How to drag a graph around the window in OpenGL/c++ - c++

Question

below is the code so far, my problem lies in dragging the graph around the window ? i can't seem to do it ? any tips for me guys ?? What i want is when you click and hold down the left mouse button you should be able to drag the graph around the window ?
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>
#if !defined(GLUT_WHEEL_UP)
# define GLUT_WHEEL_UP
# define GLUT_WHEEL_DOWN 4
#endif
/* Set initial size of the display window. */
GLsizei winWidth = 600, winHeight = 600;
/* Set size of world-coordinate clipping window. */
GLfloat xwcMin = -50.0, xwcMax = 50.0;
GLfloat ywcMin = -50.0, ywcMax = 50.0;
bool leftButton;
int downX, downY;
class wcPt3D {
public:
GLfloat x, y, z;
};
void init (void) {
/* Set color of display window to white. */
glClearColor (1.0, 1.0, 1.0, 0.0);
}
void plotPoint (wcPt3D bezCurvePt) {
glBegin (GL_POINTS);
glVertex2f (bezCurvePt.x, bezCurvePt.y);
glEnd ( );
}
/* Compute binomial coefficients C for given value of n. */
void binomialCoeffs (GLint n, GLint * C) {
GLint k, j;
for (k = 0; k <= n; k++) {
/* Compute n!/(k!(n - k)!). */
C [k] = 1;
for (j = n; j >= k + 1; j--)
C [k] *= j;
for (j = n - k; j >= 2; j--)
C [k] /= j;
}
}
void computeBezPt (GLfloat t, wcPt3D * bezPt, GLint nCtrlPts,
wcPt3D * ctrlPts, GLint * C) {
GLint k, n = nCtrlPts - 1;
GLfloat bezBlendFcn;
bezPt->x = bezPt->y = bezPt->z = 0.0;
/* Compute blending functions and blend control points. */
for (k = 0; k < nCtrlPts; k++) {
bezBlendFcn = C [k] * pow (t, k) * pow (1 - t, n - k);
bezPt->x += ctrlPts [k].x * bezBlendFcn;
bezPt->y += ctrlPts [k].y * bezBlendFcn;
bezPt->z += ctrlPts [k].z * bezBlendFcn;
}
}
void bezier (wcPt3D * ctrlPts, GLint nCtrlPts, GLint nBezCurvePts) {
wcPt3D bezCurvePt;
GLfloat t;
GLint *C;
/* Allocate space for binomial coefficients */
C = new GLint [nCtrlPts];
binomialCoeffs (nCtrlPts - 1, C);
for (int i = 0; i <= nBezCurvePts; i++) {
t = GLfloat (i) / GLfloat (nBezCurvePts);
computeBezPt (t, &bezCurvePt, nCtrlPts, ctrlPts, C);
plotPoint (bezCurvePt);
}
delete [ ] C;
}
void displayFcn (void) {
glClear (GL_COLOR_BUFFER_BIT); // Clear display window.
/* Set example number of control points and number of
* curve positions to be plotted along the Bezier curve.
*/ GLint nCtrlPts = 4, nBezCurvePts = 1000;
wcPt3D ctrlPts [4] = { {-40.0, -40.0, 0.0}, {-10.0, 200.0, 0.0},
{10.0, -200.0, 0.0}, {40.0, 40.0, 0.0} };
glPointSize (4);
glColor3f (1.0, 0.0, 0.0); // Set point color to red.
bezier (ctrlPts, nCtrlPts, nBezCurvePts);
glutSwapBuffers();
}
void winReshapeFcn (GLint newWidth, GLint newHeight) {
/* Maintain an aspect ratio of 1.0. */
glViewport (0, 0, xwcMin, ywcMin);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ( );
gluOrtho2D (xwcMin, xwcMax, ywcMin, ywcMax);
glutPostRedisplay();
}
void MouseCallback(int button, int state, int x, int y) {
downX = x;
downY = y;
leftButton = ((button == GLUT_LEFT_BUTTON) && (state == GLUT_DOWN));
glutPostRedisplay();
}
void MotionCallback(int x, int y) {
if (leftButton){
downX=downX+x;
downY=downY+y;
gluOrtho2D (xwcMin, xwcMax, ywcMin, ywcMax);
}
downX = x;
downY = y;
glutPostRedisplay();
}
/*
void MouseCallback(int button, int state, int x, int y) {
if (button == GLUT_WHEEL_UP && glutGetModifiers()==GLUT_ACTIVE_CTRL) {
}else if (button == GLUT_WHEEL_DOWN)
glutPostRedisplay();
}
*/
int main (int argc, char** argv) {
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
glutInitWindowPosition (50, 50);
glutInitWindowSize (winWidth, winHeight);
glutCreateWindow ("Bezier Curve");
init ( );
glutDisplayFunc (displayFcn);
glutReshapeFunc (winReshapeFcn);
glutMouseFunc(MouseCallback);
glutMotionFunc(MotionCallback);
glutMainLoop ( );
}

Answer 1

Try this:
#include <GL/glut.h>
#include <cmath>
// Compute binomial coefficients C for given value of n.
void binomialCoeffs
(
GLint n,
GLint* C
)
{
for (GLint k = 0; k <= n; k++)
{
// Compute n!/(k!(n - k)!).
C [k] = 1;
for (GLint j = n; j >= k + 1; j--)
C [k] *= j;
for (GLint j = n - k; j >= 2; j--)
C [k] /= j;
}
}
struct wcPt3D
{
GLfloat x, y, z;
};
void computeBezPt
(
GLfloat t,
wcPt3D* bezPt,
GLint nCtrlPts,
wcPt3D* ctrlPts,
GLint* C
)
{
GLint n = nCtrlPts - 1;
GLfloat bezBlendFcn;
bezPt->x = bezPt->y = bezPt->z = 0.0;
// Compute blending functions and blend control points.
for (GLint k = 0; k < nCtrlPts; k++)
{
bezBlendFcn = C [k] * pow (t, k) * pow (1 - t, n - k);
bezPt->x += ctrlPts [k].x * bezBlendFcn;
bezPt->y += ctrlPts [k].y * bezBlendFcn;
bezPt->z += ctrlPts [k].z * bezBlendFcn;
}
}
void bezier
(
wcPt3D* ctrlPts,
GLint nCtrlPts,
GLint nBezCurvePts
)
{
// Allocate space for binomial coefficients
GLint* C = new GLint [nCtrlPts];
binomialCoeffs (nCtrlPts - 1, C);
glBegin (GL_POINTS);
for (int i = 0; i <= nBezCurvePts; i++)
{
GLfloat t = GLfloat (i) / GLfloat (nBezCurvePts);
wcPt3D bezCurvePt;
computeBezPt (t, &bezCurvePt, nCtrlPts, ctrlPts, C);
glVertex2f (bezCurvePt.x, bezCurvePt.y);
}
glEnd();
delete [ ] C;
}
int btn;
int startMouseX = 0;
int startMouseY = 0;
int startTransX = 0;
int startTransY = 0;
int curTransX = 0;
int curTransY = 0;
void MouseCallback(int button, int state, int x, int y)
{
btn = button;
if( button == GLUT_LEFT_BUTTON && state == GLUT_DOWN )
{
startMouseX = x;
startMouseY = glutGet( GLUT_WINDOW_HEIGHT ) - y;
startTransX = curTransX;
startTransY = curTransY;
}
glutPostRedisplay();
}
void MotionCallback(int x, int y)
{
int curMouseX = x;
int curMouseY = glutGet( GLUT_WINDOW_HEIGHT ) - y;
if ( btn == GLUT_LEFT_BUTTON )
{
curTransX = startTransX + ( curMouseX - startMouseX );
curTransY = startTransY + ( curMouseY - startMouseY );
}
glutPostRedisplay();
}
// Set size of world-coordinate clipping window.
GLfloat xwcMin = -50.0, xwcMax = 50.0;
GLfloat ywcMin = -50.0, ywcMax = 50.0;
void displayFcn ()
{
// Clear display window.
glClearColor (1.0, 1.0, 1.0, 0.0);
glClear (GL_COLOR_BUFFER_BIT);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ( );
double w = glutGet( GLUT_WINDOW_WIDTH );
double h = glutGet( GLUT_WINDOW_HEIGHT );
glTranslatef( curTransX / w * 2, curTransY / h * 2, 0 );
gluOrtho2D (xwcMin, xwcMax, ywcMin, ywcMax);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
// Set example number of control points and number of
// curve positions to be plotted along the Bezier curve.
GLint nCtrlPts = 4, nBezCurvePts = 1000;
wcPt3D ctrlPts [4] =
{
{-40.0, -40.0, 0.0},
{-10.0, 200.0, 0.0},
{10.0, -200.0, 0.0},
{40.0, 40.0, 0.0}
};
// Set point color to red.
glPointSize (4);
glColor3f (1.0, 0.0, 0.0);
bezier (ctrlPts, nCtrlPts, nBezCurvePts);
glutSwapBuffers();
}
int main (int argc, char** argv)
{
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
glutInitWindowPosition (50, 50);
glutInitWindowSize (600, 600);
glutCreateWindow ("Bezier Curve");
glutDisplayFunc (displayFcn);
glutMouseFunc(MouseCallback);
glutMotionFunc(MotionCallback);
glutMainLoop ( );
}
Adapted from my answer here.
EDIT: Minimal(-ish) difference version:
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>
#if !defined(GLUT_WHEEL_UP)
# define GLUT_WHEEL_UP
# define GLUT_WHEEL_DOWN 4
#endif
/* Set initial size of the display window. */
GLsizei winWidth = 600, winHeight = 600;
/* Set size of world-coordinate clipping window. */
GLfloat xwcMin = -50.0, xwcMax = 50.0;
GLfloat ywcMin = -50.0, ywcMax = 50.0;
class wcPt3D {
public:
GLfloat x, y, z;
};
void init (void) {
/* Set color of display window to white. */
glClearColor (1.0, 1.0, 1.0, 0.0);
}
void plotPoint (wcPt3D bezCurvePt) {
glBegin (GL_POINTS);
glVertex2f (bezCurvePt.x, bezCurvePt.y);
glEnd ( );
}
/* Compute binomial coefficients C for given value of n. */
void binomialCoeffs (GLint n, GLint * C) {
GLint k, j;
for (k = 0; k <= n; k++) {
/* Compute n!/(k!(n - k)!). */
C [k] = 1;
for (j = n; j >= k + 1; j--)
C [k] *= j;
for (j = n - k; j >= 2; j--)
C [k] /= j;
}
}
void computeBezPt (GLfloat t, wcPt3D * bezPt, GLint nCtrlPts,
wcPt3D * ctrlPts, GLint * C) {
GLint k, n = nCtrlPts - 1;
GLfloat bezBlendFcn;
bezPt->x = bezPt->y = bezPt->z = 0.0;
/* Compute blending functions and blend control points. */
for (k = 0; k < nCtrlPts; k++) {
bezBlendFcn = C [k] * pow (t, k) * pow (1 - t, n - k);
bezPt->x += ctrlPts [k].x * bezBlendFcn;
bezPt->y += ctrlPts [k].y * bezBlendFcn;
bezPt->z += ctrlPts [k].z * bezBlendFcn;
}
}
void bezier (wcPt3D * ctrlPts, GLint nCtrlPts, GLint nBezCurvePts) {
wcPt3D bezCurvePt;
GLfloat t;
GLint *C;
/* Allocate space for binomial coefficients */
C = new GLint [nCtrlPts];
binomialCoeffs (nCtrlPts - 1, C);
for (int i = 0; i <= nBezCurvePts; i++) {
t = GLfloat (i) / GLfloat (nBezCurvePts);
computeBezPt (t, &bezCurvePt, nCtrlPts, ctrlPts, C);
plotPoint (bezCurvePt);
}
delete [ ] C;
}
int curTransX = 0;
int curTransY = 0;
void displayFcn (void) {
glClear (GL_COLOR_BUFFER_BIT); // Clear display window.
glMatrixMode (GL_PROJECTION);
glLoadIdentity ( );
double w = glutGet( GLUT_WINDOW_WIDTH );
double h = glutGet( GLUT_WINDOW_HEIGHT );
glTranslatef( curTransX / w * 2, curTransY / h * 2, 0 );
gluOrtho2D (xwcMin, xwcMax, ywcMin, ywcMax);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
/* Set example number of control points and number of
* curve positions to be plotted along the Bezier curve.
*/ GLint nCtrlPts = 4, nBezCurvePts = 1000;
wcPt3D ctrlPts [4] = { {-40.0, -40.0, 0.0}, {-10.0, 200.0, 0.0},
{10.0, -200.0, 0.0}, {40.0, 40.0, 0.0} };
glPointSize (4);
glColor3f (1.0, 0.0, 0.0); // Set point color to red.
bezier (ctrlPts, nCtrlPts, nBezCurvePts);
glutSwapBuffers();
}
int btn;
int startMouseX = 0;
int startMouseY = 0;
int startTransX = 0;
int startTransY = 0;
void MouseCallback(int button, int state, int x, int y) {
btn = button;
if( button == GLUT_LEFT_BUTTON && state == GLUT_DOWN )
{
startMouseX = x;
startMouseY = glutGet( GLUT_WINDOW_HEIGHT ) - y;
startTransX = curTransX;
startTransY = curTransY;
}
glutPostRedisplay();
}
void MotionCallback(int x, int y) {
int curMouseX = x;
int curMouseY = glutGet( GLUT_WINDOW_HEIGHT ) - y;
if ( btn == GLUT_LEFT_BUTTON )
{
curTransX = startTransX + ( curMouseX - startMouseX );
curTransY = startTransY + ( curMouseY - startMouseY );
}
glutPostRedisplay();
}
/*
void MouseCallback(int button, int state, int x, int y) {
if (button == GLUT_WHEEL_UP && glutGetModifiers()==GLUT_ACTIVE_CTRL) {
}else if (button == GLUT_WHEEL_DOWN)
glutPostRedisplay();
}
*/
int main (int argc, char** argv) {
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
glutInitWindowPosition (50, 50);
glutInitWindowSize (winWidth, winHeight);
glutCreateWindow ("Bezier Curve");
init ( );
glutDisplayFunc (displayFcn);
glutMouseFunc(MouseCallback);
glutMotionFunc(MotionCallback);
glutMainLoop ( );
}