im trying to draw 2 polygons at the same time depending on user input from the opengl screen... so i made 2 arrays which each one of them will carry the vertices of each polygon ... i think my logic is right but the program still prints only polygon and delete the old polygon if you draw a polygon again . and its acting weird too please check the code yourself here it is : P.S dont mind the delete function right now.. i know it missing something. #include <windows.h> #include <gl/gl.h> #include <gl/glut.h> void Draw(); void Set_Transformations(); void Initialize(int argc, char *argv[]); void OnKeyPress(unsigned char key, int x, int y); void DeleteVer(); void MouseClick(int bin, int state , int x , int y); void GetOGLPos(int x, int y,float* arrY,float* arrX); void DrawPolygon(float* arrX,float* arrY); float xPos[20]; float yPos[20]; float xPos2[20]; float yPos2[20]; float fx = 0,fy = 0; float size = 10; int count = 0; bool done = false; bool flag = true; void Initialize(int argc, char *argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGBA); glutInitWindowPosition(100, 100); glutInitWindowSize(600, 600); glutCreateWindow("OpenGL Lab1"); Set_Transformations(); glutDisplayFunc(Draw); glutMouseFunc(MouseClick); glutKeyboardFunc(OnKeyPress); glutMainLoop(); } void Set_Transformations() { glClearColor(1, 1, 1, 1); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(-200, 200, -200, 200); } void OnKeyPress(unsigned char key, int x, int y) { if (key == 27) exit(0); switch(key) { case 13: //enter key it will draw done = true; glutPostRedisplay(); flag=!flag; // this flag to switch to the other array that the vertices will be stored in, in order to draw the second polygon break; } } void MouseClick(int button, int state , int x , int y) { switch (button) { case GLUT_RIGHT_BUTTON: if (state == GLUT_DOWN) { if (count>0) { DeleteVer(); //dont mind this right now } } break; case GLUT_LEFT_BUTTON: if (state == GLUT_DOWN) { if(count<20) { if(flag =true){ // drawing first polygon GetOGLPos(x, y,xPos,yPos);} if (flag=false) //drawing second polygon after Enter is pressed GetOGLPos(x, y,xPos2,yPos2); } } break; } } void GetOGLPos(int x, int y,float* arrY,float* arrX) //getting the vertices from the user { GLint viewport[4]; GLdouble modelview[16]; GLdouble projection[16]; GLfloat winX, winY, winZ; GLdouble posX, posY, posZ; glGetDoublev( GL_MODELVIEW_MATRIX, modelview ); glGetDoublev( GL_PROJECTION_MATRIX, projection ); glGetIntegerv( GL_VIEWPORT, viewport ); winX = (float)x; winY = (float)viewport[3] - (float)y; glReadPixels( x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ ); gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ); arrX[count] = posX; arrY[count] = posY; count++; glPointSize( 6.0 ); glBegin(GL_POINTS); glVertex2f(posX,posY); glEnd(); glFlush(); } void DeleteVer(){ //dont mind this glColor3f ( 1, 1, 1); glBegin(GL_POINTS); glVertex2f(xPos[count-1],yPos[count-1]); glEnd(); glFlush(); xPos[count] = NULL; yPos[count] = NULL; count--; glColor3f ( 0, 0, 0); } void DrawPolygon(float* arrX,float* arrY) { int n=0; glColor3f ( 0, 0, 0); glBegin(GL_POLYGON); while(n<count) { glVertex2f(arrX[n],arrY[n]); n++; } count=0; glEnd(); glFlush(); } void Draw() //main drawing func { glClear(GL_COLOR_BUFFER_BIT); glColor3f(0, 0, 0); if(done) { DrawPolygon(xPos,yPos); DrawPolygon(xPos2,yPos2); } glFlush(); } int main(int argc, char *argv[]) { Initialize(argc, argv); return 0; }