Want to move one 2d object and not the other - c++

Question

I have to make a bowling game in openGL. This is the code I have so far. What it does that it draws a ball and is moved accordingly when an arrow key is pressed.
So far, I have that ball moving, that is fine. What I want to do that other point I have created, that should not be moved. Because, when that ball reaches to that point, it should be drop or something I will make that obstacle is dropped.
The code is written in Eclipse IDE.
#include <stdio.h>
#include <GL/glut.h>
#include <math.h>
#include <stdio.h> /* printf, scanf, puts, NULL */
float posX = 0, posY = -0.1, posZ = 0;
GLfloat rotation = 90.0;
double x, y, angle;
#define PI 3.1415926535898
GLint circle_points = 50;
void reshape(int width, int heigth) {
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
//clip the windows so its shortest side is 2.0
if (width < heigth) {
glOrtho(-2.0, 2.0, -2.0 * (GLfloat) heigth / (GLfloat) width,
2.0 * (GLfloat) heigth / (GLfloat) width, 2.0, 2.0);
} else {
glOrtho(-2.0, 2.0, -2.0 * (GLfloat) width / (GLfloat) heigth,
2.0 * (GLfloat) width / (GLfloat) heigth, 2.0, 2.0);
}
// set viewport to use the entire new window
glViewport(0, 0, width, heigth);
}
void circ() {
glColor3f(0.0, 0.0, 1.0);
glPointSize(11.0);
glBegin(GL_POINTS);
glVertex3f(0.1, 0.1, 0.0);
glEnd();
glBegin(GL_TRIANGLE_FAN);
for (int i = 0; i <= 300; i++) {
angle = 2 * PI * i / 300;
x = cos(angle) / 20;
y = sin(angle) / 20;
glVertex2d(x, y);
}
glEnd();
}
void display() {
//Clear Window
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glTranslatef(posX, posY, posZ);
circ();
glPopMatrix();
glFlush();
}
void init() {
// set clear color to black
glClearColor(1.0, 1.0, 1.0, 0.0);
// set fill color to white
glColor3f(1.0, 1.0, 1.0);
//This is the default view and these statements could be removed
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-1.0, 1.0, -1.0, 1.0);
}
float move_unit = 0.02f;
void keyboardown(int key, int x, int y) {
switch (key) {
case GLUT_KEY_RIGHT:
posX += move_unit;
break;
case GLUT_KEY_LEFT:
posX -= move_unit;
break;
case GLUT_KEY_UP:
posY += move_unit;
break;
case GLUT_KEY_DOWN:
posY -= move_unit;
break;
default:
break;
}
glutPostRedisplay();
}
int main(int argc, char** argv) {
//initialize mode and open a windows in upper left corner of screen
//Windows tittle is name of program
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(600, 500);
glutInitWindowPosition(0, 0);
glutCreateWindow("Practice 1");
glutDisplayFunc(display);
init();
glutSpecialFunc(keyboardown);
glutMainLoop();
}

Answer 1

Modern graphics APIs simulating finite state machine. That means that before Draw calls you must fully configure (or leave default) graphics pipeline "machine":
SetStates(); // Configure pipeline state: set geometry, textures, matrices, etc.
Begin();
Draw(); // Render frame according to current pipeline configuration (state)
End(); // Swap screen buffers
In case of many objects, you can just wrap all stuff with for loop:
for( each_object )
{
SetStates(); // current object's vertex/index buffer, texture, matrices, etc.
Begin();
Draw();
End();
}
Not very efficient. Next step of improvement might include: frustum culling, instancing, vertex buffers merging, texture atlases, draw calls sorting, etc.
BTW, consider using Vertex Buffer Objects (VBOs), instead of Begin/glVertex2d/End which is deprecated

Answer 2

Try this:
#include <GL/glut.h>
#include <cmath>
float posX = 0, posY = -0.1, posZ = 0;
GLfloat rotation = 90.0;
double x, y, angle;
#define PI 3.1415926535898
GLint circle_points = 50;
void point()
{
glColor3f(0.0, 0.0, 1.0);
glPointSize(11.0);
glBegin(GL_POINTS);
glVertex3f(0.1, 0.1, 0.0);
glEnd();
}
void circ()
{
glColor3f(0.0, 0.0, 1.0);
glBegin(GL_TRIANGLE_FAN);
for (int i = 0; i <= 300; i++)
{
angle = 2 * PI * i / 300;
x = cos(angle) / 20;
y = sin(angle) / 20;
glVertex2d(x, y);
}
glEnd();
}
void display()
{
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-1.0, 1.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
point();
glPopMatrix();
glPushMatrix();
glTranslatef(posX, posY, posZ);
circ();
glPopMatrix();
glutSwapBuffers();
}
float move_unit = 0.02f;
void keyboardown(int key, int x, int y)
{
switch (key)
{
case GLUT_KEY_RIGHT:
posX += move_unit;
break;
case GLUT_KEY_LEFT:
posX -= move_unit;
break;
case GLUT_KEY_UP:
posY += move_unit;
break;
case GLUT_KEY_DOWN:
posY -= move_unit;
break;
default:
break;
}
glutPostRedisplay();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(600, 500);
glutInitWindowPosition(0, 0);
glutCreateWindow("Practice 1");
glutDisplayFunc(display);
glutSpecialFunc(keyboardown);
glutMainLoop();
}