Points jumping...
Author
Hey everyone!
I'm getting some weird results with very basic ogl code. It's all samples from "Beginning OpenGL GP" book.
I'm just testing the water, VERY basic stuff. Basically:
glBegin(GL_POINTS)
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(1.0, 0.0, 0.0);
glVertex3f(2.0, 0.0, 0.0);
glEnd();
This does what I expect, three points:
. . .
But when I do this, change a 'y' value:
glBegin(GL_POINTS)
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(1.0, 3.0, 0.0);
glVertex3f(2.0, 0.0, 0.0);
glEnd();
results: (Ignore the '-' I couldn't get the spacing to work so I just put those in to show what the points are doing.)
-.
. .
Something like that. For some reason, it jumps away from the previous 'x' spot (the middle). Shouldn't it be doing this:
--.
.--- .
As I said, I'm totally new to ogl, so I'm going over the code from the book like crazy (just chapter 3 so I might be missing something), looking for some state/setting that could be causing this.
Can anyone think of any? Or would it be better if I post the code?
Thanks a lot everyone!! Greatly appreciate it.
Just in case for those that have the book. I'm messing with the code from Chapter 3 pg. 46.
[Edited by - radioact1ve on November 27, 2005 1:42:02 AM]
Just a guess, but how have you setup your modelview and prjection matrices?
(e.g. ortho or frustum/perspective? Any glRotate/glTranslate?)
Although quite unlikely, you could get such results after a couple of transformations.
(e.g. ortho or frustum/perspective? Any glRotate/glTranslate?)
Although quite unlikely, you could get such results after a couple of transformations.
Author
Hey Seroja,
Thanks for the reply. In regard to those functions, this all I could find in the code. Of course I'm not really familiar with this, so I have no idea whats going on. 8)
Thanks for the reply. In regard to those functions, this all I could find in the code. Of course I'm not really familiar with this, so I have no idea whats going on. 8)
glMatrixMode(GL_PROJECTION); // set projection matrix current matrixglLoadIdentity(); // reset projection matrix// calculate aspect ratio of windowgluPerspective(52.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f);glMatrixMode(GL_MODELVIEW); // set modelview matrixglLoadIdentity();
So your code is:
It is strange that you see anything at all. Do you have any more setup code?
You draw the points at 0 Z. But your near plane is 1. You should not see anything. (Never tried points though, always used polygons)
How about trying to to make it a triangle?
I wonder whether you'll see your triangle at all.
If not, return to points, and add before the glBegin:
glTranslatef(0.0, 0.0, -5.0);
glMatrixMode(GL_PROJECTION); // set projection matrix current matrixglLoadIdentity(); // reset projection matrix// calculate aspect ratio of windowgluPerspective(52.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f);glMatrixMode(GL_MODELVIEW); // set modelview matrixglLoadIdentity();glBegin(GL_POINTS)glVertex3f(0.0, 0.0, 0.0);glVertex3f(1.0, 0.0, 0.0);glVertex3f(2.0, 0.0, 0.0);glEnd();// OrglBegin(GL_POINTS)glVertex3f(0.0, 0.0, 0.0);glVertex3f(1.0, 3.0, 0.0);glVertex3f(2.0, 0.0, 0.0);glEnd();It is strange that you see anything at all. Do you have any more setup code?
You draw the points at 0 Z. But your near plane is 1. You should not see anything. (Never tried points though, always used polygons)
How about trying to to make it a triangle?
glDisable(GL_LIGHTING); // No lightingglDisable(GL_CULL_FACE); // No face cullingglBegin(GL_TRIANGLES)glColor3f(1.0, 0.0, 0.0); // RedglVertex3f(0.0, 0.0, 0.0);glVertex3f(1.0, 3.0, 0.0);glVertex3f(2.0, 0.0, 0.0);glEnd();I wonder whether you'll see your triangle at all.
If not, return to points, and add before the glBegin:
glTranslatef(0.0, 0.0, -5.0);
Author
Oh no no... sorry! :) That's not how the code is.
And then a SetupProjection()
As for that triangle, I got a really small/weird red right triangle. But I did see something
Render() // My Render function{ float pointSize = 0.5; //float yPos = -15.0; // clear screen and depth buffer glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); gluLookAt(0.0, 6.0, 0.1, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); // draw a line of points of increasing size for (float point = -4.0; point < 5.0; point+=0.5) { // set the point size glPointSize(pointSize); // draw the point glBegin(GL_POINTS); //glVertex3f(point, 5.0, 0.0); glVertex3f(point, 0.0, 0.0); glEnd(); // increase the point size for the next point // yPos += 1.0; pointSize += 1.0; }}And then a SetupProjection()
SetupProjection(int width, int height){ if (height == 0) // don't want a divide by zero { height = 1; } // reset the viewport to new dimensions glViewport(0, 0, width, height); // set projection matrix current matrix glMatrixMode(GL_PROJECTION); glLoadIdentity(); // reset projection matrix // calculate aspect ratio of window gluPerspective(52.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f); glMatrixMode(GL_MODELVIEW); // set modelview matrix glLoadIdentity(); // reset modelview matrix m_windowWidth = width; m_windowHeight = height;}As for that triangle, I got a really small/weird red right triangle. But I did see something
Quote:Original post by radioact1ve
Oh no no... sorry! :) That's not how the code is.
*** Source Snippet Removed ***
And then a SetupProjection()
*** Source Snippet Removed ***
As for that triangle, I got a really small/weird red right triangle. But I did see something
Well now that you say you got gluLookAt it starts making sense.
I never used it so I can't tell you what to do, but experimenting a bit I think it is that call that is causing you the trouble. After transformations, seems like the Y axis that you are trying to change isn't Y axis anymore.
Try to remove that call, and instead translate back a bit to see what you're drawing.
You managed to get me confused about transformations for a whole 15 minutes :P
OK, so you are trying to render this:
-O-
O-O
Right?
Then don't do gluLookAt. Think of it as a drawing canvas. By calling gluLookAt you move the canvas. But instead of moving it away from you a bit just to see what is drawn, you also rotate it. Thus, Y axis as you think of it is now not really Y, but a different one. I don't want to get into gluLookAt to see exactly what transformations it does, but I'm 99% certain that you are drawing on a canvas that is not facing you (!) and thus get unusual results.
Use the following:
This will draw the points in diagonal-up. You can later change the code to draw only one of the points a bit above.
OK, so you are trying to render this:
-O-
O-O
Right?
Then don't do gluLookAt. Think of it as a drawing canvas. By calling gluLookAt you move the canvas. But instead of moving it away from you a bit just to see what is drawn, you also rotate it. Thus, Y axis as you think of it is now not really Y, but a different one. I don't want to get into gluLookAt to see exactly what transformations it does, but I'm 99% certain that you are drawing on a canvas that is not facing you (!) and thus get unusual results.
Use the following:
Render() // My Render function{ float pointSize = 0.5; //float yPos = -15.0; // clear screen and depth buffer glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); //gluLookAt(0.0, 6.0, 0.1, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); glTranslatef(0.0, 0.0, -6.0); // draw a line of points of increasing size for (float point = -4.0; point < 5.0; point+=0.5) { // set the point size glPointSize(pointSize); // draw the point glBegin(GL_POINTS); //glVertex3f(point, 5.0, 0.0); glVertex3f(point, point/2, 0.0); glEnd(); // increase the point size for the next point // yPos += 1.0; pointSize += 1.0; }}This will draw the points in diagonal-up. You can later change the code to draw only one of the points a bit above.
I would advise you to read up gluLookAt and understand it. However I think what you want is gluLookAt(0, 0, 6, 0, 0, 0, 0, 1, 0); This should give the same effect as glTranslatef(0, 0, -6).
Quote:Original post by CRACK123
I would advise you to read up gluLookAt and understand it. However I think what you want is gluLookAt(0, 0, 6, 0, 0, 0, 0, 1, 0); This should give the same effect as glTranslatef(0, 0, -6).
Were you talking to me, saying to read about gluLookAt? If so, I don't need it. I prefer Rotate & Translate, that way I'm sure what I'm doing.
And if I understand correctly, gluLookAt(0, 0, 6, 0, 0, 0, 0, 1, 0) will actually move the camera forward 6 and reverse it. glTranslatef(0, 0, -6) moves the camera backward.
I could be wrong, but I think the correct one would be gluLookAt(0, 0, -6, 0, 0, 0, 0, 1, 0). (Why not use Translate?)
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