I have simple studyng project representing some space star's system. I have a star and several planets with moons rotating around the star. I'm using depth buffer, but planets are always in front of the star even if planet should be shadowed by the star. What can be the issue reason?
void drawPlanet(float orbitRadius, float planetRadius, float daysInYear, float hoursInDay){
static float year = 0;
static float days = 0;
static float hours = 0;
glPushMatrix();
glRotatef(year, 0, 1, 0);
glTranslatef(orbitRadius, 0 ,0);
glRotatef(days, 1, 2, 0);
glutWireSphere(planetRadius, 20, 16);
drawLuna(0.3, 0.1, 30, 15);
glPopMatrix();
hours++;
days = hours/hoursInDay;
year=days/daysInYear;
}
void display(void){
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
gluLookAt(0,0,5, 0, 0, 0, 0 ,1, 0);
glColor3f(1.0, 0.647059, 0.00);
glutSolidSphere(0.5, 20, 16);
glColor3b(197, 96, 63);
drawPlanet(2, 0.2, 50, 12);
drawPlanet(1, 0.15, 30, 15);
glFlush();
}
int main(int argc, char** argv)
{
....
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glEnable(GL_DEPTH_TEST);
....
}
Your call to glEnable(GL_DEPTH_TEST) has no effect if there's no OpenGL context. GLUT creates the OpenGL context only after glutCreateWindow has been called.
As a general rule you should not call glEnable outside of the display function. You will also have to clear the depth buffer, so make this
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
Related
I drew a rectangle in the X-Z play of a 3D, XYZ, plane using the code below.
#include <GL/glut.h>
void drawPlane() {
GLfloat A[3] = { 0, 0, 0};
GLfloat B[3] = { 1, 0, 0};
GLfloat C[3] = { 1, 0, 1};
GLfloat D[3] = { 0, 0, 1};
glBegin(GL_POLYGON);
glVertex3fv(A);
glVertex3fv(B);
glVertex3fv(C);
glVertex3fv(D);
glEnd();
}
// Display Call Back
void draw(){
glLoadIdentity();
glTranslatef(0.0, 0.5, 1); //i thought this would do the camera thing
drawPlane();
glutSwapBuffers();// Render Now
return;
}
// Initialization
void initialize()
{
glClearColor(0.1f, 0.1f, 0.1f, 0.1f); // Set Background Color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear all drawings in buffer
}
// Main
int main(int argc, char* argv[])
{
glutInit(&argc, argv); // Initialize GLUT
int x = 512, y = 512; // x and y value
glutInitWindowPosition(
(int)(glutGet(GLUT_SCREEN_WIDTH) - x) / 2,
(int)(glutGet(GLUT_SCREEN_HEIGHT) - y) / 2); // Position the window's center
glutInitWindowSize(x, y); // Set the window's initial width & height
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); // ESSENTIAL BUT HAVE NO IDEA WHAT THIS DOES
glutCreateWindow("3d Bowling Game"); // Create a window with the given title
glutDisplayFunc(draw); // Register display callback handler for window re-paint
glutMainLoop(); // Enter the event-processing loop
initialize();
return 0;
}
How do I change the camera angle in order to view all of the coordinates like below.
I'm trying to look at the square from the other side using the gluLookAt() function.
After using the function, nothing changes, although I expected that the corners of the square will change.
I set the camera point to the rightmost part of the world and look at its center, where the square is located.
He had to stretch out to the sides. Why hasn't anything changed?
Code:
#include "includes.h"
using namespace std;
constexpr auto FPS_RATE = 60;
int windowHeight = 600, windowWidth = 600, windowDepth = 600;
void init();
void idleFunction();
void displayFunction();
double getTime();
double getTime()
{
using Duration = std::chrono::duration<double>;
return std::chrono::duration_cast<Duration>(
std::chrono::high_resolution_clock::now().time_since_epoch()
).count();
}
const double frame_delay = 1.0 / FPS_RATE;
double last_render = 0;
void init()
{
glutDisplayFunc(displayFunction);
glutIdleFunc(idleFunction);
glViewport(0, 0, windowWidth, windowHeight);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-windowWidth / 2, windowWidth / 2, -windowHeight / 2, windowHeight / 2, -windowDepth / 2, windowDepth / 2);
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
}
void idleFunction()
{
const double current_time = getTime();
if ((current_time - last_render) > frame_delay)
{
last_render = current_time;
glutPostRedisplay();
}
}
void displayFunction()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBegin(GL_POLYGON);
gluLookAt(-300, 0, 0,
0, 0, 0,
0, 1, 0);
glColor3f(1, 1, 1);
glVertex3i(-150, 150, 0);
glVertex3i(150, 150, 0);
glVertex3i(150, -150, 0);
glVertex3i(-150, -150, 0);
glEnd();
glutSwapBuffers();
}
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(windowWidth, windowHeight);
glutInitWindowPosition((GetSystemMetrics(SM_CXSCREEN) - windowWidth) / 2, (GetSystemMetrics(SM_CYSCREEN) - windowHeight) / 2);
glutCreateWindow("Window");
init();
glutMainLoop();
return 0;
}
The issue is caused because gluLookAt() is call with in a glBegin/glEnd sequence. This is not allowed. You've to call gluLookAt before glBegin.
Once drawing of primitives was started by glBegin it is only allowed to specify vertex coordinates (glVertex) and change attributes (e.g. glColor, glTexCoord ...), till the drawn is ended (glEnd).
All other instruction will be ignored and cause a GL_INVALID_OPERATION error (error code 1282).
Further note, that glLookAt doesn't set a the current matrix. It defines a matrix and multiplies the current matrix by the new matrix. Set the matrix mode (glMatrixMode) and set Identity matrix by glLoadIdentity before gluLookAt.
With the view matrix
gluLookAt(-300, 0, 0, 0, 0, 0, 0, 1, 0);
you want "see" anything, because with that matrix the line of sight is set along the x-axis and you look at the 2 dimensional polygon from the side.
Note, the polygon is a 2D object. The size of the object appears different if you look at it from the front, from the side (then it is a line and not visible) or from an direction in between. The first 3 parameters of gluLookAt define the point of view the next 3 parameters define the point you look at. The vector from the point of view to the point you look at is the line of sight.
Probably yo want look along the z-axis:
void displayFunction()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, 0, -300, 0, 0, 0, 0, 1, 0);
glBegin(GL_POLYGON);
glColor3f(1, 1, 1);
glVertex3i(-150, 150, 0);
glVertex3i(150, 150, 0);
glVertex3i(150, -150, 0);
glVertex3i(-150, -150, 0);
glEnd();
glutSwapBuffers();
}
You use Orthographic (parallel) projection. If you would use Perspective projection, then the projected size of the object would decrease, when the distance to the point of view increases. Perspective projection can be set by gluPerspective. e.g.:
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(90.0, (double)windowWidth / windowHeight, 0.1, 600.0);
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<GL/glut.h>
double cameraAngle;
void grid_and_axes() {
// draw the three major AXES
glBegin(GL_LINES);
//X axis
glColor3f(0, 1, 0); //100% Green
glVertex3f(-150, 0, 0);
glVertex3f(150, 0, 0);
//Y axis
glColor3f(0, 0, 1); //100% Blue
glVertex3f(0, -150, 0); // intentionally extended to -150 to 150, no big deal
glVertex3f(0, 150, 0);
//Z axis
glColor3f(1, 1, 1); //100% White
glVertex3f(0, 0, -150);
glVertex3f(0, 0, 150);
glEnd();
//some gridlines along the field
int i;
glColor3f(0.5, 0.5, 0.5); //grey
glBegin(GL_LINES);
for (i = -10; i <= 10; i++) {
if (i == 0)
continue; //SKIP the MAIN axes
//lines parallel to Y-axis
glVertex3f(i * 10, -100, 0);
glVertex3f(i * 10, 100, 0);
//lines parallel to X-axis
glVertex3f(-100, i * 10, 0);
glVertex3f(100, i * 10, 0);
}
glEnd();
}
void display() {
//codes for Models, Camera
//clear the display
//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0, 0, 0, 0); //color black
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //clear buffers to preset values
/***************************
/ set-up camera (view) here
****************************/
//load the correct matrix -- MODEL-VIEW matrix
glMatrixMode(GL_MODELVIEW); //specify which matrix is the current matrix
//initialize the matrix
glLoadIdentity(); //replace the current matrix with the identity matrix [Diagonals have 1, others have 0]
//now give three info
//1. where is the camera (viewer)?
//2. where is the camera looking?
//3. Which direction is the camera's UP direction?
//gluLookAt(0,-150,20, 0,0,0, 0,0,1);
gluLookAt(150 * sin(cameraAngle), -150 * cos(cameraAngle), 50, 0, 0, 0, 0, 0, 1);
/*************************
/ Grid and axes Lines
**************************/
grid_and_axes();
/****************************
/ Add your objects from here
****************************/
/*glColor3f(1, 0, 0);
glutSolidCone(20, 20, 20, 20);
glColor3f(0, 0, 1);
GLUquadricObj *cyl = gluNewQuadric();
gluCylinder(cyl, 10, 10, 50, 20, 20);
glTranslatef(0, 0, 50);
glColor3f(1, 0, 0);
glutSolidCone(10, 20, 20, 20);
*/
glColor3f(1, 0, 0);
glutSolidCube(1);
I am not getting any cube here.
However if I use any transformation property like scaling or rotate then I get the desired cube like
glColor3f(1, 0, 0);
glScalef(50,5,60);
glutSolidCube(1);
what is the problem?
Another problem I am facing that color doesn't work if i don't use transformation property like above mentioned. If I write:
glColor3f(1, 0, 0);
glutSolidCone(20, 20, 20, 20);
For above codes color doesn't work; i get the default colored cone
However if I change this two lines to these 3 lines then color works perfectly:
glColor3f(1,0,0);
glTranslatef(0, 0, 50);
glutSolidCone(10,20,20,20);
then color works; what is the problem? Please help
//ADD this line in the end --- if you use double buffer (i.e. GL_DOUBLE)
glutSwapBuffers();
}
void animate() {
//codes for any changes in Models, Camera
cameraAngle += 0.001; // camera will rotate at 0.002 radians per frame.
//codes for any changes in Models
//MISSING SOMETHING? -- YES: add the following
glutPostRedisplay(); //this will call the display AGAIN
}
void init() {
//codes for initialization
cameraAngle = 0; //angle in radian
//clear the screen
glClearColor(0, 0, 0, 0);
/************************
/ set-up projection here
************************/
//load the PROJECTION matrix
glMatrixMode(GL_PROJECTION);
//initialize the matrix
glLoadIdentity();
/*
gluPerspective() — set up a perspective projection matrix
fovy - Specifies the field of view angle, in degrees, in the y direction.
aspect ratio - Specifies the aspect ratio that determines the field of view in the x direction. The aspect ratio is the ratio of x (width) to y (height).
zNear - Specifies the distance from the viewer to the near clipping plane (always positive).
zFar - Specifies the distance from the viewer to the far clipping plane (always positive).
*/
gluPerspective(70, 1, 0.1, 10000.0);
}
int main(int argc, char **argv) {
glutInit(&argc, argv); //initialize the GLUT library
glutInitWindowSize(500, 500);
glutInitWindowPosition(100, 100);
/*
glutInitDisplayMode - inits display mode
GLUT_DOUBLE - allows for display on the double buffer window
GLUT_RGBA - shows color (Red, green, blue) and an alpha
GLUT_DEPTH - allows for depth buffer
*/
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGB);
glutCreateWindow("Some Title");
init(); //codes for initialization
glEnable(GL_DEPTH_TEST); //enable Depth Testing
glutDisplayFunc(display); //display callback function
glutIdleFunc(animate); //what you want to do in the idle time (when no drawing is occuring)
glutMainLoop(); //The main loop of OpenGL
return 0;
}
I am not getting any cube here.
You do get a cube. It is just that tiny speck where the axis intersect. What else would you expect to see when you draw something 2 units big, ~160 units away, with a 70 degree field of view?
Another problem I am facing that color doesn't work if i don't use transformation property like above mentioned.
[...] I get the default colored cone.
I've no idea what you even mean by that. The "default color" would be the initial value of GL's builtin color attribute - which is (1, 1, 1, 1) - white. With the code you have set up, you will get the color which you set before. So the only guess I can make here is that you confused yourself by not properly taking GL's state machine into account.
But besides all that, you should not use that code at all - this is using the fixed function pipeline and immediate mode drawing - features which are deprecated since a decade now, and not supported at all by modern core profiles of OpenGL. Trying to learn that stuff in 2017 is a waste of time. And btw:
glutMainLoop(); //The main loop of OpenGL
Nope. Just NO!!!. OpenGL does not have a "main loop". GLUT is not OpenGL. Honestly, this is all just horrible.
My program refuses to do depth testing. The two sphere objects are always drawn in the order they are created, not according to their position. Sphere alpha is positioned at (0, 0, 1) and Sphere beta is positioned (0, 0, -10), yet OpenGL still draws beta on top of alpha. I set depth test to enabled in my program.
Nothing appears to work. I want OpenGL to do depth test automatically on any objects drawn in the window. Any help or advise would be greatly appreciated. Here is the full code.
#include "GL/freeglut.h"
#include "GL/gl.h"
#include "GL/glu.h"
const int SPHERE_RES = 200;
double Z_INIT = -28.0;
double RADIUS = 2;
double Red[3] = {1, 0, 0};
double Blue[3] = {0, 0, 1};
using namespace std;
/*
* Method handles resize of the window
*/
void handleResize (int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
double ratio = (float)w/ (float)h;
gluPerspective(45.0, ratio, 1.0, 100.0);
}
/*
* Color and depth is enabled and in this method
*/
void configureColor(void)
{
glClearColor(1.0f, 1.0f, 1.0f, 0.0f); //Set background to white
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear window.
glDepthFunc(GL_ALWAYS);
glEnable(GL_DEPTH_TEST);
glEnable(GL_COLOR_MATERIAL);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
}
void display (void) {
configureColor();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
GLfloat sun_direction[] = { 0.0, 0.0, -1.0, 0.0};
glLightfv(GL_LIGHT0, GL_POSITION, sun_direction);
GLUquadric* quad = gluNewQuadric();
//first sphere is drawn
glColor3f(Red[0], Red[1], Red[2]);
glPushMatrix();
glLoadIdentity();
glTranslatef(0, 0, Z_INIT);
glTranslatef(0, 0, 1.0);
gluSphere(quad, RADIUS, SPHERE_RES, SPHERE_RES);
glPopMatrix();
//second sphere is supposed to be drawn behind it,
//but it is drawn on top.
glColor3f(Blue[0], Blue[1], Blue[2]);
glPushMatrix();
glLoadIdentity();
glTranslatef(0, 0, Z_INIT);
glTranslatef(0, 0, -10.0);
gluSphere(quad, RADIUS, SPHERE_RES, SPHERE_RES);
glPopMatrix();
free(quad);
glFlush();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv); //initializes the GLUT
glutInitDisplayMode(GLUT_SINGLE);
glutInitWindowSize(600,600);
glutInitWindowPosition(100,100);
glutCreateWindow("OpenGL - First window demo");
glutReshapeFunc(handleResize);
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
I am using Ubuntu 14.04 operating system.
glDepthFunc(GL_ALWAYS);
This is the reason you see the spheres in the order they are drawn. Setting the depth function to GL_ALWAYS simply means all depth tests always pass, for any fragment, be it closer or farther.
You need GL_LESS for the result you want. A fragment having depth lesser than the one in the frame buffer wins; the closer (lesser z) one wins over the farther (greater z) one.
You can either call glDepthFunc(GL_LESS) or comment out glDepthFunc(GL_ALWAYS) since GL_LESS is the default.
The program should simulate a planet rotating around another planet.
I use gltranslatef to let the planet move around the bigger planet, but the problem is that the planet should hide when is over the bigger planet, because dz is -0.5.
But if I test the program I always see the red planet over the blue one.
Another problem I have: the planet rotates too fast, how do I slow it?
#include <OpenGL/OpenGL.h>
#include <GLUT/GLUT.h>
#include "utility.h"
GLfloat dx=0.0;
GLfloat dz=-0.5;
bool plus=true;
void init()
{
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glLoadIdentity();
glOrtho(-1, 1, -1, 1, -1, 1);
glEnable(GLUT_DEPTH);
}
void render()
{
glClearColor(BLACK);
glClear(GL_COLOR_BUFFER_BIT);
glColor4f(BLUE);
glutWireSphere(0.25, 100, 100);
glPushMatrix();
glLoadIdentity();
glTranslatef(-0.5+dx, 0.0, -dz);
glColor4f(RED);
glutWireSphere(0.05, 100, 100);
glPopMatrix();
glFlush();
}
void idle()
{
if(plus)
{
dx+=0.05;
}
else
{
dx-=0.05;
}
if(dx>=1.0)
{
dx=0.5;
plus=false;
}
else if(dx<=-0.0)
{
dx=0.0;
plus=true;
}
glutPostRedisplay();
}
int main(int argc, const char * argv[])
{
glutInit(&argc, (char**)argv);
glutInitWindowSize(500, 500);
glutInitWindowPosition(150, 150);
glutInitWindowPosition(0, 0);
glutCreateWindow("Simple");
glutIdleFunc(idle);
init();
glutDisplayFunc(render);
glutMainLoop();
return 0;
}
I haven't understood well how does the idle function work, why it gets called so many times? Can't I choose a time interval with which the idle function gets called?
More info: RED and BLUE are RGB floats, defined in the utility.h header file.
plus is a bool that is used to know if I have to decrease or increase dx.
Give this a shot:
#include <GL/glut.h>
double GetSeconds()
{
return glutGet(GLUT_ELAPSED_TIME) / 1000.0f;
}
void render()
{
glClearColor(0,0,0,0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3ub(0,0,255);
glutWireSphere(0.25, 100, 100);
glPushMatrix();
glLoadIdentity();
static double prv = GetSeconds();
double cur = GetSeconds();
double delta = cur - prv;
prv = cur;
const float DEG_PER_SEC = 60.0f;
static float angle = 0.0f;
angle += DEG_PER_SEC * delta;
while( angle > 360 ) angle -= 360;
glPushMatrix();
glRotatef( angle, 0, 1, 0 );
glTranslatef( 0.5, 0, 0);
glColor3ub(255,0,0);
glutWireSphere(0.05, 100, 100);
glPopMatrix();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1, 1, -1, 1, -1, 1);
}
void timer(int extra)
{
glutPostRedisplay();
glutTimerFunc(16, timer, 0);
}
int main(int argc, const char * argv[])
{
glutInit(&argc, (char**)argv);
glutInitWindowSize(500, 500);
glutInitWindowPosition(150, 150);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Simple");
glutReshapeFunc(reshape);
glutTimerFunc(0, timer, 0);
glutDisplayFunc(render);
glEnable( GL_DEPTH_TEST );
glutMainLoop();
return 0;
}
Important parts:
Explicit glMatrixMode() calls
Calling glutInitDisplayMode() before glutCreateWindow()
Double-buffering requires glutSwapBuffers()
Clearing the depth buffer via GL_DEPTH_BUFFER_BIT
glEnable( GL_DEPTH_TEST )
glRotatef() for planet rotation
Timer-based animation