Fixing glRasterPos() position? - c

Question

I am working on a OPENGL with C project. In this project, a ball will be there and it will have random motion, colliding with the walls of window and moving in a random direction. the player needs to click on the ball and the score which is displayed on top left corner will be incremented by 1 and the speed of the ball will increase by 1. We also have timer displayed on top right of 1 min. After 1 min the game will be over and the final score will be displayed to the player.
So far I have done the random motion of the ball. Score text displayed. The problem is that score is moving with the ball, it is not static on the top left corner. So how to do it?
Here is my code:
#include<GL/glut.h>
#include<math.h>
#include<stdbool.h>
#define PI 3.14159265f
//Variable defined outside globally
GLfloat ballRadius = 0.2; //Radius of the bouncing ball
GLfloat ballX = 0.0f; //Ball's center(x,y) position
GLfloat ballY = 0.0f;
GLfloat ballXMax,ballXMin,ballYMax,ballYMin; //Ball's center (x,y) bounds
GLfloat xSpeed = 0.02f; //Ball's speed in x and y direction
GLfloat ySpeed = 0.007f;
int refreshMills = 30;
int x1,xa,ya; //refresh period in milliseconds
int score=0;
int last_mx = 0, last_my = 0, cur_mx = 0, cur_my = 0;
int arcball_on = false;
//Projection clipping area
GLdouble clipAreaXLeft,clipAreaXRight,clipAreaYBottom,clipAreaYTop;
// Initialize OpenGL Graphics
void initGL()
{
glClearColor(0.0,0.0,0.0,1.0); //Set background(clear) color to green
}
// Callback handler for window re-paint event
void display()
{
glClear(GL_COLOR_BUFFER_BIT); //Clear the color buffer
glMatrixMode(GL_MODELVIEW); //To operate on the model-view matrix
glLoadIdentity(); //Reset model-view matrix
glTranslatef(ballX,ballY,0.0f); //Translate to (xPos,yPos)
glBegin(GL_TRIANGLE_FAN); //Use triangular segments to form a circle
glColor3ub( rand()%1000, rand()%1000, rand()%1000 ); //Red
glVertex2f(0.0f,0.0f); //Center of circle
int numSegments = 100; //ball shape temp...
GLfloat angle;
int i;
for(i=0;i<=numSegments;i++) //Last vertex same as first vertex
{
angle = i*2.0f*PI/numSegments; //360 degree for all segments
glVertex2f(cos(angle)*ballRadius,sin(angle)*ballRadius);
}
glEnd();
glFlush(); //Swap front and back buffers
//Animation Control - compute the location for next refresh
ballX += xSpeed;
ballY += ySpeed;
//Check if the ball exceeds the edges
if(ballX > ballXMax)
{ xa=ballX;
ballX = ballXMax;
xSpeed = -xSpeed;
}
else if(ballX < ballXMin)
{ xa=ballX;
ballX = ballXMin;
xSpeed = -xSpeed;
}
if(ballY > ballYMax)
{ ya=ballY;
ballY = ballYMax;
ySpeed = -ySpeed;
}
else if(ballY < ballYMin)
{ ya=ballY;
ballY = ballYMin;
ySpeed = -ySpeed;
}
glColor3f(1.0,0.0,0.0);
glRasterPos2f(-1.0,0.0);
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'S');
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'C');
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'O');
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'R');
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'E');
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,':');
glFlush();
}
void onMouse(int button, int state, int x, int y) {
if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
arcball_on = true;
last_mx = cur_mx = x;
last_my = cur_my = y;
} else {
arcball_on = false;
if(cur_mx==x && cur_my==y)
{
score=score+1;
}
printf("%d",score);
}
}
void onMotion(int x, int y) {
if (arcball_on) { // if left button is pressed
cur_mx = x;
cur_my = y;
}
}
/*void mouseClicks(int button, int state, int x, int y) {
if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
utton == GLUT_RIGHT_BUTTON && state == GLUT_DOWN) {
}
*/
//Call back when the windows is re-sized
void reshape(GLsizei width,GLsizei height)
{
//Compute aspect ratio of the new window
if(height ==0) height = 1; //To prevent divide by 0
GLfloat aspect = (GLfloat)width / (GLfloat)height;
//Set the viewport to cover the new window
glViewport(0,0,width,height);
//Set the aspect ratio of the clipping area to match the viewport
glMatrixMode(GL_PROJECTION); //To operate on the Projection matrix
glLoadIdentity(); //Reset the Projection Matrix
if(width >=height)
{
clipAreaXLeft = -1.0 * aspect;
clipAreaXRight = 1.0 * aspect;
clipAreaYBottom = -1.0;
clipAreaYTop = 1.0;
}
else
{
clipAreaXLeft = -1.0;
clipAreaXRight = 1.0 ;
clipAreaYBottom = -1.0 / aspect;
clipAreaYTop = 1.0 / aspect;
}
gluOrtho2D(clipAreaXLeft,clipAreaXRight,clipAreaYBottom,clipAreaYTop+0.25);
ballXMin = clipAreaXLeft + ballRadius;
ballXMax = clipAreaXRight - ballRadius;
ballYMin = clipAreaYBottom + ballRadius;
ballYMax = clipAreaYTop - ballRadius;
}
//Call back when the timer expired
void Timer(int value)
{
glutPostRedisplay(); //Post a paint request to activate display()
glutTimerFunc(refreshMills,Timer,5); //subsequent timer call at milliseconds
}
int windowWidth = 500; //Window mode's width
int windowHeight = 500; //Window mode's height
int windowPosX = 100; //Window mode's top-left corner x
int windowPosY = 100;
//Main function: GLUT runs as a console application starting at main()
int main(int argc,char* argv[])
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB); //Enable double buffered mode
glutInitWindowSize(windowWidth,windowHeight); //Initial window width and height
glutInitWindowPosition(windowPosX,windowPosY); //Initial window top-left corner(x,y)
glutCreateWindow("Bouncing Ball");
glutMouseFunc(onMouse);
glutMotionFunc(onMotion);
glutDisplayFunc(display); //Register callback handler for window re-paint
//glutMouseFunc(mouseClicks);
glutReshapeFunc(reshape);
glutPostRedisplay(); //Register callback handler for window re-shape
glutTimerFunc(0,Timer,0); //First timer call immediately
initGL(); //Our own OpenGL initialization
glutMainLoop(); //Enter event processing loop
}

Answer 1

Omitting the drawing code for the ball, you have this code sequence:
glLoadIdentity(); //Reset model-view matrix
glTranslatef(ballX,ballY,0.0f); //Translate to (xPos,yPos)
...
glRasterPos2f(-1.0,0.0);
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'S');
The current modelview transformation is applied to the position you specify with glRasterPos2f(), which includes the translation you specified with glTranslatef().
You have a few options to fix this:
Reset the transformation before calling glRasterPos2f():
glLoadIdentity();
glRasterPos2f(-1.0,0.0);
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'S');
Push/pop the transformation you use for drawing the ball, to restore the previous transformation after you finished drawing the ball:
glLoadIdentity(); //Reset model-view matrix
glPushMatrix();
glTranslatef(ballX,ballY,0.0f); //Translate to (xPos,yPos)
...
glPopMatrix();
glRasterPos2f(-1.0,0.0);
glutBitmapCharacter (GLUT_BITMAP_8_BY_13,'S');
Use glWindowPos() instead of glRasterPos(), which allows you to specify the position in pixels, instead of coordinates that will be transformed.