How can I actually declare gluPerspective?
I mean I am drawing a spiral and I am setting z = -50 in the beginning and looping until the circle is complete. So what will be the declaration of gluPerspective?
Somewhere at the top of the source file you want to use gluPerspective in:
#include <GL/glu.h>
and then you can use gluPerspective with no problem.
I'm not really sure what you mean.gluPerspective() is typically used once when the program starts, then whenever the window is resized, to define the way primitives are projected to the screen.
You do that as so:
glMatrixMode(GL_PROJECTION); // Select The Projection Matrix
glLoadIdentity(); // Reset The Projection Matrix
gluPerspective(60,screenWidth/screenHeight,0.1,1000);
I strongly recommend that you have a look at the official OpenGL red book chapter 3, Viewing. There you'll find a good introduction to perspective projection.
Edit after comment:
Well if you would read the chapter carefully you would read this:
You can manufacture a viewing transformation in any of several ways, as described next. You can also choose to use the default location and orientation of the viewpoint, which is at the origin, looking down the negative z-axis.
and
void gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble near, GLdouble far);
Creates a matrix for a symmetric perspective-view frustum and multiplies the current matrix by it. fovy is the angle of the field of view in the x-z plane; its value must be in the range [0.0,180.0]. aspect is the aspect ratio of the frustum, its width divided by its height. near and far values the distances between the viewpoint and the clipping planes, along the negative z-axis. They should always be positive.
Related
I have the following problem, when I zoom in on the image. I have not been able to solve it. I am currently developing in Qt with c ++. I have a question about orthogonal projection and perspective projection. I need to zoom without traversing the image. I tried to make the glViewport bigger, but it does not work for me. The xmin, xmax... are the maximum and minimum values for each axis.
void MeshViewer::resizeGL(int width, int height)
{
int side = qMin(width, height);
if ( height == 0 )
height = 1;
glViewport(((GLint)(width - side)/2.0), (GLint)((height -side)/2.0), (GLint)side, (GLint)side);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glOrtho(xmin, xmax, ymin, ymax, zmin, zmax);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
glViewport specifies the mapping of normalized device coordinates to window coordinates (pixels).
If you want that the entire geometry which is inside the clip space, is mapped to the window, then it has to be:
glViewport(0, 0, width, height)
What the window displays is a frustum, defined by six planes. Normally, these planes are parallel, as in a cube. Anything that lies outside the frustum is not displayed.
"Zoom" may be interpreted, in a generic way, as "see bigger, nearer, more detail".
There are several ways of achieve the zoom effect:
Scale the objects. This works, the flaw is that objects (or parts of them) may lie before the near plane or behind the far plane of the frustum.
Move the camera towards the object. Same matter with near/far planes. Also, take care of moving through the model, you can set a "barrier" (perhaps a box) to prevent the camera moving too deep.
For an orthogonal projection, set left/right/top/bottom planes nearer to the object. This makes the frustum smaller, thus it's normal that some objects get clipped.
For a perspective projection you can do the same trick as with orthogonal. This trick is just to reduce the FOV (field of view) angle. If objects are too far, the perspective effect may be less obvious.
I have been trying to understand the the coordinates of the frustum gluPerspective() creates.
In case of glOrtho we explicitly define the coordinate space.
for example:
glOrtho(left, right,bottom,top,nearVal, farVal);
tells me what my x,y,z boundaries are, and I can conveniently place objects using
glVertex();
But in case of gluPerspective() I get the frustum but I don't know the the limits of x,y,z coordinates so sometimes when I draw the objects, it is not even in the view.
for example, if i define the frustum like
gluPerspective(45.0f, w/h, 0.1f, 100.0f);
and i draw something like :
glBegin(GL_POLYGON);
glVertex3f(30,30,50);
glVertex3f(-80,20,50);
glVertex3f(60,50,50);
glEnd();
where in the scene would it be? where is the origin located?
also, How the arguments of gluLookat() related to the arguments of gluPerspective();
gluLookat() transforms the objects from world coordinates to camera coordinates.
gluPerspective() Applies perspective to the objects.
The origin is (0,0,0). You locate it where your vertices say.
If you want to know the right and top parameters of the frustum use:
top = n * tan((fov*0.5f) * PI / 180.0f);
r = top * (float)w/(float)h;
In your case fov = 45.
gluLookat() and gluPerspective() have different purposes, so their arguments have nothing to do with each other.
You can use instead of gluPerspective():
glFrustum(left,right,bottom,top,nearVal,farVal)
Please see the following image:
Which mathematical method or POV-Ray/OpenGL command will lessen the convergence of a grid like this? (The grid converges too quickly; theta should be 90 degrees, matching the center line, for this purpose.)
Perspective is still desired, but convergence should happen at a slower rate, as if the distance was shorter or you were using a telephoto lens.
Although this image is from Blender, the methods being used are OpenGL and POV-Ray so a solution in either method would be appreciated.
I have some lines modeled in OpenGL and POV-Ray.
I have tried location, look--at, angle, right and up in POV-Ray, including camera transformations like rotate, scale, translate and matrix.
In OpenGL I have tried gluPerspective, glFrustum and glDepthRange.
Does anyone have a solution to this problem?
(Also, looking down on the grid is not an option in this case)
You're after an orthographic projection...
glOrtho()
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(left, right, bottom, top, near, far);
glMatrixMode(GL_MODELVIEW);
It's always nice to be able to swap between orthographic and perspective though since moving around a scene in orthographic can take a while to get used to.
There's an image here... https://blender.stackexchange.com/questions/648/what-are-the-differences-between-orthographic-and-perspective-views
edit
To keep using perspective, but with less perspective effect, you can decrease the field of view parameter. Unfortunately this will make the projection appear to zoom in. To undo the zoom, move the camera back. You can then update the near/far accordingly if need be.
Original Question/Code
I am fine tuning the rendering for a 3D object and attempting to implement a camera following the object using gluLookAt because the object's center y position constantly increases once it reaches it's maximum height. Below is the section of code where I setup the ModelView and Projection matrices:
float diam = std::max(_framesize, _maxNumRows);
float centerX = _framesize / 2.0f;
float centerY = _maxNumRows / 2.0f + _cameraOffset;
float centerZ = 0.0f;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(centerX - diam,
centerX + diam,
centerY - diam,
centerY + diam,
diam,
40 * diam);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0., 0., 2. * diam, centerX, centerY, centerZ, 0, 1.0, 0.0);
Currently the object displays very far away and appears to move further back into the screen (-z) and down (-y) until it eventually disappears.
What am I doing wrong? How can I get my surface to appear in the center of the screen, taking up the full view, and the camera moving with the object as it is updated?
Updated Code and Current Issue
This is my current code, which is now putting the object dead center and filling up my window.
float diam = std::max(_framesize, _maxNumRows);
float centerX = _framesize / 2.0f;
float centerY = _maxNumRows / 2.0f + _cameraOffset;
float centerZ = 0.0f;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(centerX - diam,
centerX,
centerY - diam,
centerY,
1.0,
1.0 + 4 * diam);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(centerX, _cameraOffset, diam, centerX, centerY, centerZ, 0, 1.0, 0.0);
I still have one problem when the object being viewed starts moving it does not stay perfectly centered. It appears to almost jitter up by a pixel and then down by 2 pixels when it updates. Eventually the object leaves the current view. How can I solve this jitter?
Your problem is with the understanding what the projection does. In your case glFrustum. I think the best way to explain glFrustum is by a picture (I just drew -- by hand). You start of a space called Eye Space. It's the space your vertices are in after they have been transformed by the modelview matrix. This space needs to be transformed to a space called Normalized Device Coordinates space. This happens in a two fold process:
The Eye Space is transformed to Clip Space by the projection (matrix)
The perspective divide {X,Y,Z} = {x,y,z}/w is applied, taking it into Normalized Device Coordinate space.
The visible effect of this is that of kind of a "lens" of OpenGL. In the below picture you can see a green highlighted area (technically it's a 3 volume) in eye space that, is the NDC space backprojected into it. In the upper case the effect of a symmetric frustum, i.e. left = -right, top = -bottom is shown. In the bottom picture an asymmetric frustum, i.e. left ≠ -right, top ≠ -bottom is shown.
Take note, that applying such an asymmetry (by your center offset) will not turn, i.e. rotate your frustum, but skew it. The "camera" however will stay at the origin, still pointing down the -Z axis. Of course the center of image projection will shift, but that's not what you want in your case.
Skewing the frustum like that has applications. Most importantly it's the correct method to implement the different views of left and right eye an a stereoscopic rendering setup.
The answer by Nicol Bolas pretty much tells what you're doing wrong so I'll skip that. You are looking for an solution rather than telling you what is wrong, so let's step right into it.
This is code I use for projection matrix:
glViewport(0, 0, mySize.x, mySize.y);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(fovy, (float)mySize.x/(float)mySize.y, nearPlane, farPlane);
Some words to describe it:
glViewport sets the size and position of display place for openGL inside window. Dunno why, I alsways include this for projection update. If you use it like me, where mySize is 2D vector specifying window dimensions, openGL render region will ocuppy whole window. You should be familiar with 2 next calls and finaly that gluPerspective. First parameter is your "field of view on Y axis". It specifies the angle in degrees how much you will see and I never used anything else than 45. It can be used for zooming though, but I prefer to leave that to camera operating. Second parameter is aspect. It handles that if you render square and your window sizes aren't in 1:1 ratio, it will be still square. Third is near clipping plane, geometry closer than this to camera won't get rendered, same with farPlane but on contrary it sets maximum distance in what geometry gets rendered.
This is code for modelview matrix
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt( camera.GetEye().x,camera.GetEye().y,camera.GetEye().z,
camera.GetLookAt().x,camera.GetLookAt().y,camera.GetLookAt().z,
camera.GetUp().x,camera.GetUp().y,camera.GetUp().z);
And again something you should know: Again, you can use first 2 calls so we skip to gluLookAt. I have camera class that handles all the movement, rotations, things like that. Eye, LookAt and Up are 3D vectors and these 3 are really everything that camera is specified by. Eye is the position of camera, where in space it is. LookAt is the position of object you're looking at or better the point in 3D space at which you're looking because it can be really anywhere not just center object. And if you are worried about what's Up vector, it's really simple. It's vector perpedicular to vector(LookAt-Eye), but becuase there's infinite number of such vectors, you must specify one. If your camera is at (0,0,0) and you are looking at (0,0,-1) and you want to be standing on your legs, up vector will be (0,1,0). If you'd like to stand on your head instead, use (0,-1,0). If you don't get the idea, just write in comment.
As you don't have any camera class, you need to store these 3 vectors separately by yourself. I believe you have something like center of 3D object you're moving. Set that position as LookAt after every update. Also in initialization stage(when you're making the 3D object) choose position of camera and up vector. After every update to object position, update the camera position the same way. If you move your object 1 point up at Y axis, do the same to camera position. The up vectors remains constant if you don't want to rotate camera. And after every such update, call gluLookAt with updated vectors.
For updated post:
I don't really get what's happening without bigger frame of reference (but I don't want to know it anyway). There are few things I get curious about. If center is 3D vector that stores your object position, why are you setting the center of this object to be in right top corner of your window? If it's center, you should have those +diam also in 2nd and 4th parameter of glOrtho, and if things get bad by doing this, you are using wrong names for variables or doing something somewhere before this wrong. You're setting the LookAt position right in your updated post, but I don't find why you are using those parameters for Eye. You should have something more like: centerX, centerY, centerZ-diam as first 3 parameters in gluLookAt. That gives you the camera on the same X and Y position as your object, but you will be looking on it along Z axis from distance diam
The perspective projection matrix generated by glFrustum defines a camera space (the space of vertices that it takes as input) with the camera at the origin. You are trying to create a perspective matrix with a camera that is not at the origin. glFrustum can't do that, so the way you're attempting to do it simply will not work.
There are ways to generate a perspective matrix where the camera is not at the origin. But there's really no point in doing that.
The way a moving camera is generally handled is by simply adding a transform from the world space to the camera space of the perspective projection. This just rotates and translates the world to be relative to the camera. That's the job of gluLookAt. But your parameters to that are wrong too.
The first three values are the world space location of the camera. The next three should be the world-space location that the camera should look at (the position of your object).
I'm planning to create a tiled world with OpenGL, with slightly rotated tiles and houses and building in the world will be made of models.
Can anybody suggest me what projection(Orthogonal, Perspective) should I use, and how to setup the View matrix(using OpenGL)?
If you can't figure what style of world I'm planning to create, look at this game:
http://www.youtube.com/watch?v=i6eYtLjFu-Y&feature=PlayList&p=00E63EDCF757EADF&index=2
Using Orhtogonal vs Perspective projection is entirely an art style choice. The Pokemon serious you're talking about is orthogonal -- in fact, it's entirely layered 2D sprites (no 3D involved).
OpenGL has no VIEW matrix. It has a MODELVIEW matrix and a PROJECTION matrix. For Pokemon-style levels, I suggest using simple glOrtho for the projection.
Let's assume your world is in XY space (coordinates for tiles, cameras, and other objects are of the form [x, y, 0]). If a single tile is sized 1,1, then something like glOrtho(12, 9, -10, 10) would be a good projection matrix (12 wide, 9 tall, and Z=0 is the ground plane).
For MODELVIEW, you can start by loading identity, glTranslate() by the tile position, and then glTranslate() by the negative of the camera position, before you draw your geometry. If you want to be able to rotate the camera, you glRotate() by the negative (inverse) of the camera rotation between the two Translate()s. In the end, you end up with the following matrix chain:
output = Projection × (CameraTranslation-1 × CameraRotation-1 × ModelLocation × ModelRotation) × input
The parts in parens are MODELVIEW, and the "-1" means "inverse" which really is negative for translation and transpose for rotation.
If you want to rotate your models, too, you generally do that first of all (before the first glTranslate().
Finally, I suggest the OpenGL forums (www.opengl.org) or the OpenGL subforums of www.gamedev.net might be a better place to ask this question :-)
The projection used by that video game looks Oblique to me. There are many different projections, not just perspective and orthographic. See here for a list of the most common ones: http://en.wikipedia.org/wiki/File:Graphical_projection_comparison.png
You definitely want perspective, with a fixed rotation around the X-axis only. Around 45-60 degrees or thereof. If you don't care about setting up the projection code yourself, the gluPerspective function from the GLU library is handy.
Assuming OpenGL 2.1:
glMatrixMode(GL_PROJECTION); //clip matrix
glLoadIdentity();
gluPerspective(90.0, width/height, 1.0, 20.0);
glMatrixMode(GL_MODELVIEW); //world/object matrix
glLoadIdentity();
glRotatef(45.0f, 1.0f, 0.0f, 0.0f);
/* render */
The last two parameters to gluPerspective is the distance to the near and far clipping planes. Their values depend on the scale you use for the environment.