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copied!<p>Please take a look at the following example, taken from here: <a href="http://seriss.com/people/erco/fltk/#OpenGlInterp" rel="nofollow">http://seriss.com/people/erco/fltk/#OpenGlInterp</a></p> <pre><code>#include <FL/Fl.H> #include <FL/Fl_Gl_Window.H> #include <FL/gl.h> #include <math.h> // // Demonstrate interpolating shapes // erco 06/10/05 // class Playback : public Fl_Gl_Window { int frame; // Linear interpolation between two values based on 'frac' (0.0=a, 1.0=b) float Linterp(float frac, float a, float b) { return( a + ( frac * (b - a) )); } // Sinusoidal easein/easeout interpolation between two values based on 'frac' (0.0=a, 1.0=b) float SinInterp(float frac, float a, float b) { float pi = 3.14159; frac = (sin(pi/2 + frac*pi ) + 1.0 ) / 2.0; // 0 ~ 1 -> 0 ~ 1 return(Linterp(frac,a,b)); } // DRAW SIMPLE SHAPE INTERPOLATION // Interpolation is based on the current frame number // void DrawShape(int frame) { // Calculate a fraction that represents the frame# being shown float frac = ( frame % 48 ) / 48.0 * 2; if ( frac > 1.0 ) frac = 2.0-frac; // saw tooth wave: "/\/\/\" static float a_xy[9][2] = { { -.5, -1. }, { 0.0, -.5 }, { -.5, -1. }, { 0.0, -.5 }, { 0.0, 0.0 }, { 0.0, -.5 }, { +.5, -1. }, { 0.0, -.5 }, { +.5, -1. }, }; static float b_xy[9][2] = { { -.25, -1. }, { -.50, -.75 }, { -.75, -1.0 }, { -.50, -.75 }, { 0.0, 0.0 }, { +.50, -.75 }, { +.75, -1.0 }, { +.50, -.75 }, { +.25, -1.0 } }; // Linterp a and b to form new shape c float c_xy[9][2]; for ( int i=0; i<9; i++ ) for ( int xy=0; xy<2; xy++ ) c_xy[i][xy] = SinInterp(frac, a_xy[i][xy], b_xy[i][xy]); // Draw shape glColor3f(1.0, 1.0, 1.0); glBegin(GL_LINE_STRIP); for ( int i=0; i<9; i++ ) glVertex2f(c_xy[i][0], c_xy[i][1]); glEnd(); } // DRAW THE WIDGET // Each time we're called, assume // void draw() { if (!valid()) { valid(1); glLoadIdentity(); glViewport(0,0,w(),h()); } glClear(GL_COLOR_BUFFER_BIT); // Draw shape 4x, rotated at 90 degree positions glPushMatrix(); DrawShape(frame); glRotatef(90.0, 0, 0, 1); DrawShape(frame); glRotatef(90.0, 0, 0, 1); DrawShape(frame); glRotatef(90.0, 0, 0, 1); DrawShape(frame); glPopMatrix(); // Advance frame counter ++frame; } // 24 FPS TIMER CALLBACK // Called 24x per second to redraw the widget // static void Timer_CB(void *userdata) { Playback *pb = (Playback*)userdata; pb->redraw(); Fl::repeat_timeout(1.0/24.0, Timer_CB, userdata); } public: // Constructor Playback(int X,int Y,int W,int H,const char*L=0) : Fl_Gl_Window(X,Y,W,H,L) { frame = 0; Fl::add_timeout(1.0/24.0, Timer_CB, (void*)this); // 24fps timer end(); } }; int main() { Fl_Window win(500, 500); Playback playback(10, 10, win.w()-20, win.h()-20); win.resizable(&playback); win.show(); return(Fl::run()); } </code></pre> <p>This example more/less does exactly what you want. Greg Ercolano has more FLTK examples on his web-site. I recommend taking a look at <a href="http://seriss.com/people/erco/fltk/" rel="nofollow">http://seriss.com/people/erco/fltk/</a> .</p>

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