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new-bie needs help

Started by rick_st3 Jun 18, 2008 at 4:07 AM 20 replies 2.3k views

Original Post

Jun 18, 2008 at 4:07 AM

Alright... I have just started learning opengl a week ago and am in a problem...i wrote a code to rotate a 3d cube on the vector (1.0f,1.0f,1.0f)...The cube does rotate on the axis but,well,it does not look like a cube..it looks something else.. Here are the coordinates which i plotted... glBegin(GL_QUADS); glColor3f(1.0f,1.0f,0.0f); glVertex3f(0.25f,0.25f,-0.25f); glVertex3f(-0.25f,0.25f,-0.25f); glVertex3f(-0.25f,0.25f,0.25f); //top glVertex3f(0.25f,0.25f,0.25f); glColor3f(0.0f,1.0f,0.0f); glVertex3f(-0.25f,0.25f,0.25f); glVertex3f(-0.25f,0.25f,-0.25f); glVertex3f(-0.25f,-0.25f,-0.25f); glVertex3f(-0.25f,-0.25f,0.25f); //left glColor3f(1.0f,0.0f,0.0f); glVertex3f(0.25f,-0.25f,-0.25f); glVertex3f(-0.25f,-0.25f,-0.25f); glVertex3f(-0.25f,0.25f,-0.25f); //back glVertex3f(0.25f,0.25f,-0.25f); glColor3f(0.0f,0.0f,1.0f); glVertex3f(-0.25f,-0.25f,0.25f); glVertex3f(-0.25f,-0.25f,-0.25f); glVertex3f(0.25f,-0.25f,-0.25f); //bottom glVertex3f(0.25f,-0.25f,0.25f); glColor3f(1.0f,0.0f,1.0f); glVertex3f(-0.25f,0.25f,0.25f); glVertex3f(-0.25f,-0.25f,0.25f); glVertex3f(0.25f,-0.25f,0.25f); glVertex3f(0.25f,0.25f,0.25f); //front glColor3f(0.0f,1.0f,1.0f); glVertex3f(0.25f,0.25f,-0.25f); glVertex3f(0.25f,0.25f,0.25f); glVertex3f(0.25f,-0.25f,0.25f); glVertex3f(0.25f,-0.25f,-0.25f); //right during the rotation when the bottom,front and right faces come towards the front only then it resembles a cube i.e. only den you can see three colors/face or else for all other positions there are more then 3 colors which makes the window a mess... please help..!!!

zimerman

Jun 18, 2008 at 8:44 AM

glEnable( GL_DEPTH_TEST ); !?

Arkaras

Jun 18, 2008 at 8:44 AM

Its actually working perfectly. In order to not have this problem,you will need to turn on depth testing when you initialize your Opengl Context. Otherwise Opengl has no clue what side you want to look at. But in fact it is correctly being drawn, without depth testing.

Arkaras

Jun 18, 2008 at 8:46 AM

Quote:
Original post by zimerman
glEnable( GL_DEPTH_TEST ); !?

Enabling depth testing should normally happen in your Opengl context set up as well.

rick_st3

Jun 18, 2008 at 11:04 AM

alright here goes my initialize function

GLvoid ric::glInitialize()
{
glClearColor(0.0f,0.0f,0.0f,0.0f);
glShadeModel(GL_SMOOTH);
glClearDepth(1.0f);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

rquad = 0.0f;
}

now inspite of my enabling the depth testing m facing this problem...
Also do I have to imply display lists in order to get a complete rotating cube view..??

oh yes...i am using opengl with Qt actually...

rick_st3

Jun 19, 2008 at 12:40 AM

And also i would like to know whether it is possible to paint the entire cube with the same color,say green, with just the edges having a different color,say black..?? thanks...

Lord_Evil

Jun 19, 2008 at 3:14 AM

Drawing a green cube with black edges would require to draw the cube twice (if you don't use textures or shaders). So you basically draw the green cube (all vertices green) in fill mode and then change the color to black and either draw the quads in wireframe mode (which might give you diagonal lines if the quads are split into triangles by the driver) or draw the edges as individual lines. Just remember to change the depth comparison mode to GL_EQUAL or GL_LEQUAL, so that the lines drawn on top of the quad pass the depth test (they basically have the same depth as the quads).

Edit: Ah, I just reread your code. Where do those additional color appear? If only at the edges it could be due to GL_LEQUAL since at the edges the fragments produces by two quads might have the same depth.

rick_st3

Jun 20, 2008 at 3:12 AM

no actually the colors of the bottom three faces seem to overlap all the other colors even if one of the bottom three faces was supposed to b on the back side in that instance... and also if the bottom three faces overlap each other then the one latter included is on the top even if it is not supposed to be...

Lord_Evil

Jun 20, 2008 at 3:29 AM

I think it would be the best if you showed us some screen shots so we can see what's going on.

rick_st3

Jun 20, 2008 at 8:44 AM

alright here is when the cube looks like one....

and here are the other views...

and...

rick_st3

Jun 20, 2008 at 8:47 AM

now the colors might me different as i tried varying their sequence and colors...

dmatter

Jun 20, 2008 at 10:26 AM

Hopefully a silly question, but do you make sure to call both glEnd() and glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) each and every frame?
Also, if you were using the win32 API, you'd have to make sure to state the number of bits for the depth buffer - make sure you do whatever the equivalent is with Qt.

rick_st3

Jun 20, 2008 at 10:48 AM

i have used an update() statement after glEnd()in Qt...that is equivalent to calling the same paint function recursively... and the paint function starts off with a glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) statement...

dmatter

Jun 20, 2008 at 10:56 AM

Another thought, have you got front/back face culling enabled?

rick_st3

Jun 21, 2008 at 12:56 AM

no i hadn't enabled that option initially but the i tried enabling it in the glInitialize() but then again the problem remains the same..!!

Lord_Evil

Jun 21, 2008 at 10:47 AM

Could you please post the relevant update and drawing functions? Take care to use the [ source] and [ /source ] tags (without the spaces).

rick_st3

Jun 23, 2008 at 2:04 AM

alright here goes my paint function

GLvoid ric::paintGL(){	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	glLoadIdentity();	glRotatef(rx,1.0,1.0,1.0);//	glRotatef(ry,0.0,1.0,1.0);//	glRotatef(rz,0.0,0.0,1.0);	glOrtho(-2.0,2.0,-2.0,2.0,-2.0,2.0);	glBegin(GL_QUADS);				glColor3f(0.0f,0.0f,1.0f);		glVertex3f(-1.0f,-1.0f,1.0f);		glVertex3f(1.0f,-1.0f,1.0f);		glVertex3f(1.0f,-1.0f,-1.0f);			//deep blue bottom		glVertex3f(-1.0f,-1.0f,-1.0f);		glColor3f(1.0f,0.0f,1.0f);		glVertex3f(-1.0f,1.0f,1.0f);		glVertex3f(-1.0f,-1.0f,1.0f);		glVertex3f(1.0f,-1.0f,1.0f);		glVertex3f(1.0f,1.0f,1.0f);				// pink front		glColor3f(0.0f,1.0f,1.0f);		glVertex3f(1.0f,-1.0f,-1.0f);			//sky blue right		glVertex3f(1.0f,1.0f,-1.0f);		glVertex3f(1.0f,1.0f,1.0f);		glVertex3f(1.0f,-1.0f,1.0f);		glColor3f(1.0f,1.0f,0.0f);		glVertex3f(-1.0f,1.0f,-1.0f);		glVertex3f(1.0f,1.0f,-1.0f);		glVertex3f(1.0f,1.0f,1.0f);		glVertex3f(-1.0f,1.0f,1.0f);				// yellow top		glColor3f(1.0f,0.0f,0.0f);		glVertex3f(1.0f,1.0f,-1.0f);		glVertex3f(1.0f,-1.0f,-1.0f);		glVertex3f(-1.0f,-1.0f,-1.0f);		glVertex3f(-1.0f,1.0f,-1.0f);			//red back		glColor3f(0.0f,1.0f,0.0f);		glVertex3f(-1.0f,1.0f,-1.0f);		glVertex3f(-1.0f,-1.0f,-1.0f);		glVertex3f(-1.0f,-1.0f,1.0f);			//green	left		glVertex3f(-1.0f,1.0f,1.0f);	glEnd();	rx += 0.05f;	ry += 0.05f;	rz += 0.05f;	update();}

now what the update function does in Qt is calls the PaintGL() function automatically...

stefanborries

Jun 23, 2008 at 3:32 AM

Seems you have some sides wrong (back/front), I'm not sure which. You better take a look at the sides.

Lord_Evil

Jun 23, 2008 at 10:18 AM

Assuming the current matrix mode is GL_MODELVIEW that glOrtho(-2.0,2.0,-2.0,2.0,-2.0,2.0); call should not be there. Move it to the initializer function and make sure the matrix mode is set to GL_PROJECTION.

rick_st3

Jun 24, 2008 at 5:12 AM

^^^^^

before or after glOrtho...??

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