--- /dev/null
+/*
+ * freeglut offscreen rendering demo.
+ *
+ * Usage:
+ *
+ * offscreen [standard GLUT options] [filename]
+ *
+ * The filename is used to say where to write a PNM image file
+ * that is the sole way to verify that this program is doing what
+ * it should (i.e., rendering offscreen).
+ *
+ * You can view the PNM file in image viewers and editors such as
+ * the GIMP. (Everyone doing any kind of graphics has at least one
+ * multi-format-reading image manipulation program, right?)
+ *
+ * If no filename is specified, the chosen filename is "offscreen.pnm".
+ *
+ * Some suggested uses for GLUT_OFFSCREEN:
+ *
+ * * Implementation of a graphics language that writes bitmapped image files.
+ * * Capture GLUT bitmapped fonts to a texture at runtime to make scalable
+ * bitmapped fonts.
+ * * Using OpenGL to create special-effect textures at run-time.
+ * * Making stencils.
+ * * Getting the depth-buffer for a height-field.
+ * * Using OpenGL to create a poster texture (e.g., for pasting onto a a
+ * video screen in a virtual world).
+ * * Using OpenGL to prescale an image to a power-of-2 dimension (including
+ * OpenGL antialiasing). There's no reason that you couldn't do this
+ * yourself, but OpenGL can do it for you, so why not?
+ * * Rendering to a bitmap larger than the display has been suggested
+ * as well. This is a cheap way to produce arbitrarily high resolution
+ * images for printing.
+ *
+ * In every case, there are at least cases where you would want to do this
+ * without actually rendering to a visible window.
+ *
+ */
+#include <stdio.h>
+#include <GL/freeglut.h>
+
+#define OFFSCREEN_W 500
+#define OFFSCREEN_H 250
+
+
+int offscreen_id;
+int onscreen_id;
+const char *save_file_name = "offscreen.pnm";
+
+
+void cb_onscreen_display( void )
+{
+ glClear( GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT );
+ glColor3d( 1.0, 0.0, 0.0 );
+ glBegin( GL_LINE_LOOP );
+ glVertex2d( 0.0, 0.0 );
+ glVertex2d( 0.5, 0.0 );
+ glVertex2d( 0.5, 0.5 );
+ glVertex2d( 0.0, 0.5 );
+ glVertex2d( 0.0, 0.0 );
+ glEnd( );
+ glColor3d( 1.0, 1.0, 1.0 );
+ glRasterPos2d( -1.0, 0.8 );
+ glutBitmapString(
+ GLUT_BITMAP_TIMES_ROMAN_24, "Press `s' or `S' to Send to"
+ );
+ glRasterPos2d( -.8, 0.6 );
+ glutBitmapString(
+ GLUT_BITMAP_TIMES_ROMAN_24, "'offscreen.pnm'"
+ );
+ glRasterPos2d( -1.0, 0.3 );
+ glutBitmapString(
+ GLUT_BITMAP_TIMES_ROMAN_24, "Press `q', `Q', or Esc to quit."
+ );
+
+ glutSwapBuffers( );
+}
+
+void write_raw_pnm( char *fname, char *pixels, int w, int h)
+{
+ FILE *f;
+
+ printf( "Trying to create: %s\n", fname );
+ f = fopen( fname, "wb" );
+ if( !f )
+ printf( "Ouch! Cannot create file.\n" );
+ else
+ {
+ int row;
+
+ printf( "Opened file.\n" );
+ fprintf( f, "P6\n" );
+ fprintf( f, "# CREATOR: offscreen freeglut demo\n" );
+ fprintf( f, "%d %d\n", w, h );
+ fprintf( f, "255\n" );
+
+ /*
+ * Write the rows in reverse order because OpenGL's 0th row
+ * is at the bottom.
+ */
+ for( row = h; row; --row )
+ fwrite( pixels + ((row - 1)*w*3), 1, 3 * w, f );
+
+ fclose( f );
+ }
+}
+
+
+void cb_offscreen_display( void )
+{
+ static char pixels [OFFSCREEN_W * OFFSCREEN_H * 3];
+ int i;
+
+ cb_onscreen_display( );
+ glColor3d( 0.0, 1.0, 0.0 );
+ glBegin( GL_LINES );
+ for( i = 0; i < 100; ++i)
+ {
+ glVertex2d( +1 - (i/50.0), +1 );
+ glVertex2d( -1 + (i/50.0), -1 );
+ }
+ glEnd( );
+ glFinish( );
+
+ glPixelStorei( GL_PACK_ALIGNMENT, 1 );
+ glReadPixels(
+ 0, 0, OFFSCREEN_W, OFFSCREEN_H,
+ GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)pixels
+ );
+ write_raw_pnm( save_file_name, pixels, OFFSCREEN_W, OFFSCREEN_H );
+}
+
+
+void cb_onscreen_keyboard( unsigned char key, int x, int y )
+{
+ switch( key )
+ {
+ case 's':
+ case 'S':
+ glutSetWindow( offscreen_id );
+ glutPostRedisplay( );
+ break;
+
+ case '\x1b':
+ case 'q':
+ case 'Q':
+ exit( 0 );
+ break;
+
+ default:
+ break;
+ }
+}
+
+int main( int argc, char **argv )
+{
+ glutInit( &argc, argv );
+ if( argv[ 1 ] )
+ save_file_name = argv[ 1 ];
+
+ glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE );
+ onscreen_id = glutCreateWindow( "Offscreen demo" );
+ glutDisplayFunc( cb_onscreen_display );
+ glutKeyboardFunc( cb_onscreen_keyboard );
+
+ glutInitDisplayMode( GLUT_RGB | GLUT_SINGLE | GLUT_OFFSCREEN );
+ glutInitWindowSize( OFFSCREEN_W, OFFSCREEN_H );
+ offscreen_id = glutCreateWindow( "" );
+ glutDisplayFunc( cb_offscreen_display );
+
+ glutMainLoop( );
+}
projects / freeglut / commitdiff