I have a simple program to use depth test. It is not working as expected. The program draws X, Y axis and a sphere near the origin.
If I don't turn on the GL_DEPTH_TEST, the sphere is drawn over the axis. If I turn on the GL_DEPTH_TEST, the axis are drawn over the sphere which I was not expecting. Can someone tell me what I did
wrong ?
void
glwid::initializeGL()
{
glClearColor (0.0f, 0.0f, 0.0f, 1.0f);
}
void
glwid::resizeGL(int width, int height)
{
glViewport( 0, 0, (GLint)width, (GLint)height );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective ( 90, (GLint)width/ (GLint)height, 0.0, 200.0 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glEnable (GL_DEPTH_TEST);
}
void
glwid::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
gluLookAt (0, 0, 100, 0, 0, 0, 0, 1, 0);
//
// X axis
//
glBegin( GL_LINES );
qglColor( green );
glVertex3f (-100.0, 0, 0. );
glVertex3f (100.0, 0, 0. );
glEnd();
//
// Y axis
//
glBegin( GL_LINES );
qglColor( red );
glVertex3f (0.0, 100.0, 0. );
glVertex3f (0.0, -100, 0. );
glEnd();
//
// sun
//
glTranslated (5, 0, 20);
GLUquadricObj *sphere_quadric = gluNewQuadric();
glColor3ub (255, 255, 0);
gluQuadricDrawStyle(sphere_quadric, (GLenum)GLU_SMOOTH);
gluSphere(sphere_quadric, 10, 36, 36);
}
I've tried your code. The problem is in resizeGL() function.
The problem was your putting to
gluPerspective ( 90, (GLint)width/ (GLint)height, 0.0, 200.0 );
0.0 value as a third argument. Put 0.01 for example - and everything will be ok. that's because this parameter should always be positive:
http://www.opengl.org/sdk/docs/man/xhtml/gluPerspective.xml
Also change (GLint)width/ (GLint)height to (GLfloat)width/ (GLfloat)height otherwise the result will be strange.
And it's better to put glEnable(GL_DEPTH_TEST) into initializeGL() function
Your axis starts at Z location 0. The Sphere is at Z location 20 (farther away from the "camera") therefore the axis is in-front of the sphere and is being shown.
As you currently have it setup, as Z values go up they move away from the screen. As they go down, they are going closer to the screen.
You have two options: Disable depth testing while drawing your axis (therefore it will always be behind everything). Or move your axis to Z position 100 or so and scale it up to make it look the same size. Option one is probably better.
Simply wrapping your axis drawing routines in glDisable(GL_DEPTH_TEST); and glEnable (GL_DEPTH_TEST); should do the trick
Related
I draw many lines to form a grid. I want to see the grid rotated on its X-axis, but I never get the intended result. I tried glRotatef and gluLookAt which does not work the way I want. Please see the pictures below.
this is the grid
this is how I want to see it
Edit: geez, posting the code here is also hard, lol, anyway here it is.
Edit2: removed, only leave the code that has issues.
Please find the code below, no matter how I set the gluLookAt, the grid result won't be in the perspective I want.
#include <GL/glut.h>
void display() {
...
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_LINES);
for (int i = 0; i < 720; i += 3)
{
glColor3f(0, 1, 1);
glVertex3f(linePoints[i], linePoints[i + 1], linePoints[i + 2]);
}
glEnd();
glFlush();
}
void init() {
glClearColor(0.0, 0.0, 0.0, 1.0);
glColor3f(1.0, 1.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, 4.0 / 3.0, 1, 40);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, -2, 1.25, 0, 0, 0, 0, 1, 0);
}
Lets assume, that you have a grid in the xy plane of the world:
glColor3f(0, 1, 1);
glBegin(GL_LINES);
for (int i = 0; i <= 10; i ++)
{
// horizontal
glVertex3f(-50.0f + i*10.0f, -50.0f, 0.0f);
glVertex3f(-50.0f + i*10.0f, 50.0f, 0.0f);
// vertical
glVertex3f(-50.0f, -50.0f + i*10.0f, 0.0f);
glVertex3f( 50.0f, -50.0f + i*10.0f, 0.0f);
}
glEnd();
Ensure that the distance of to the far plane of the projection is large enough (see gluPerspective). All the geometry which is not in between the near an far plane of the Viewing frustum is clipped.
Further more ensure that the aspect ratio (4.0 / 3.0) match the ratio of the viewport rectangle (window).
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, 4.0 / 3.0, 1, 200);
For the use of gluLookAt, the up vector of the view has to be perpendicular to the grid. If the grid is arranged parallel to the xy plane, then the up vector is z axis (0, 0, 1).
The target (center) is the center of the grid (0, 0, 0).
The point of view (eye position) is ought to be above and in front of the grid, for instance (0, -55, 50). Note the point of view is used for a grid with the bottom left of (-50, -50, 0) and a top right of (50, 50, 0).
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, -55.0, 50.0, 0, 0, 0, 0, 0, 1);
I am a beginner in OpenGl and I am struggling a bit with setting up the glOrtho camera to match the window size so that I can draw a line using the window's coordinates. For example, if I want to draw a line from coordinates 0,10 (x,y) to 600,10. I managed to draw the line (which will be a "Separator" from the viewport and a toolbar with buttons) in my current set up but it was by "try end error" approach and the coordinates that I needed to put don't make any sense to me. When I tried to draw a line using the above-mentioned coordinates, the line simply did not show up. What I need to change in the glOrtho set up in order to work with these (1000x600) screen size and draw my vertices and not these:
glVertex3f(-2.0, 11.0, 0.0);
glVertex3f(20.0, 11.0, 0.0);
Note, my current window size is 1000x600 (width/height)
This is the line (on the top that crosses the whole screen):
This is my OGWindow class that handles all of the drawing:
void OGWindow::MyReSizeGLScene(int fwidth, int fheight)
{
// Store window size in class variables so it can be accessed in myDrawGLScene() if necessary
wWidth = fwidth;
wHeight = fheight;
// Calculate aspect ration of the OpenGL window
aspect_ratio = (float) fwidth / fheight;
// Set camera so it can see a square area of space running from 0 to 10
// in both X and Y directions, plus a bit of space around it.
Ymin = -1;
Ymax = 12;
Xmin = -1;
// Choose Xmax so that the aspect ration of the projection
// = the aspect ratio of the viewport
Xmax = (aspect_ratio * (Ymax -Ymin)) + Xmin;
glMatrixMode(GL_PROJECTION); // Select The Projection Stack
glLoadIdentity();
glOrtho(Xmin, Xmax, Ymin, Ymax, -1.0, 1.0);
glViewport(0, 0, wWidth, wHeight); // Viewport fills the window
}
void OGWindow::myDrawGLScene(GLvoid) // Here's Where We Do All The Drawing
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear the drawing area
OGWindow::myDrawModel();
drawToolbar();
glutSwapBuffers(); // Needed if we're running an animation
glFlush();
}
void OGWindow::myDrawModel(GLvoid)
{
switch ( squareColour ) {
case RED:
glColor3f(1.0, 0.0, 0.0);
break;
case BLUE:
glColor3f(0.0, 0.0, 1.0);
break;
}
glBegin( GL_QUADS );
glVertex3f( squareX, squareY, 0.0 ); // Coordinates of bottom-left corner of square
glVertex3f( squareX + squareWidth, squareY, 0.0 );
glVertex3f( squareX + squareWidth, squareY + squareHeight, 0.0 );
glVertex3f( squareX, squareY + squareHeight, 0.0 );
glEnd();
}
// Convert from screen coords returned by mouse
// to world coordinates.
// Return result in worldX, worldY
void OGWindow::screen2World(int screenX, int screenY, double & worldX, double & worldY)
{
// Dimensions of rectangle viewed by camera projection
double projWidth = Xmax -Xmin;
double projHeight = Ymax - Ymin;
// Screen coords with origin at bottom left
int screenLeft = screenX;
int screenUp = wHeight - screenY;
worldX = Xmin + screenLeft * projWidth / wWidth ;
worldY = Ymin + screenUp * projHeight / wHeight ;
}
//Method to draw the toolbar separator line
void OGWindow::drawToolbar(GLvoid) {
//draw toolbar line separator
glColor3f(0.0,0.0,0.0);
glBegin(GL_LINES);
glVertex3f(-2.0, 11.0, 0.0);
glVertex3f(20.0, 11.0, 0.0);
glEnd();
//draw create button
glPushMatrix();
glTranslatef(2.0, 10.0, 0.0);
glutSolidCube(2.0);
glPopMatrix();
}
This is my main class where I am ivoking the methods from OGWindow:
int main(int argc, char **argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowSize( 1000, 600 );
glutInitWindowPosition(0, 0);
glutCreateWindow("OpenGL Demo");
glEnable(GL_DEPTH_TEST); // enable the depth buffer test
glutDisplayFunc(DrawGLScene);
glutReshapeFunc(ReSizeGLScene);
glutMouseFunc(mouseClick);
glutMotionFunc(mouseMotion);
glutPassiveMotionFunc(mousePassiveMotion);
glutIdleFunc(Idle);
theWindow.initGL();
glutMainLoop();
}
Check out the documentation of glOrtho function. As you see, there are 6 parameters: left, right, bottom, top, near, far. You made mistake by setting window width to top instead of bottom parameter. Here's proper use of function:
glOrtho (0, 1000, 600, 0, -1.0, 1.0)
So, first your ortho settings. If you want your camera to match the screen dimensions, glOrtho has to use the same dimensions.
// This will anchor the camera to the center of the screen
// Camera will be centered on (0,0)
glOrtho( -screenWidth/2.f, screenWidth/2.f, -screenHeight/2.f, screenHeight/2.f, -1, 1 );
// This will anchor the camera to the lower left corner of the screen
// Camera will be centered on (screenWidth/2, screenHeight/2)
glOrtho( 0, screenWidth, 0, screenHeight, -1, 1 );
Try both and see the difference. Although if you are making some sort of editor, where your camera doesn't move, you may be looking for the second ortho setup.
Second, you only ever use (apparently) the GL_PROJECTION matrix mode. You must use this mode to set the camera projection and GL_MODELVIEW to apply transforms to the camera or the objects.
So when you call resize and don't change the matrix mode back to GL_MODELVIEW, you'll be applying translations to the projection matrix.
If you did forget to initialize the modelview matrix it may contain garbage values and yield unexpected results.
In OpenGL's fixed pipeline, by default, specifying vertex coordinates using glVertex3f is equivalent to specifying a location between -1.0 and +1.0 in screen space. Therefore, given a set of 4 perfectly adjacent screen-space vertices using GL_TRIANGLE_STRIP (or even GL_QUADS), and unless your window is already perfectly square, you will always render a rectangle instead of a perfect square...
Knowing the width, height and aspect ratio of a window, is there some way to correct this?
I have tried multiplying the vertex coordinates by the aspect ratio, which unfortunately seemed to achieve the same visual effect.
Here's the full source code I'm currently using:
#include "main.h"
#pragma comment(lib, "glut32.lib")
int g_width = 800;
int g_height = 600;
int g_aspectRatio = double(g_width) / double(g_height);
bool g_bInitialized = false;
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(0, 0);
glutInitWindowSize(g_width, g_height);
glutCreateWindow("OpenGL Test App");
glutDisplayFunc(onRender);
glutReshapeFunc(onSize);
glutIdleFunc(onRender);
glutMainLoop();
return 0;
}
void onInit()
{
glFrontFace(GL_CW);
}
void onRender()
{
if(!g_bInitialized)
onInit();
static float angle = 0.0f;
const float p = 0.5f * g_aspectRatio;
glLoadIdentity();
gluLookAt(
0.0f, 0.0f, 10.0f,
0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f
);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glScalef(1, -1, 1); // Flip the Y-axis
glRotatef(angle, 0.0f, 1.0f, 0.0f);
glBegin(GL_TRIANGLE_STRIP);
{
glColor4f(1.0, 0.0, 0.0, 1.0); // Red
glVertex3f(-p, -p, 0.0); // Top-Left
glColor4f(0.0, 1.0, 0.0, 1.0); // Green
glVertex3f(p, -p, 0.0); // Top-Right
glColor4f(0.0, 0.0, 1.0, 1.0); // Blue
glVertex3f(-p, p, 0.0); // Bottom-Left
glColor4f(1.0, 1.0, 0.0, 1.0); // Yellow
glVertex3f(p, p, 0.0); // Bottom-Left
}
glEnd();
angle += 0.6f;
glutSwapBuffers();
}
void onSize(int w, int h)
{
g_width = max(w, 1);
g_height = max(h, 1);
g_aspectRatio = double(g_width) / double(g_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, w, h);
gluPerspective(45, g_aspectRatio, 1, 1000);
glMatrixMode(GL_MODELVIEW);
}
EDIT:
This has been solved... In the above code, I had defined g_aspectRatio as an int instead of a floating-point value. Therefore, it's value was always 1...
In my (old) experience, that's just why you have an aspect ratio argument to gluPerspective().
The manual page says:
In general, the aspect ratio in gluPerspective should match
the aspect ratio of the associated viewport. For example, aspect = 2.0
means the viewer's angle of view is twice as wide in x as it is in y.
If the viewport is twice as wide as it is tall, it displays the image
without distortion.
Check your g_aspectRatio value.
by default, specifying vertex coordinates using glVertex3f is equivalent to specifying a location between -1.0 and +1.0 in screen space
Wrong. Coordinates passed to OpenGL through glVertex or a glVertexPointer vertex array are in model space. The transformation to screen space happens by transforming into view space by the modelview matrix and from view space to clip space by the projection matrix. Then clipping is applied and the perspective divide applied to reach normalized coordinate space.
Hence the value range for glVertex can be whatever you like it to be. By applying the right projection matrix you get your view space to be in [-aspect; aspect]×[-1, 1] if you like that.
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-aspect, aspect, -1, 1, -1, 1);
I'm going to show FPS on the screen with the freeglut function glutBitmapString,but it shows nothing. Here is my code. Is there anyone can figure where the problem is?
void PrintFPS()
{
frame++;
time=glutGet(GLUT_ELAPSED_TIME);
if (time - timebase > 100) {
cout << "FPS:\t"<<frame*1000.0/(time-timebase)<<endl;
char* out = new char[30];
sprintf(out,"FPS:%4.2f",frame*1000.0f/(time-timebase));
glColor3f(1.0f,1.0f,1.0f);
glRasterPos2f(20,20);
glutBitmapString(GLUT_BITMAP_TIMES_ROMAN_24,(unsigned char* )out);
timebase = time;
frame = 0;
}
}
void RenderScene(void)
{
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
GLfloat vRed[] = { 1.0f, 0.0f, 0.0f, 0.5f };
GLfloat vYellow[] = {1.0f,1.0f,0.0f,1.0f};
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vYellow);
//triangleBatch.Draw();
squareBatch.Draw();
PrintFPS();
glutSwapBuffers();
}
it supposed to show the FPS on the top left of the screen
The position that's provided by glRasterPos is treated just like a vertex, and transformed by the current model-view and projection matrices. In you example, you specify the text to be position at (20,20), which I'm guessing is supposed to be screen (viewport, really) coordinates.
If it's the case that you're rendering 3D geometry, particularly with a perspective projection, your text may be clipped out. However, there are (at least) two simple solutions (presented in order of code simplicity):
use one of the glWindowPos functions instead of glRasterPos. This function bypasses the model-view and projection transformations.
use glMatrixMode, glPushMatrix, and glPopMatrix to temporarily switch to window coordinates for rendering:
// Switch to window coordinates to render
glMatrixMode( GL_MODELVIEW );
glPushMatrix();
glLoadIdentity();
glMatrixMode( GL_PROJECTION );
glPushMatrix();
glLoadIdentity();
gluOrtho2D( 0, windowWidth, 0, windowHeight );
glRasterPos2i( 20, 20 ); // or wherever in window coordinates
glutBitmapString( ... );
glPopMatrix();
glMatrixMode( GL_MODELVIEW );
glPopMatrix();
I have a simple rectangle i have drawn on screen in opengl.
My target is to draw this rectangle in 3D so the left side of it is deeper (z-axis) than the right side.
Look at this pic so you can see what i mean:
http://www.battleteam.net/tech/fis/docs/images/metroid_hud1.png
This is the code i use to draw a rectangle which uses different colors and i moved both points on left side up a bit.
glColor4f( 1.0, 1.0, 1.0, 1.0 );
glVertex3f( 0, -20, z_left );
glColor4f( 0.0, 1.0, 1.0, 1.0 );
glVertex3f( SQUARE_WIDTH, 0, 0 );
glColor4f( 1.0, 0.0, 1.0, 1.0 );
glVertex3f( SQUARE_WIDTH, SQUARE_HEIGHT, 0 );
glColor4f( 1.0, 1.0, 0.0, 1.0 );
glVertex3f( 0, SQUARE_HEIGHT-20, z_left );
I use the z_left variable to dynamically change the z-value for the both points on the left side to move these points on the z-axis. But what happens is that the rectangle gets cut off from the left side. This happens when the z_left value reaches the zFar or zNear Variable defined via the "glOrtho" function call.
My glOrtho looks like this:
glOrtho( 0, SCREEN_WIDTH, SCREEN_HEIGHT, 0, -100, 100 );
So if the z_left gets higher than 100 or less than -100 then that strange cutting off begins. I dont know why. I expected to get the left side of the rectangle to be moved on z-axis, means moving it deeper (away from eye) or closer.
Can somebody tell me whats wrong here? The rest of the code is pretty simple and standard.
A simple rectangle in a 3D environment being changed a bit to have a "3d panel" like rectangle.
My OpenGL init looks like this.
glClearColor( 0, 0, 0, 0 );
glMatrixMode( GL_PROJECTION );
glLoadIdentity(); glOrtho( 0, SCREEN_WIDTH, SCREEN_HEIGHT, 0, -100, 100 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
Thanks for any help.
Ortographic projections have that property, you can move them in the Z axis, but the object looks the same. Switch to a perspective projection, on which objects get smaller with distance to the camera.
About the culling, you're drawing outside the viewing cube (when Z < -100 or Z > 100). The projection will cull away anything outside it's view.