RGB, sink);
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* Open window with initial window size, title bar,
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* RGBA display mode, and handle input events.
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int main(int argc, char** argv)
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pixels = readImage("leeds.bin", &width, &height);
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glutInit(&argc, argv);
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glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
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glutInitWindowSize(width, height);
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glutInitWindowPosition(100, 100);
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glutCreateWindow(argv[0]);
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glutReshapeFunc(reshape);
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glutKeyboardFunc(keyboard);
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glutDisplayFunc(display);