I made this code for a bounce ball around the screen, as it turns out it doesn't work as I spected.
I am working in OpenGL with glut and c++.
My question is: How can I stop the flickering on the run?
#include "stdafx.h"
#include <Windows.h>
#include <GL\glut.h>
#include <math.h>
#define PI 3.14159265f
GLfloat radius_Bolita= 1.0f;
GLfloat posX_Bolita = 0.0f;
GLfloat posY_Bolita = 0.0f;
GLfloat xSpeed_Bolita = 0.02f;
GLfloat ySpeed_Bolita = 0.007f;
GLfloat xmaxBound_Bolita, xminBound_Bolita, ymaxBound_Bolita, yminBound_Bolita;
int updateMS = 30;
GLdouble areaClip_Xleft, areaClip_Xright, areaClip_Ytop, areaClip_Ybottom;
void initOpenGL(){
glClearColor(1.0, 1.0, 0.0, 1.0); //color de fondo
}
void pantalla() {
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(posX_Bolita, posY_Bolita, 0.0f);
glBegin(GL_TRIANGLE_FAN);
glColor3f(1.0, 1.0, 1.0); //color de bolita
glVertex2d(0.0f, 0.0f);
int partes=100;
GLfloat angulo;
for (int i = 0; i < partes; i++) {
angulo = i * 2.0f * PI / partes;
glVertex2d(cos(angulo)*radius_Bolita,sin(angulo)*radius_Bolita);
}
glEnd;
glutSwapBuffers();
posX_Bolita += xSpeed_Bolita;
posY_Bolita += ySpeed_Bolita;
if (posX_Bolita > xmaxBound_Bolita) {
posX_Bolita = xmaxBound_Bolita;
xSpeed_Bolita = -xSpeed_Bolita;
}
else if(posX_Bolita < xminBound_Bolita){
posX_Bolita = xminBound_Bolita;
xSpeed_Bolita = -xSpeed_Bolita;
}
if (posY_Bolita > ymaxBound_Bolita) {
posY_Bolita = ymaxBound_Bolita;
ySpeed_Bolita = -ySpeed_Bolita;
}
else if (posY_Bolita < yminBound_Bolita) {
posY_Bolita = yminBound_Bolita;
ySpeed_Bolita = -ySpeed_Bolita;
}
}
void ajustar(GLsizei width, GLsizei height) {
if (height=0) {
height = 1;
}
GLfloat look = (GLfloat)width / (GLfloat)height;
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if (width >= height) {
areaClip_Xleft= -1.0 * look;
areaClip_Xright= 1.0 * look;
areaClip_Ybottom= -1.0;
areaClip_Ytop= 1.0;
}
else {
areaClip_Xleft = -1.0;
areaClip_Xright = 1.0;
areaClip_Ybottom = -1.0/look;
areaClip_Ytop = 1.0/look;
}
gluOrtho2D(areaClip_Xleft, areaClip_Xright, areaClip_Ybottom, areaClip_Ytop);
xminBound_Bolita = areaClip_Xleft + radius_Bolita;
xmaxBound_Bolita= areaClip_Xright - radius_Bolita;
yminBound_Bolita= areaClip_Ybottom + radius_Bolita;
ymaxBound_Bolita= areaClip_Ytop - radius_Bolita;
}
void tempo(int value) {
glutPostRedisplay();
glutTimerFunc(updateMS, tempo, 0);
}
int window_Width=640;
int window_Height=480;
int window_Posx=50;
int window_Posy=50;
int main(int argc,char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE);
glutInitWindowSize(window_Width,window_Height);
glutInitWindowPosition(window_Posx, window_Posy);
glutCreateWindow("BouncyBall");
glutDisplayFunc(pantalla);
glutReshapeFunc(ajustar);
glutTimerFunc(0,tempo,0);
initOpenGL();
glutMainLoop();
return 0;
}
As you can see, I tried the doubleBuffer stuff, didn't work. Maybe I did it wrong
glutSwapBuffers();
Well it turns out as I'm still a noob here i did not debugged this code the right way, thankfully to #andreas and #genpfault I was able to solve it. Thanks to all of you. The solution was not having used glEnd() at the end of my file... so yeah kind of a sneaky error.
Related
I am trying to scroll a text as a banner. I used openGL with glut to make this work. The whole code works if I use a figure like a square. The square scrolls over the screen.
Now I want to do this with text. Every time this program started. The text came at its starting position, but when the timer starts, it vanished. This is probably because the screen was cleared every clocktick, but the screen doesn't build up again.
Someone who can help me with this translation animation and text?
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <iostream>
#ifdef WIN32
#include <windows.h>
#endif
#include <GL/gl.h>
#include <GL/glut.h>
using namespace std;
static int font_index = 0;
int state = 1;
void print_bitmap_string(/*void* font,*/ const char* s)
{
while (*s) {
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *s);
s++;
}
}
void my_reshape(int w, int h)
{
GLdouble size;
GLdouble aspect;
/* Use the whole window. */
glViewport(0, 0, w, h);
/* We are going to do some 2-D orthographic drawing. */
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
size = (GLdouble)((w >= h) ? w : h) / 2.0;
if (w <= h) {
aspect = (GLdouble)h / (GLdouble)w;
glOrtho(-size, size, -size * aspect, size * aspect, -100000.0, 100000.0);
}
else {
aspect = (GLdouble)w / (GLdouble)h;
glOrtho(-size * aspect, size * aspect, -size, size, -100000.0, 100000.0);
}
/* Make the world and window coordinates coincide so that 1.0 in */
/* model space equals one pixel in window space. */
glScaled(aspect, aspect, 1.0);
/* Now determine where to draw things. */
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
float yild;
float ystep;
float x_pos = -200;
float y_pos = 70;
void draw()
{
const char* bitmap_font_names[7] = { "Hello train" };
/* Draw the strings, according to the current mode and font. */
glTranslatef(0.5, -100, 0);
//set the text color
glColor4f(0.0f, 255.0f, 140.0f, 1.0f);
ystep = 100.0;
yild = 20.0;
glRasterPos2f(x_pos, y_pos + 1.25 * yild);
print_bitmap_string(bitmap_font_names[0]);
}
void display(void)
{
//change background color
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
draw();
glColor3f(0.0, 1.0, 0.0);
glBegin(GL_POLYGON);
glVertex2f(x_pos + 0.5f, 0.0f);
glVertex2f(x_pos+1.0f, 0.5f);
glVertex2f(x_pos+0.5f, 0.5f);
glEnd();
glutSwapBuffers();
}
void timer(int) {
glutPostRedisplay();
glutTimerFunc(1000 , timer, 0);
switch (state) {
case 1:
if (x_pos > -295) {
x_pos -= 1;
}
else {
state = -1;
}
break;
case -1:
x_pos = 180;
state = 1;
break;
}
cout << x_pos << endl;
}
int main(int argc, char** argv)
{
glutInitWindowSize(500, 150);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
glutCreateWindow("Train Display");
glutDisplayFunc(display);
glutReshapeFunc(my_reshape);
glutTimerFunc(1000, timer, 0);
glutMainLoop();
return 0;
}
glTranslate does not just set a translation matrix, but multiply the current matrix by a translation matrix. You need to load the identity matrix with glLoadIdentity before glTranslatef or save and restore the current matrix with glPushMatrix/glPopMatrix:
void draw()
{
const char* bitmap_font_names[7] = { "Hello train" };
glPushMatrix();
/* Draw the strings, according to the current mode and font. */
glTranslatef(0.5, -100, 0);
//set the text color
glColor4f(0.0f, 255.0f, 140.0f, 1.0f);
ystep = 100.0;
yild = 20.0;
glRasterPos2f(x_pos, y_pos + 1.25 * yild);
print_bitmap_string(bitmap_font_names[0]);
glPopMatrix();
}
#include <stdio.h> // this library is for standard input and output
#include "glut.h"// this library is for glut the OpenGL Utility Toolkit
#include <math.h>
float squareX = 0.0f;
float squareY = -0.3f;
float squareZ = 0.0f;
static int flag = 1;
void drawShape(void) {
glTranslatef(squareX, squareY, squareZ);
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex2f(162, 50);
glVertex2f(162, 10);
glVertex2f(220, 10);
glVertex2f(220, 50);
glVertex2f(162, 50);
glEnd();
}
void initRendering() {
glEnable(GL_DEPTH_TEST);
}
// called when the window is resized
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0f, (float)w, 0.0f, (float)h, -1.0f, 1.0f);
}
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
drawShape();
glutSwapBuffers();
}
// make the square go up
void update(int value) {
if (flag) {
squareY += 1.0f;
if (squareY > 400.0) {
flag = 0;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
}
// make the square go right
/* void update(int value) {
if (flag) {
squareX += 1.0f;
if (squareX > 400.0) {
flag = 0;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
} */
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
glutCreateWindow("Moving Square");
initRendering();
glutDisplayFunc(drawScene);
glutReshapeFunc(handleResize);
glutTimerFunc(25, update, 0);
glutMainLoop();
return(0);
}
I have uploaded this code before but this time I made the square go all the way up. The code just moves the square up, but I don't know how to position it on the left once it reaches the top, so then I can make it move to the right. I have uploaded a demonstration on how I want it to look below.
Preview:
What I want it to do next:
I recommend to initialize the variables squareX, squareY and squareZ with the start position of the rectangle:
float squareX = 162.0f;
float squareY = 0.0f;
float squareZ = 0.0f;
Do not draw a rectangle specific position, but draw a rectangle on the position (0,0) with a length (width, height). Let the model matrix (set by glTranslatef), do the job of the positioning:
void drawShape(void)
{
float width = 58.0f;
float height = 40.0f;
glTranslatef(squareX, squareY, squareZ);
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex2f(0, 0);
glVertex2f(width, 0);
glVertex2f(width, height);
glVertex2f(0, height);
glVertex2f(0, 0);
glEnd();
}
Use a variable state, which has stated the direction of the current movement:
int state = 1; // 0: stop; 1: move up; 2: move right
If the rectangle a certain position has reached, then the state has to be changed and a the new start position can be set. At the final position, the rectangle can stop or the process can even be restarted:
void update(int value)
{
if (state == 1) // 1 : move up
{
squareY += 1.0f;
if (squareY > 400.0)
{
state = 2;
squareX = 0.0f;
squareY = 180.0f;
}
}
else if (state == 2) // 2 : move right
{
squareX += 1.0f;
if (squareX > 400.0)
{
state = 0;
// restart
//state = 1;
//squareX = 162.0f;
//squareY = 0.0f;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
}
I'm trying to code a camera with glTranslate/glRotate. To implement the look-up / look-down functions I need all the objects in my rendering space to rotate around a point (that is, where the "camera" is at), point which usually differs from the origin. Still, things keep rotating around the origin. Is there a way to specify a different point?
EDIT: Added code
Thanks for your fast reply. It seems that I can't get it working right no matter what, so I've decided to add my code; I'd much appreciate if someone could take a look at it and tell me what changes are needed in order to translate/rotate/translate back.
#include <iostream>
#include <cmath>
#include <GLUT/GLUT.h>
const double roaming_step = .13;
double z_offset = .0;
double y_offset = .0;
double x_offset = .0;
const double angle_step = 1.5;
double angle_xz = .0;
double angle_yz = .0;
bool keyStates[256] = { false };
void drawFloor()
{
glColor3f(1.0, 1.0, 1.0);
glBegin(GL_QUADS);
glVertex3f(-3.0, -1.0, 3.0);
glVertex3f(-3.0, -1.0, -3.0);
glVertex3f(3.0, -1.0, -3.0);
glVertex3f(3.0, -1.0, 3.0);
glEnd();
}
void drawBalls()
{
glTranslatef(-3.0, -.5, -3.0);
glColor3f(.8, .1, .1);
for(int i = 0; i < 3; i++)
{
glPushMatrix();
glTranslatef(.0, -.5, i * 3);
for(int j = 0; j < 3; j++)
{
glPushMatrix();
glTranslatef(j * 3, .0, .0);
glutSolidSphere(.5, 20, 20);
glPopMatrix();
}
glPopMatrix();
}
}
void keyPressed(unsigned char key, int x, int y)
{
keyStates[key] = true;
}
void keyReleased(unsigned char key, int x, int y)
{
keyStates[key] = false;
}
void keyboardOperations()
{
if(keyStates['w'])
z_offset += roaming_step;
if(keyStates['s'])
z_offset -= roaming_step;
if(keyStates['a'])
x_offset += roaming_step;
if(keyStates['d'])
x_offset -= roaming_step;
if(keyStates['i'])
{
angle_xz -= angle_step;
if(angle_xz < .0)
angle_xz += 360.0;
}
if(keyStates['o'])
{
angle_xz += angle_step;
if(angle_xz >= 360.0)
angle_xz -= 360.0;
}
if(keyStates['u'])
{
angle_yz -= angle_step;
if(angle_yz < .0)
angle_yz += 360.0;
}
if(keyStates['j'])
{
angle_yz += angle_step;
if(angle_yz >= 360.0)
angle_yz -= 360.0;
}
if(keyStates['q'])
exit(0);
}
// I guess it has to be done in this function
// but didn't get how
void camera()
{
glLoadIdentity();
// Forward / Backward
glTranslated(.0, .0, z_offset);
// Left / Right
glTranslated(x_offset, .0, .0);
// XZ Rotation
glRotated(angle_xz, .0, 1.0, .0);
// YZ Rotation
glRotated(angle_yz, 1.0, .0, .0);
}
void display(void)
{
keyboardOperations();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
camera();
drawFloor();
drawBalls();
glutSwapBuffers();
}
void reshape(int width, int height)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, width, height);
GLdouble aspect = (GLdouble) width / (GLdouble) height;
gluPerspective(60, aspect, 1, 100);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 500);
glutInitWindowPosition(0, 0);
glutCreateWindow("openGLtest3");
glClearColor(.0, .0, .0, .0);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutIdleFunc(display);
glutIgnoreKeyRepeat(true);
glutKeyboardFunc(keyPressed);
glutKeyboardUpFunc(keyReleased);
glutMainLoop();
return 0;
}
In openGL, glRotation fuction takes origin as a reference. In order to rotate around a point (your camera coordinate in this case) you should translate your camera position to the origin (Translate all your objects accordingly) and then apply rotation function.And then you can translate your camera back (with all your objects)
lets say your camera position is (a,b,c) so your code should be something like :
foreach object
{
glPushMatrix();
glTranslate(a,b,c);
glRotate(...);
glTranslate(-a,-b,-c);
//render
glPopMatrix();
}
My OpenGL program is not working properly. Inside the drawScene() function I created two loops. One loop for GL_LINES another loop for GL_POINTS. The GL_LINES loop works fine but GL_POINTS loop doesn't work. Any help appreciated.
#include <iostream>
#include <stdlib.h>
#include <GL/glut.h>
#include <math.h>
#define PI 3.14159265
using namespace std;
//Called when a key is pressed
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27: //Escape key
exit(0);
}
}
//Initializes 3D rendering
void initRendering() {
glEnable(GL_DEPTH_TEST);
glEnable(GL_COLOR_MATERIAL); //Enable color
glClearColor(0.7f, 0.9f, 1.0f, 1.0f); //Change the background to sky blue
}
//Called when the window is resized
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, (double)w / (double)h, 1.0, 200.0);
}
float _angle = 0.0f;
float _cameraAngle = 0.0f;
float x = -1.5;
float y = -0.5;
//Draws the 3D scene
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glLineWidth (9.0f);
glBegin(GL_LINES);
glColor3f(1.0f, 0.0f, 0.0f);
double r = 0.5;
for(int c = 0;c<=360;c++){
double y = r*cos (c*PI/180);
double x = r*sin (c*PI/180);
glVertex3d(x,y,-5.0);
glVertex3d(0.0,0.0,-5.0);
}
glEnd();
glPointSize (7.0f);
glBegin(GL_POINTS);
glColor3f(0.0f, 1.0f, 0.0f);
double r = 1.0;
for(int c = 0;c<=360;c++){
double y = r*cos (c*PI/180);
double x = r*sin (c*PI/180);
glVertex3d(x,y,-5.0);
//glVertex3d(0.0,0.0,-5.0);
}
glEnd();
glutSwapBuffers();
//glutPostRedisplay();
}
void update(int value) {
_angle += 2.0f;
if (_angle > 360) {
_angle -= 360;
}
glutPostRedisplay();
glutTimerFunc(60, update, 0);
}
int main(int argc, char** argv) {
//Initialize GLUT
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
//Create the window
glutCreateWindow("two circle");
initRendering();
//Set handler functions
glutDisplayFunc(drawScene);
glutKeyboardFunc(handleKeypress);
glutReshapeFunc(handleResize);
glutTimerFunc(25, update, 0); //Add a timer
glutMainLoop();
return 0;
}
Right now, you're declaring the variable r in two places: where you set double r = 0.5; and at double r = 1.0;
Try changing it to:
double r = 0.5;
//First loop
r = 1.0;
//Second loop
I'm trying to draw simple circle with C++/OpenGl
my code is:
#include <GL/glut.h>
#include <math.h>
void Draw() {
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0, 1.0, 1.0);
glBegin(GL_QUADS);
glColor3f (0.0, 0.0, 0.0);
glVertex3f (0.1, 0.1, 0.0);
glVertex3f (0.9, 0.1, 0.0);
glVertex3f (0.9, 0.9, 0.0);
glVertex3f (0.1, 0.9, 0.0);
glEnd();
glFlush();
}
void DrawCircle(float cx, float cy, float r, int num_segments)
{
glBegin(GL_LINE_LOOP);
for(int ii = 0; ii < num_segments; ii++)
{
float theta = 2.0f * 3.1415926f * float(ii) / float(num_segments);//get the current angle
float x = r * cosf(theta);//calculate the x component
float y = r * sinf(theta);//calculate the y component
glVertex2f(x + cx, y + cy);//output vertex
}
glEnd();
}
void Initialize() {
glClearColor(1.0, 1.0, 1.0, 0.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}
int main(int iArgc, char** cppArgv) {
glutInit(&iArgc, cppArgv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(950, 500);
glutInitWindowPosition(200, 200);
glutCreateWindow("Universum");
Initialize();
glutDisplayFunc(Draw);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0, 1.0, 1.0);
DrawCircle(0.5, 0.5, 0.2, 5);
glutMainLoop();
return 0;
}
I'm beginner with OpenGL and now i'm starting to learn,
Can someone please explain me why i don't get the circle (i only see the black box),
Thanks!
It looks like immediately after you draw the circle, you go into the main glut loop, where you've set the Draw() function to draw every time through the loop. So it's probably drawing the circle, then erasing it immediately and drawing the square. You should probably either make DrawCircle() your glutDisplayFunc(), or call DrawCircle() from Draw().
#include <Windows.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define window_width 1080
#define window_height 720
void drawFilledSun(){
//static float angle;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(0, 0, -10);
int i, x, y;
double radius = 0.30;
//glColor3ub(253, 184, 19);
glColor3ub(255, 0, 0);
double twicePi = 2.0 * 3.142;
x = 0, y = 0;
glBegin(GL_TRIANGLE_FAN); //BEGIN CIRCLE
glVertex2f(x, y); // center of circle
for (i = 0; i <= 20; i++) {
glVertex2f (
(x + (radius * cos(i * twicePi / 20))), (y + (radius * sin(i * twicePi / 20)))
);
}
glEnd(); //END
}
void DrawCircle(float cx, float cy, float r, int num_segments) {
glBegin(GL_LINE_LOOP);
for (int ii = 0; ii < num_segments; ii++) {
float theta = 2.0f * 3.1415926f * float(ii) / float(num_segments);//get the current angle
float x = r * cosf(theta);//calculate the x component
float y = r * sinf(theta);//calculate the y component
glVertex2f(x + cx, y + cy);//output vertex
}
glEnd();
}
void main_loop_function() {
int c;
drawFilledSun();
DrawCircle(0, 0, 0.7, 100);
glutSwapBuffers();
c = getchar();
}
void GL_Setup(int width, int height) {
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glEnable(GL_DEPTH_TEST);
gluPerspective(45, (float)width / height, .1, 100);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitWindowSize(window_width, window_height);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
glutCreateWindow("GLUT Example!!!");
glutIdleFunc(main_loop_function);
GL_Setup(window_width, window_height);
glutMainLoop();
}
This is what I did. I hope this helps. Two types of circle are here. Filled and unfilled.
There is another way to draw a circle - draw it in fragment shader.
Create a quad:
float right = 0.5;
float bottom = -0.5;
float left = -0.5;
float top = 0.5;
float quad[20] = {
//x, y, z, lx, ly
right, bottom, 0, 1.0, -1.0,
right, top, 0, 1.0, 1.0,
left, top, 0, -1.0, 1.0,
left, bottom, 0, -1.0, -1.0,
};
Bind VBO:
unsigned int glBuffer;
glGenBuffers(1, &glBuffer);
glBindBuffer(GL_ARRAY_BUFFER, glBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*20, quad, GL_STATIC_DRAW);
and draw:
#define BUFFER_OFFSET(i) ((char *)NULL + (i))
glEnableVertexAttribArray(ATTRIB_VERTEX);
glEnableVertexAttribArray(ATTRIB_VALUE);
glVertexAttribPointer(ATTRIB_VERTEX , 3, GL_FLOAT, GL_FALSE, 20, 0);
glVertexAttribPointer(ATTRIB_VALUE , 2, GL_FLOAT, GL_FALSE, 20, BUFFER_OFFSET(12));
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
Vertex shader
attribute vec2 value;
uniform mat4 viewMatrix;
uniform mat4 projectionMatrix;
varying vec2 val;
void main() {
val = value;
gl_Position = projectionMatrix*viewMatrix*vertex;
}
Fragment shader
varying vec2 val;
void main() {
float R = 1.0;
float R2 = 0.5;
float dist = sqrt(dot(val,val));
if (dist >= R || dist <= R2) {
discard;
}
float sm = smoothstep(R,R-0.01,dist);
float sm2 = smoothstep(R2,R2+0.01,dist);
float alpha = sm*sm2;
gl_FragColor = vec4(0.0, 0.0, 1.0, alpha);
}
Don't forget to enable alpha blending:
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
UPDATE: Read more
We will find the value of X and Y from this image. We know, sinθ=vertical/hypotenuse and cosθ=base/hypotenuse from the image we can say X=base and Y=vertical. Now we can write X=hypotenuse * cosθ and Y=hypotenuse * sinθ.
Now look at this code
void display(){
float x,y;
glColor3f(1, 1, 0);
for(double i =0; i <= 360;){
glBegin(GL_TRIANGLES);
x=5*cos(i);
y=5*sin(i);
glVertex2d(x, y);
i=i+.5;
x=5*cos(i);
y=5*sin(i);
glVertex2d(x, y);
glVertex2d(0, 0);
glEnd();
i=i+.5;
}
glEnd();
glutSwapBuffers();
}
glBegin(GL_POLYGON); // Middle circle
double radius = 0.2;
double ori_x = 0.0; // the origin or center of circle
double ori_y = 0.0;
for (int i = 0; i <= 300; i++) {
double angle = 2 * PI * i / 300;
double x = cos(angle) * radius;
double y = sin(angle) * radius;
glVertex2d(ori_x + x, ori_y + y);
}
glEnd();
Here is a code to draw a fill elipse, you can use the same method but replacing de xcenter and y center with radius
void drawFilledelipse(GLfloat x, GLfloat y, GLfloat xcenter,GLfloat ycenter) {
int i;
int triangleAmount = 20; //# of triangles used to draw circle
//GLfloat radius = 0.8f; //radius
GLfloat twicePi = 2.0f * PI;
glBegin(GL_TRIANGLE_FAN);
glVertex2f(x, y); // center of circle
for (i = 0; i <= triangleAmount; i++) {
glVertex2f(
x + ((xcenter+1)* cos(i * twicePi / triangleAmount)),
y + ((ycenter-1)* sin(i * twicePi / triangleAmount))
);
}
glEnd();
}
I have done it using the following code,
glBegin(GL.GL_LINE_LOOP);
for(int i =0; i <= 300; i++){
double angle = 2 * Math.PI * i / 300;
double x = Math.cos(angle);
double y = Math.sin(angle);
gl.glVertex2d(x,y);
}
glEnd();
glBegin(GL_POLYGON);
double x = 2;
double y = 2;
for (int i = 0; i <= 360; i++) {
glVertex2d(x * sin(i), y * cos(i));
}
glEnd();