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POopengl dynamic bezier curve has gaps - glEvalCoord1f();
 

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  1. POopengl dynamic bezier curve has gaps - glEvalCoord1f();
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    <p>I like to have a program where you can pick ten points and then a bezier curve is calculated for that points. It seems to work pretty perfect, but the shown curve has some gaps. I used <code>GL_LINE_STRIP</code> how is it possible that the points are not connected?</p> <p>I figured out, that a very small <code>u</code> in <code>glEvalCoord1f(u);</code> makes the gaps smaller. How is <code>u</code> depending on controlpoints and window propperties in <code>glEvalCoord1f(u);</code> ?</p> <p><img src="https://i.stack.imgur.com/zCQtO.png" alt="Beziere gaps Line width 1"></p> <p>[Edit] Added Screen with thicker lines: <img src="https://i.stack.imgur.com/oCaoW.png" alt="Beziere gaps Line width 3"></p> <pre><code>#include &lt;iostream&gt; #include &lt;stdlib.h&gt; #include &lt;string&gt; #include &lt;fstream&gt; #include &lt;math.h&gt; #include &lt;time.h&gt; #include &lt;GL/glut.h&gt; //added GL prefix for Ubuntu compatibility #define MAXP 10 GLint nNumPoints = 0; GLfloat ctrlpoints[10][3]; GLdouble mouseOgl[3] = {0.0,0.0,0.0}; GLint mouseX, mouseY; bool mousePressed = false; void GetOGLPos(int x, int y); void init(void) { glClearColor(1.0, 1.0, 1.0, 0.0); glShadeModel(GL_FLAT); // Enable the evaluator glEnable(GL_MAP1_VERTEX_3); glEnable(GL_DEPTH); } void display(void) { int i; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glColor3f(0.0, 0.0, 1.0); if(mousePressed &amp;&amp; nNumPoints &lt; MAXP){ GetOGLPos(mouseX, mouseY); std::cout &lt;&lt; mouseOgl[0] &lt;&lt; " # " &lt;&lt; mouseOgl[1] &lt;&lt; " # " &lt;&lt; mouseOgl[2] &lt;&lt; " # " &lt;&lt; std::endl; nNumPoints++; ctrlpoints[nNumPoints-1][0] = mouseOgl[0]; ctrlpoints[nNumPoints-1][3] = mouseOgl[1]; ctrlpoints[nNumPoints-1][2] = mouseOgl[2]; } //Curves if( nNumPoints == MAXP ){ glMap1f(GL_MAP1_VERTEX_3, // Type of data generated 0.0f, // Lower u range 1.0f, // Upper u range 3, // Distance between points in the data 3: ...Z-X-Y-Z... nNumPoints, // number of control points &amp;ctrlpoints[0][0]); // start point glBegin(GL_LINE_STRIP); float max = pow(MAXP,4)*2; //accuracy of pint calulation? for (i = 0; i &lt;= max; i++) glEvalCoord1f((GLfloat) (i/max)); //high value to avoid gaps?!? glEnd(); } //Controllpoints: glPointSize(5.0); glColor3f(1.0, 0.0, 0.0); glBegin(GL_POINTS); for (i = 0; i &lt; nNumPoints; i++) glVertex3fv(&amp;ctrlpoints[i][0]); glEnd(); //Lines glColor3f(0.0, 1.0, 0.0); glBegin(GL_LINE_STRIP); for (i = 0; i &lt; nNumPoints; i++) glVertex3fv(&amp;ctrlpoints[i][0]); glEnd(); if( nNumPoints == MAXP ){nNumPoints = 0;} glFlush(); } void reshape(int w, int h) { glViewport(0, 0, (GLsizei) w, (GLsizei) h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); //keep aspect ratio: if (w &lt;= h) glOrtho(-2.0, 2.0, -2.0*(GLfloat)h/(GLfloat)w, 2.0*(GLfloat)h/(GLfloat)w, -2.0, 2.0); else glOrtho(-2.0*(GLfloat)w/(GLfloat)h, 2.0*(GLfloat)w/(GLfloat)h, -2.0, 2.0, -2.0, 2.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } //handle click events of the mouse void myMouse(int button, int state, int x, int y) { //mouse coords to gl coords mouseX = x; mouseY = y; switch (button) { case GLUT_LEFT_BUTTON: if(state == GLUT_UP){ //on release left mouse button std::cout &lt;&lt; x &lt;&lt; " * "&lt;&lt; y &lt;&lt; std::endl; mousePressed = true; glutPostRedisplay(); //redisplay and calculate gl coords } else { mousePressed = false; } break; } } // detailed information: // http://nehe.gamedev.net/article/using_gluunproject/16013/ void GetOGLPos(int x, int y) { //init vars: GLint viewport[4]; GLdouble modelview[16]; GLdouble projection[16]; GLfloat winX, winY, winZ; GLdouble posX, posY, posZ; //get gl specs glGetDoublev( GL_MODELVIEW_MATRIX, modelview ); //get Modelmatrix glGetDoublev( GL_PROJECTION_MATRIX, projection ); //get projection matrix glGetIntegerv( GL_VIEWPORT, viewport ); //get viewport values //calculate the gl mouseposition winX = (float)x; winY = (float)viewport[3] - (float)y; glReadPixels( x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &amp;winZ ); gluUnProject( winX, winY, winZ, modelview, projection, viewport, &amp;posX, &amp;posY, &amp;posZ); mouseOgl[0] = posX; mouseOgl[1] = posY; mouseOgl[2] = posZ; } int main(int argc, char** argv) { glutInit(&amp;argc, argv); glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (600, 600); glutInitWindowPosition (100, 100); glutCreateWindow (argv[0]); init (); glutDisplayFunc(display); glutReshapeFunc(reshape); glutMouseFunc(myMouse); glutMainLoop(); return 0; } </code></pre>
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      1. VTFavorite
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    1. COscreen provided, to make it clearer on sceen I changed "float max = pow(MAXP,4)*2;" to "float max = pow(MAXP,2)*2;"
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    2. COcan you increase the size of the blue line?
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      1. USStephen D
    3. COI can, but it does not solve the problem. Or do you need it as screen?
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