OpenGL - 旋转“曲线”关于 Y 轴
根据我在 Math Stackexchange 上的问题:
我我正在为我的 3D 图形课程做一个项目。该项目是用 C++ 和 OpenGL / Glut 构建的。基本上,我创建一个水平矩形窗口,细分为两个正方形。在左侧,我有一个二维坐标平面,它允许用户指向并单击并定义轮廓“曲线”。然后我需要将该曲线绕 Y 轴缠绕 n 次。
那么,有人能指导我如何使用三角学来计算连续点的 X 和 Z 值吗?例如,如果用户单击并创建点:
(1, 1, 0)
并且他们的扫描分辨率 (n) 设置为 10,那么我需要每 36 (360/10) 度重绘该点Y 轴。
我假设三角学在这里对我有帮助是正确的吗?如果是这样,有人可以告诉我如何计算 3D 空间中平移点的位置吗?自从我学习三角函数以来已经有一段时间了,我不相信我们曾经离开过二维空间。
编辑:我尝试使用:
x'=xcos(theta)-zsin(theta)
y'=y
z'=xsin(theta)+zcos(theta)
,根据我对 AMPerrine 的 答案,我认为它没有像我希望的那样工作:
// this is in a loop
// setup the new angle
double angle = i>0 ? (360/sweepResolutionMod)*i : 0;
angle = angle * (M_PI/180);
// for each point...
for( int i=0; i<clickedPoints.size(); i++ )
{
// initial point, normalized
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// log the initial point
cout << "(" << tempX << ", " << tempY << ", 0.0) by " << angle << " radians = ";
// generate the new point
GLfloat newX = (tempX * cos(angle)) - (tempZ * sin(angle));
GLfloat newY = tempY;
GLfloat newZ = (tempX * sin(angle)) - (tempZ * cos(angle));
// log the new point
cout << "(" << newX << ", " << newY << ", " << newZ << ")\n";
// render the new point
glVertex3d(newX, newY, newZ);
}
这不会产生屏幕输出,但会产生控制台输出:
(0.048, -0.296, 0.0) by 0 radians = (0.048, -0.296, 0)
(0.376, -0.508, 0.0) by 0 radians = (0.376, -0.508, 0)
(0.72, -0.204, 0.0) by 0 radians = (0.72, -0.204, 0)
(0.652, 0.176, 0.0) by 0 radians = (0.652, 0.176, 0)
(0.368, 0.504, 0.0) by 0 radians = (0.368, 0.504, 0)
(0.048, -0.296, 0.0) by 0.628319 radians = (0.0388328, -0.296, 0.0282137)
(0.376, -0.508, 0.0) by 0.628319 radians = (0.30419, -0.508, 0.221007)
(0.72, -0.204, 0.0) by 0.628319 radians = (0.582492, -0.204, 0.423205)
(0.652, 0.176, 0.0) by 0.628319 radians = (0.527479, 0.176, 0.383236)
(0.368, 0.504, 0.0) by 0.628319 radians = (0.297718, 0.504, 0.216305)
(0.048, -0.296, 0.0) by 1.25664 radians = (0.0148328, -0.296, 0.0456507)
(0.376, -0.508, 0.0) by 1.25664 radians = (0.11619, -0.508, 0.357597)
(0.72, -0.204, 0.0) by 1.25664 radians = (0.222492, -0.204, 0.684761)
(0.652, 0.176, 0.0) by 1.25664 radians = (0.201479, 0.176, 0.620089)
(0.368, 0.504, 0.0) by 1.25664 radians = (0.113718, 0.504, 0.349989)
...
(0.048, -0.296, 0.0) by 6.28319 radians = (0.048, -0.296, -1.17566e-17)
(0.376, -0.508, 0.0) by 6.28319 radians = (0.376, -0.508, -9.20934e-17)
(0.72, -0.204, 0.0) by 6.28319 radians = (0.72, -0.204, -1.76349e-16)
(0.652, 0.176, 0.0) by 6.28319 radians = (0.652, 0.176, -1.59694e-16)
(0.368, 0.504, 0.0) by 6.28319 radians = (0.368, 0.504, -9.0134e-17)
我不确定到底发生了什么在这里,但我在试图解决这个问题时经历了一段糟糕的时光,所以请不要认为我是在试图获得双重声誉或其他什么,我只是真的陷入了困境。
编辑 2:这是我的透视子视图的整个显示例程:
void displayPersp(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
gluLookAt (-2.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
// draw the axis
glBegin(GL_LINES);
// x
glVertex3f(500.0, 0.0, 0.0);
glVertex3f(-500.0, 0.0, 0.0);
// y
glVertex3f(0.0, -500.0, 0.0);
glVertex3f(0.0, 500.0, 0.0);
// z
glVertex3f(0.0, 0.0, -500.0);
glVertex3f(0.0, 0.0, 500.0);
glEnd();
cout << endl;
// loop as many number of times as we are going to draw the points around the Y-Axis
for( int i=0; i<=sweepResolutionMod; i++ )
{
cout << endl;
// setup the new angle
double angle = i>0 ? (360/sweepResolutionMod)*i : 0;
angle = angle * (M_PI/180);
// for each point...
for( int i=0; i<clickedPoints.size(); i++ )
{
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
cout << "(" << tempX << ", " << tempY << ", 0.0) by " << angle << " degrees = ";
GLfloat newX = (tempX * cos(angle)) - (tempZ * sin(angle));
GLfloat newY = tempY;
GLfloat newZ = (tempX * sin(angle)) - (tempZ * cos(angle));
cout << "(" << newX << ", " << newY << ", " << newZ << ")\n";
glVertex3d(newX, newY, newZ);
}
// the following was my old solution, using OpenGL's rotate(), but that
// didn't allow me to get back the new point's coordinates.
/*
glRotatef(angle, 0.0, 1.0, 0.0);
// draw a line?
if( clickedPoints.size() > 1 )
{
glBegin(GL_LINE_STRIP);
for(int i=0; i<clickedPoints.size(); i++ )
{
glVertex3f((clickedPoints[i].x-250)/250, (clickedPoints[i].y-250)/250, 0.0);
}
glEnd();
}
// everyone gets points
glBegin(GL_POINTS);
for(int i=0; i<clickedPoints.size(); i++ )
{
glVertex3f((clickedPoints[i].x-250)/250, (clickedPoints[i].y-250)/250, 0.0);
}
glEnd();
*/
}
glutSwapBuffers();
}
编辑3:这是一个糟糕的插图,说明了我需要做什么。 我试图获取的是右侧子视图中的绿色“水平线”(这是使用上面注释掉的 glRotatef() 代码):
我知道视角似乎不对,但 sstatic.net/Qcpno.jpg" alt="Pic">
最终编辑(为了后代!):
这是我在与老师讨论了一些线性代数之后最终得到的结果 大学:
void displayPersp(void)
{
glClear(GL_COLOR_BUFFER_BIT);
gluLookAt (-2.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
// draw the axis
glBegin(GL_LINES);
// x
glVertex3f(500.0, 0.0, 0.0);
glVertex3f(-500.0, 0.0, 0.0);
// y
glVertex3f(0.0, -500.0, 0.0);
glVertex3f(0.0, 500.0, 0.0);
// z
glVertex3f(0.0, 0.0, -500.0);
glVertex3f(0.0, 0.0, 500.0);
glEnd();
cout << endl;
double previousTheta = 0.0;
for( int i=0; i<=sweepResolutionMod; i++ )
{
double theta = i>0 ? (360/sweepResolutionMod)*i : 0;
theta = theta * (M_PI/180);
if( clickedPoints.size() > 1 )
{
// the 'vertical' piece
glBegin(GL_LINE_STRIP);
for(int i=0; i<clickedPoints.size(); i++ )
{
// normalize
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// new points
GLfloat newX = ( tempX * cos(theta) ) + ( tempZ * sin(theta) );
GLfloat newY = tempY;
GLfloat newZ = ( tempZ * cos(theta) ) - ( tempX * sin(theta) );
glVertex3f(newX, newY, newZ);
}
glEnd();
// the 'horizontal' piece
if( previousTheta != theta )
{
glBegin(GL_LINES);
for(int i=0; i<clickedPoints.size(); i++ )
{
// normalize
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// new points
GLfloat newX = ( tempX * cos(theta) ) + ( tempZ * sin(theta) );
GLfloat newY = tempY;
GLfloat newZ = ( tempZ * cos(theta) ) - ( tempX * sin(theta) );
// previous points
GLfloat previousX = ( tempX * cos(previousTheta) ) + ( tempZ * sin(previousTheta) );
GLfloat previousY = tempY;
GLfloat previousZ = ( tempZ * cos(previousTheta) ) - ( tempX * sin(previousTheta) );
// horizontal component
glVertex3f(newX, newY, newZ);
glVertex3f(previousX, previousY, previousZ);
}
glEnd();
}
}
previousTheta = theta;
}
glutSwapBuffers();
}
As per my question on Math Stackexchange:
I am working on a project for my 3D Graphics class. The project is built with C++ and OpenGL / Glut. Basically, I create a horizontal rectangle window, subdivided into two squares. On the left, I have a two dimensional coordinate plane, which allows the users to point and click and define a profile 'curve'. I then need to wrap this curve around the Y-axis n number of times.
So, would anyone be able to guide me as to how I would use Trigonometry to calculate the X and Z values of the successive points? If for example, a user clicks and creates the point:
(1, 1, 0)
And their sweep resolution (n) is set to, say, 10, then I need to redraw that point every 36 (360/10) degrees around the Y-axis.
Am I correct in assuming that Trigonometry will help me here? If so, can someone please enlighten me a bit as to how to calculate the location of a translated point in 3D space? It's been a while since I took Trig, and I don't believe we ever left 2D space.
EDIT: I attempted to use:
x'=xcos(theta)-zsin(theta)
y'=y
z'=xsin(theta)+zcos(theta)
, as per my understanding of AMPerrine's answer, and I don't think it worked as I'd hoped:
// this is in a loop
// setup the new angle
double angle = i>0 ? (360/sweepResolutionMod)*i : 0;
angle = angle * (M_PI/180);
// for each point...
for( int i=0; i<clickedPoints.size(); i++ )
{
// initial point, normalized
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// log the initial point
cout << "(" << tempX << ", " << tempY << ", 0.0) by " << angle << " radians = ";
// generate the new point
GLfloat newX = (tempX * cos(angle)) - (tempZ * sin(angle));
GLfloat newY = tempY;
GLfloat newZ = (tempX * sin(angle)) - (tempZ * cos(angle));
// log the new point
cout << "(" << newX << ", " << newY << ", " << newZ << ")\n";
// render the new point
glVertex3d(newX, newY, newZ);
}
This produces no screen output, but console output of:
(0.048, -0.296, 0.0) by 0 radians = (0.048, -0.296, 0)
(0.376, -0.508, 0.0) by 0 radians = (0.376, -0.508, 0)
(0.72, -0.204, 0.0) by 0 radians = (0.72, -0.204, 0)
(0.652, 0.176, 0.0) by 0 radians = (0.652, 0.176, 0)
(0.368, 0.504, 0.0) by 0 radians = (0.368, 0.504, 0)
(0.048, -0.296, 0.0) by 0.628319 radians = (0.0388328, -0.296, 0.0282137)
(0.376, -0.508, 0.0) by 0.628319 radians = (0.30419, -0.508, 0.221007)
(0.72, -0.204, 0.0) by 0.628319 radians = (0.582492, -0.204, 0.423205)
(0.652, 0.176, 0.0) by 0.628319 radians = (0.527479, 0.176, 0.383236)
(0.368, 0.504, 0.0) by 0.628319 radians = (0.297718, 0.504, 0.216305)
(0.048, -0.296, 0.0) by 1.25664 radians = (0.0148328, -0.296, 0.0456507)
(0.376, -0.508, 0.0) by 1.25664 radians = (0.11619, -0.508, 0.357597)
(0.72, -0.204, 0.0) by 1.25664 radians = (0.222492, -0.204, 0.684761)
(0.652, 0.176, 0.0) by 1.25664 radians = (0.201479, 0.176, 0.620089)
(0.368, 0.504, 0.0) by 1.25664 radians = (0.113718, 0.504, 0.349989)
...
(0.048, -0.296, 0.0) by 6.28319 radians = (0.048, -0.296, -1.17566e-17)
(0.376, -0.508, 0.0) by 6.28319 radians = (0.376, -0.508, -9.20934e-17)
(0.72, -0.204, 0.0) by 6.28319 radians = (0.72, -0.204, -1.76349e-16)
(0.652, 0.176, 0.0) by 6.28319 radians = (0.652, 0.176, -1.59694e-16)
(0.368, 0.504, 0.0) by 6.28319 radians = (0.368, 0.504, -9.0134e-17)
I'm not sure what exactly is going on here, but I'm having a terrible time trying to figure it out, so please don't think I'm trying to get double reputation or anything, I'm just really stuck.
EDIT 2: Here is my whole display routine for my perspective subview:
void displayPersp(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
gluLookAt (-2.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
// draw the axis
glBegin(GL_LINES);
// x
glVertex3f(500.0, 0.0, 0.0);
glVertex3f(-500.0, 0.0, 0.0);
// y
glVertex3f(0.0, -500.0, 0.0);
glVertex3f(0.0, 500.0, 0.0);
// z
glVertex3f(0.0, 0.0, -500.0);
glVertex3f(0.0, 0.0, 500.0);
glEnd();
cout << endl;
// loop as many number of times as we are going to draw the points around the Y-Axis
for( int i=0; i<=sweepResolutionMod; i++ )
{
cout << endl;
// setup the new angle
double angle = i>0 ? (360/sweepResolutionMod)*i : 0;
angle = angle * (M_PI/180);
// for each point...
for( int i=0; i<clickedPoints.size(); i++ )
{
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
cout << "(" << tempX << ", " << tempY << ", 0.0) by " << angle << " degrees = ";
GLfloat newX = (tempX * cos(angle)) - (tempZ * sin(angle));
GLfloat newY = tempY;
GLfloat newZ = (tempX * sin(angle)) - (tempZ * cos(angle));
cout << "(" << newX << ", " << newY << ", " << newZ << ")\n";
glVertex3d(newX, newY, newZ);
}
// the following was my old solution, using OpenGL's rotate(), but that
// didn't allow me to get back the new point's coordinates.
/*
glRotatef(angle, 0.0, 1.0, 0.0);
// draw a line?
if( clickedPoints.size() > 1 )
{
glBegin(GL_LINE_STRIP);
for(int i=0; i<clickedPoints.size(); i++ )
{
glVertex3f((clickedPoints[i].x-250)/250, (clickedPoints[i].y-250)/250, 0.0);
}
glEnd();
}
// everyone gets points
glBegin(GL_POINTS);
for(int i=0; i<clickedPoints.size(); i++ )
{
glVertex3f((clickedPoints[i].x-250)/250, (clickedPoints[i].y-250)/250, 0.0);
}
glEnd();
*/
}
glutSwapBuffers();
}
EDIT 3: Here is a terrible illustration that illustrates what I need to do. I know the perspective seems off, but what I'm attempting to acquire is the green 'horizontals' in the right subview (this is using the commented out glRotatef() code above):
FINAL EDIT (for future generations!):
Here is what I finally got working, after discussing some linear algebra with a teacher at college:
void displayPersp(void)
{
glClear(GL_COLOR_BUFFER_BIT);
gluLookAt (-2.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
// draw the axis
glBegin(GL_LINES);
// x
glVertex3f(500.0, 0.0, 0.0);
glVertex3f(-500.0, 0.0, 0.0);
// y
glVertex3f(0.0, -500.0, 0.0);
glVertex3f(0.0, 500.0, 0.0);
// z
glVertex3f(0.0, 0.0, -500.0);
glVertex3f(0.0, 0.0, 500.0);
glEnd();
cout << endl;
double previousTheta = 0.0;
for( int i=0; i<=sweepResolutionMod; i++ )
{
double theta = i>0 ? (360/sweepResolutionMod)*i : 0;
theta = theta * (M_PI/180);
if( clickedPoints.size() > 1 )
{
// the 'vertical' piece
glBegin(GL_LINE_STRIP);
for(int i=0; i<clickedPoints.size(); i++ )
{
// normalize
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// new points
GLfloat newX = ( tempX * cos(theta) ) + ( tempZ * sin(theta) );
GLfloat newY = tempY;
GLfloat newZ = ( tempZ * cos(theta) ) - ( tempX * sin(theta) );
glVertex3f(newX, newY, newZ);
}
glEnd();
// the 'horizontal' piece
if( previousTheta != theta )
{
glBegin(GL_LINES);
for(int i=0; i<clickedPoints.size(); i++ )
{
// normalize
GLfloat tempX = (clickedPoints[i].x-250)/250;
GLfloat tempY = (clickedPoints[i].y-250)/250;
GLfloat tempZ = 0.0;
// new points
GLfloat newX = ( tempX * cos(theta) ) + ( tempZ * sin(theta) );
GLfloat newY = tempY;
GLfloat newZ = ( tempZ * cos(theta) ) - ( tempX * sin(theta) );
// previous points
GLfloat previousX = ( tempX * cos(previousTheta) ) + ( tempZ * sin(previousTheta) );
GLfloat previousY = tempY;
GLfloat previousZ = ( tempZ * cos(previousTheta) ) - ( tempX * sin(previousTheta) );
// horizontal component
glVertex3f(newX, newY, newZ);
glVertex3f(previousX, previousY, previousZ);
}
glEnd();
}
}
previousTheta = theta;
}
glutSwapBuffers();
}
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评论(3)
看起来您正在尝试构建旋转表面/旋转固体/"车床对象" 。
一个工作示例:
Looks like you're trying to construct a surface of revolution/solid of revolution/"lathe object".
A working example:
编辑2:好的,我看到你遇到的问题了——这是我忘记的一个限制(所以我之前发布的代码是完全错误的,根本不起作用)。问题是你不允许在
glBegin
/glEnd
对之间调用glRotate
—— 如果你这样做,它会设置一个错误标志,并且不会再进行绘制。这确实意味着您几乎必须自己处理轮换。幸运的是,这比您尝试的要简单一些:
按原样,此代码使用沿 Z 轴的 -1.0 作为旋转中心。显然,您可以将其移动到您想要的位置,但剪切平截头体之外的任何内容显然都不会显示。
另请注意,要获得线框,您必须分别绘制“垂直”线和“水平”线,因此代码将如下所示:
Edit 2: Okay, I see the problem you're running into -- it's a limitation I'd forgotten about (so the code I'd posted previously was dead wrong and wouldn't work at all). The problem is that you're not allowed to call
glRotate
between aglBegin
/glEnd
pair -- if you do, it'll set an error flag, and no more drawing will be done.That does mean you pretty much have to handle the rotation yourself. Fortunately, that's a bit simpler than you've tried to make it:
As-is, this code uses -1.0 along the Z axis as the center of rotation. You can obviously move that where you wish, though anything outside your clipping frustum obviously won't display.
Also note that to get a wireframe, you'll have to draw both your "vertical", and your "horizontal" lines separately, so the code will look something like this:
三角函数以弧度为单位,而不是度数。
我还怀疑您的视口设置不正确,这解释了为什么您在屏幕上看不到任何内容。通常,当我认为某些东西没有渲染时,它通常是渲染的,但是,我没有正确配置相机、灯光和其他东西。
The trig functions take angles in radians, not degrees.
I also suspect that your viewport isn't setup properly, which explains why you can't see anything on the screen. Typically when I think stuff isn't rendering, it usually is, however, I haven't configured the camera, lighting and other stuff correctly.