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Why wont this code draw a square?

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Started by thyrgle October 17, 2010 07:34 PM

7 comments, last by empirical2 13 years, 6 months ago

thyrgle

116

Author

October 17, 2010 07:34 PM

#include &lt;iostream&gt;#include &lt;vector&gt;#include &lt;GLUT/GLUT.h&gt;#include &lt;OpenGL/OpenGL.h&gt;#define X_SIZE 640#define Y_SIZE 480class Square {private:public:	Square() {		GLdouble square[] = {			-1.0,  1.0, -1.0,			 1.0,  1.0, -1.0,			 1.0  -1.0, -1.0,			-1.0,  1.0, -1.0		};			glEnableClientState(GL_VERTEX_ARRAY);					glVertexPointer(3, GL_DOUBLE, 0, square);			glDrawArrays(GL_QUADS, 0, 12);					glDisableClientState(GL_VERTEX_ARRAY);	}};void draw() {	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	glEnable(GL_DEPTH_TEST);	Square mySquare;	glutSwapBuffers();}int main (int argc, char **argv) {	glutInit(&argc, argv);	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);	glutInitWindowSize(X_SIZE, Y_SIZE);	glutCreateWindow("Lol");	glutDisplayFunc(draw);	glutMainLoop();    return 0;}

I don't get why this doesn't display a square. I am first initializing glut in int main then, I am drawing the stuff in void draw where I make my object mySquare which by initialization should draw a square. But, I get this weird shaped polygon instead.

Thanks in advance.

XTAL256

106

October 17, 2010 07:59 PM

I do not know why the square will not draw. But you shouldn't be doing the drawing in the object initialisation (constructor). That's not how it's meant to be used. You should have a draw() function in your Square class:

#include <iostream>#include <vector>#include <GLUT/GLUT.h>#include <OpenGL/OpenGL.h>#define X_SIZE 640#define Y_SIZE 480class Square {public:    Square() {}    void draw() {        GLdouble square[] = {            -1.0,  1.0, -1.0,             1.0,  1.0, -1.0,             1.0  -1.0, -1.0,            -1.0,  1.0, -1.0        };        glEnableClientState(GL_VERTEX_ARRAY);        glVertexPointer(3, GL_DOUBLE, 0, square);        glDrawArrays(GL_QUADS, 0, 12);        glDisableClientState(GL_VERTEX_ARRAY);    }};// Define your object here (globally) or elsewhereSquare mySquare;void draw() {    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    glEnable(GL_DEPTH_TEST);    mySquare.draw();    glutSwapBuffers();}...

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karwosts

841

October 17, 2010 08:02 PM

Your 4 vertices do not make a square. Double check your coordinates (where's (-1,-1)?)

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thyrgle

116

Author

October 17, 2010 08:07 PM

Thanks for you help but, it still doesn't work here is my updated code:

[source lang="cpp]#include <iostream>#include <vector>#include <GLUT/GLUT.h>#include <OpenGL/OpenGL.h>#define X_SIZE 640#define Y_SIZE 480class Square {private:public:	Square() {	}	void draw() {        GLdouble square[] = {            -1.0,  1.0, -1.0,			1.0,  1.0, -1.0,			1.0  -1.0, -1.0,            -1.0,  -1.0, -1.0        };        glEnableClientState(GL_VERTEX_ARRAY);        glVertexPointer(3, GL_DOUBLE, 0, square);        glDrawArrays(GL_QUADS, 0, 12);        glDisableClientState(GL_VERTEX_ARRAY);    }	};void draw() {	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	glEnable(GL_DEPTH_TEST);	Square mySquare;	mySquare.draw();	glutSwapBuffers();}int main (int argc, char **argv) {	glutInit(&argc, argv);	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);	glutInitWindowSize(X_SIZE, Y_SIZE);	glutCreateWindow("Lol");	glutDisplayFunc(draw);	glutMainLoop();    return 0;}

swiftcoder

18,997

October 17, 2010 08:17 PM

At least part of the problem is that your vertices are wound clockwise, and OpenGL defaults to counter-clockwise vertex winding. Either order your vertices counter-clockwise, or specify glFrontFace(GL_CW) in your initialisation.

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thyrgle

116

Author

October 17, 2010 08:23 PM

Quote:Original post by swiftcoder
At least part of the problem is that your vertices are wound clockwise, and OpenGL defaults to counter-clockwise vertex winding. Either order your vertices counter-clockwise, or specify glFrontFace(GL_CW) in your initialisation.

Thanks, I have added glFrontFace(GL_CW) before I call mySquare.draw() but, I am still not getting a square. I'm so lost on what to do.

owiley

257

October 17, 2010 08:26 PM

also depending on ur camera settings you might not see the cube that is there. Its because you are either to zoomed in too far or zoomed out too far.

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thyrgle

116

Author

October 17, 2010 08:49 PM

Quote:Original post by owiley
also depending on ur camera settings you might not see the cube that is there. Its because you are either to zoomed in too far or zoomed out too far.

I can see the square if that's what you are referring too.

empirical2

567

October 17, 2010 09:11 PM

glDrawArrays(GL_QUADS, 0, 12);

Should be 4.

Why wont this code draw a square?

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