如何在C ++中使用浮点值在C ++中绘制Bezier曲线

Question

我正在尝试使用浮点值在OpenGL中绘制Bezier曲线。 我尝试使用许多不同的代码示例。 我下面的当前代码可以运行，但不会在屏幕上显示曲线。 绘制Bezier曲线的常用方法是使用整数值，这意味着使用GLUORTHO2D()函数绘制曲线。 但是我想使用浮点值绘制一条曲线。 例如x range(-1,1)和y range(-1,1) 。

如if x=(500)则将其视为(-1 to 1)而if y=(800)则将其视为(-1,1) 。

我已经尝试使用整数值，它为我工作。 我的代码使用整数值如下：

#include <GL/glut.h>
#include <math.h>
#include <stdio.h>
#define CTRL_COUNT 100
int ctrlPointsCount;
int ctrlPointsX[CTRL_COUNT], ctrlPointsY[CTRL_COUNT];
int X1[3]={20,25,20}, Y1[3]={5,24,38};  //first point(x1[0],y1[0])    second(x1[1],y1[1]) third(x1[2],y1[2])

void myInit()
{
glClearColor(0.0,0.0,0.0,0.0);
glColor3f(1.0,0.0,0.0);
glPointSize(8.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0,128.0,0.0,96.0);
}
//p(t)=(1-t)^3*p0+3t(1-t)^2*p1+3t^2(1-t)p2+t^3p3
float getNextBezierPointX(float t)
{
float x=0.0;

for(int i=0; i<ctrlPointsCount; i++)
{
int c;
if(i==0 || i==ctrlPointsCount-1)
    c = 1;
else
{
    c = ctrlPointsCount-1;
}
x +=  c * pow(t, i) * pow(1-t, ctrlPointsCount-1-i) * ctrlPointsX[i];
}


return x;
}

float getNextBezierPointY(float t)
{
float y=0.0;

for(int i=0; i<ctrlPointsCount; i++)
{
int c;
if(i==0 || i==ctrlPointsCount-1)
    c = 1;
else
{
    c = ctrlPointsCount-1;
}
y +=  c * pow(t, i) * pow(1-t, ctrlPointsCount-1-i) * ctrlPointsY[i];
}



return y;
}
void drawline()
{
// draw control points using red color
for(int i=0; i < 3; i++)
{
glBegin(GL_POINTS);
glVertex2i(ctrlPointsX[i], ctrlPointsY[i]);
glEnd();
glFlush();
}
// draw bezier curve using control poitns by calculating next points using          cubic bezier curve formula
float oldX=ctrlPointsX[0], oldY=ctrlPointsY[0];
for(double t = 0.0;t <= 1.0; t += 0.01) {

float x = getNextBezierPointX(t);
float y = getNextBezierPointY(t);
//glColor3f(1.0,t,1.0);
glColor3f(1.0,1.0,1.0);
glBegin(GL_LINES);
glVertex2f(oldX, oldY);
glVertex2f(x, y);
glEnd();
glFlush();

oldX = x;
oldY = y;
}
}

void myDisplay()
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0,0.0,0.0);
ctrlPointsCount=3;
for(int i=0;i<3;i++)
{
ctrlPointsX[i] = X1[i];
ctrlPointsY[i] = Y1[i];
}
drawline();


glFlush();
}


int main(int argc, char *argv[])
{

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowSize(640,480);
glutInitWindowPosition(100,150);
glutCreateWindow("Bezier Curve");
glutDisplayFunc(myDisplay);
myInit();
glutMainLoop();
return 0;
}

但是当我尝试使用浮点值时，它对我不起作用。 它不在屏幕上显示曲线。 我的代码使用浮点值如下：

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>
using namespace std;
#define CTRL_COUNT 100

int ctrlPointsCount;
int ctrlPointsX[CTRL_COUNT], ctrlPointsY[CTRL_COUNT];
double X1[3] = { 0.26015037593985, 0.43609022556391, 0.6 }, Y1[3] = {           0.946875, 0.884375, 0.946875 };
//Initializes 3D rendering
void initRendering() {
glEnable(GL_DEPTH_TEST); 
}
float getNextBezierPointX(float t)
{
float x = 0.0;

for (int i = 0; i<ctrlPointsCount; i++)
{
int c;
if (i == 0 || i == ctrlPointsCount - 1)
    c = 1;
else
{
    c = ctrlPointsCount - 1;
}
x += c * pow(t, i) * pow(1 - t, ctrlPointsCount - 1 - i) *        ctrlPointsX[i];
}

return x;
}
float getNextBezierPointY(float t)
{
float y = 0.0;
for (int i = 0; i<ctrlPointsCount; i++)
{
int c;
if (i == 0 || i == ctrlPointsCount - 1)
    c = 1;
else
{
    c = ctrlPointsCount - 1;
}
y += c * pow(t, i) * pow(1 - t, ctrlPointsCount - 1 - i) *        ctrlPointsY[i];
}
return y;
}
void drawline()
{
// draw control points using red color
for (int i = 0; i < 3; i++)
{
glBegin(GL_POINTS);
glVertex2i(ctrlPointsX[i], ctrlPointsY[i]);
glEnd();
glFlush();
}
// draw bezier curve using control poitns by calculating next points using           cubic bezier curve formula
float oldX = ctrlPointsX[0], oldY = ctrlPointsY[0];
for (double t = 0.0; t <= 1.0; t += 0.01)
        {
float x = getNextBezierPointX(t);
float y = getNextBezierPointY(t);
//glColor3f(1.0,t,1.0);
glColor3f(1.0, 1.0, 1.0);
glBegin(GL_LINES);
glVertex2f(oldX, oldY);
glVertex2f(x, y);
glEnd();
glFlush();
oldX = x;
oldY = y;
}
}
//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 = 0.0;
float _cameraAngle = 0.0;
float _ang_tri = 0.0;
//Draws the 3D scene
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity(); //Reset the drawing perspective
ctrlPointsCount = 3;
for (int i = 0; i<3; i++)
{
ctrlPointsX[i] = X1[i];
ctrlPointsY[i] = Y1[i];
}
drawline();
glutSwapBuffers();
}
void update(int value) {
_angle += 2.0f;
if (_angle > 360) {
_angle -= 360;
}
_ang_tri += 2.0f;
if (_ang_tri > 360) {
_ang_tri -= 360;
}
glutPostRedisplay(); //Tell GLUT that the display has changed
//Tell GLUT to call update again in 25 milliseconds
glutTimerFunc(25, update, 0);
}
int main(int argc, char** argv) {
//Initialize GLUT

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(1331, 641);
glutInitWindowPosition(0, 0);

//Create the window
glutCreateWindow("Our cg project");
initRendering();

//Set handler functions
glutDisplayFunc(drawScene);

glutReshapeFunc(handleResize);

glutTimerFunc(25, update, 0); //Add a timer

glClearColor(0.0, 0.7, 1.5,0.0);

glutMainLoop();
return 0;
}

Answer 1

问题是这样的：

int ctrlPointsX[CTRL_COUNT], ctrlPointsY[CTRL_COUNT];
double X1[3] = { 0.26015037593985, 0.43609022556391, 0.6 }, Y1[3] = {0.946875, 0.884375, 0.946875 };

for (int i = 0; i<3; i++)
{
ctrlPointsX[i] = X1[i];
ctrlPointsY[i] = Y1[i];
}

ctrlPointsX和ctrlPointsY只能保存整数值。 因此，当您执行ctrlPointsX[i] = X1[i]和ctrlPointsY[i] = Y1[i]您会将浮点数转换为整数，从而将其四舍五入。 因此，您的所有controlPoints将为0。

您还必须将controlPoints数组声明为double类型：

double ctrlPointsX[CTRL_COUNT], ctrlPointsY[CTRL_COUNT];
double X1[3] = { 0.26015037593985, 0.43609022556391, 0.6 }, Y1[3] = {0.946875, 0.884375, 0.946875 };

这应该可以解决您的问题。