OpenGl rotation/translation problems?

wyrmmage

Moderator

Posts: 370
Joined: 2006.08

Post: #1

Jan 5, 2008 — 10:26 PM

I've been having some problems with OpenGl not displaying textured objects the way I want it to

Everything I'm doing is composed of texture-mapped quads that have straight sides, but for some reason when they're rendered the side are not perfectly straight. From what I can tell, these imperfections are always one pixel in difference from what they're supposed to be.
Here's a link to the app: http://www.wyrmmage.com/client.zip and its contents in zipped form. (if you download the app, you can press 'e' in the menu and right-click to resize the elements; press 'e' again to stop resizing). Click on multiplayer, then the top text to be taken to the cube/plane test...use w and s to zoom out/mouse to rotate (rotation is backward, sorry).
I've also taken some screenshots in case you don't download the app.
The below one is my main menu:
[Image: menu_small.png]

and another one with the object a bit larger (notice the top of the object is larger than the bottom for some reason)
[Image: menu_big.png]

then here's one of the cube and the plane; the plan should be parallell to the cube, but instead it's titled.
[Image: cube_plane.png]

here's the code for for drawing the menu:

Code:

glTranslated(theCamera.x, theCamera.y, theCamera.z);

glRotatef(theCamera.rotX, 1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, 1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, 1.0);

(this->*funcDraw)(theNewTime);

glRotatef(theCamera.rotX, -1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, -1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, -1.0);

glTranslated(-1*theCamera.x, -1*theCamera.y, -1*theCamera.z);

(this->*funcDraw)(theNewTime) draws a rectangle with points:
-0.925 0.275 0
0.645 0.275 0
0.645 0.565 0
-0.925 0.565 0
and texture coords
0 0
1 0
1 1
0 1
the camera x,y and rotX, rotY, rotZ are all 0, and camera z is set to 6 so that I can see my objects I'm drawing.

Then for the cube/plane I have the same code as above, but (this->*funcDraw)(theNewTime) draws the cube and then the plane, with points
-8 -8 8
8 -8 8
8 -8 -8
-8 -8 -8
and texture coords
0 0
1 0
1 1
0 1

also, here's my code to set up openGl:

Code:

glShadeModel(GL_SMOOTH);                            // Enable Smooth Shading

glEnable(GL_TEXTURE_2D);

glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);

glEnable(GL_BLEND);        // Turn Blending On

glClearColor(0.0f, 0.0f, 0.0f, 0.5f);                // Black Background

glClearDepth(1.0f);                                    // Depth Buffer Setup

glEnable(GL_DEPTH_TEST);                            // Enables Depth Testing

glDepthFunc(GL_LEQUAL);                                // The Type Of Depth Testing To Do

glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);    // Really Nice Perspective Calculations

and when the window is resized:

Code:

width,height);                        // Reset The Current Viewport

windowX = (double)width;

windowY = (double)height;

glMatrixMode(GL_PROJECTION);                        // Select The Projection Matrix

glLoadIdentity();                                    // Reset The Projection Matrix

// Calculate The Aspect Ratio Of The Window

gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);

glMatrixMode(GL_MODELVIEW);                            // Select The Modelview Matrix

glLoadIdentity();                                    // Reset The Modelview Matrix

Sorry for such a long post...I figured too much information was better than too little XD
Thanks in advance

-wyrmmage

Worlds at War (Current Project) - http://www.awkward-games.com/forum/

sohta

Member

Posts: 72
Joined: 2006.10

Post: #2

Jan 6, 2008 — 02:25 AM

Code:

glTranslated(theCamera.x, theCamera.y, theCamera.z);

glRotatef(theCamera.rotX, 1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, 1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, 1.0);

(this->*funcDraw)(theNewTime);

glRotatef(theCamera.rotX, -1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, -1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, -1.0);

glTranslated(-1*theCamera.x, -1*theCamera.y, -1*theCamera.z);

Assuming that you want to do the following:
- Apply tranform
- Render
- Nullify transform

Then you should apply all transforms in reverse order when canceling the transform. Your block of code should read:

Code:

glTranslated(theCamera.x, theCamera.y, theCamera.z);

glRotatef(theCamera.rotX, 1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, 1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, 1.0);

(this->*funcDraw)(theNewTime);

glRotatef(theCamera.rotZ, 0.0, 0.0, -1.0);

glRotatef(theCamera.rotY, 0.0, -1.0, 0.0);

glRotatef(theCamera.rotX, -1.0, 0.0, 0.0);

glTranslated(-1*theCamera.x, -1*theCamera.y, -1*theCamera.z);

or even better:

Code:

glPushMatrix();

glTranslated(theCamera.x, theCamera.y, theCamera.z);

glRotatef(theCamera.rotX, 1.0, 0.0, 0.0);

glRotatef(theCamera.rotY, 0.0, 1.0, 0.0);

glRotatef(theCamera.rotZ, 0.0, 0.0, 1.0);

(this->*funcDraw)(theNewTime);

glPopMatrix();

I am willing to bet that this is what is causing your issues

wyrmmage

Moderator

Posts: 370
Joined: 2006.08

Post: #3

Jan 6, 2008 — 01:58 PM

Thank you so much! ^_^
That was my problem

Worlds at War (Current Project) - http://www.awkward-games.com/forum/

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