Resizing glut window

Question

I'm doing 2D drawing in a glut window, and I'm having trouble making the window resize properly.

My glutDisplayFunc and glutReshapeFunc are below. As it is, the drawing disappears when the window is resized. If I delete the glClear() from displayFunc(), new pixels don't "initialize" and there are clipping problems. How do I fix this?

glutDisplayFunc:

void displayFunc() { glDisable( GL_DEPTH_TEST ); glClear( GL_COLOR_BUFFER_BIT ); glPointSize ( 3.0 ); glFlush(); }

glutReshapeFunc:

void windowReshapeFunc( GLint newWidth, GLint newHeight ) { glViewport( 0, 0, newWidth, newHeight ); glMatrixMode( GL_PROJECTION ); glLoadIdentity(); gluOrtho2D( 0, GLdouble (newWidth), 0, GLdouble (newHeight) ); windowWidth = newWidth; windowHeight = newHeight; }

Jerry Coffin · Accepted Answer · 2010-10-06 00:42:55Z

2

I'd try adding a call to glutPostRedisplay() around the end of your reshape function.

answered Oct 6, 2010 at 0:42

Jerry Coffin

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3 Comments

obh Over a year ago

Thanks for the reply, but that doesn't seem to help. Can you explain why you would expect it to?

Jerry Coffin Over a year ago

It causes the display to be updated after the window is resized. Looking more carefully, however, the only actual drawing you have in your display func is clearing the screen, so I wouldn't expect anything else to happen. I'm guessing you have some drawing somewhere else, which really shouldn't be the case.

Amir Zadeh Over a year ago

Diaply IS updated every time reshape is called, that's not the point, obh please post your full code so we can see not guess.

Faruk ERYILMAZ · Accepted Answer · 2017-05-28 18:03:44Z

This is basic template that I use...

#include <GL/glut.h> #include <stdio.h> #include <stdarg.h> #define WINDOW_WIDTH 300 #define WINDOW_HEIGHT 300 // current Window width and height int win_width, win_height; void display() { glClearColor(0, 0, 0, 0); glClear(GL_COLOR_BUFFER_BIT); // write your code here // // glutSwapBuffers(); } void on_resize(int w, int h) { win_width = w; win_height = h; glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-w / 2, w / 2, -h / 2, h / 2, -1, 1); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); display(); // refresh window. } void main(int argc, char *argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE); glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT); glutCreateWindow("basic resize template"); glutDisplayFunc(display); glutReshapeFunc(on_resize); glutMainLoop(); }

CrazyApple · Accepted Answer · 2011-10-16 23:05:20Z

You can not call gluOrtho2D twice with the same window, it will break the graphics and so nothing shows up. You would have to init window size and set Ortho to the size of the screen (current display resolution), then draw relative to the size of the window.

Amir Zadeh · Accepted Answer · 2010-10-11 15:00:56Z

I guess your code does not draw everything on scene in display func, you see, if no events occcur ever you have to call display one time and in the first time it has your drawing. But your problem rises when there is an event which says the window is resized! try putting your drawing part in display function. Like so,

void displayFunc() { glDisable( GL_DEPTH_TEST ); glClear( GL_COLOR_BUFFER_BIT ); glPointSize ( 3.0 ); glBegin(GL_POINTS); { //Blah blah blah some points here which you expect to draw } glEnd(); glFlush(); }

Please post the full code if this was not helpful.

Ryan · Accepted Answer · 2010-10-14 19:04:04Z

You're not setting the matrix mode back to GL_MODELVIEW at the end of your reshape function.

void reshape(int width, int height) { glViewport(0,0,width,height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0, GLdouble (width), 0, GLdouble (height) ); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); }

It's hard to say if there's something else in your display function without seeing more code. I hope that helps.

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