无法在鼠标单击 OpenGL 时围绕其自身中心旋转对象
Can't rotate object around its own center on mouse click OpenGL
我成功地旋转了我的对象,但我需要右键单击该对象以停止其旋转。我不知道如何使对象绕其中心旋转然后停止,我将附上代码以查看此形状到底发生了什么。我认为问题出在 spinDisplay()
函数上……问题是我需要在单击鼠标左键时围绕它的中心旋转,而在单击鼠标右键时我应该更改对象的颜色…… .
#include <stdlib.h>
#include <math.h>
#include "dependente\freeglut\freeglut.h"
#include "dependente\glfw\glfw3.h"
#include <stdio.h> //incluziuni librarii
float ORG[3] = { 0,0,0 };
static GLfloat spin = 0.0;
GLfloat viewangle = 0, tippangle = 0, traj[120][3]; //variabila pentru unghi camera
GLfloat d[3] = { 0.1, 0.1, 0.1 }; //vector directie
GLfloat xAngle = 0.0, yAngle = 0.0, zAngle = 0.0;
bool draw_triangle = false; //variabila desenat figuri
bool draw_square = false;
bool draw_decagon = false;
void Triangle(void) //draw the triangle shape
{
glBegin(GL_TRIANGLE_FAN);//triangles have a common vertex, which is the central vertex
glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(0.0f, 1.0f, 0.0f); //V0(red)
glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); //V1(green)
glColor3f(0.0f, 0.0f, 1.0f); glVertex3f(1.0f, -1.0f, 1.0f); //V2(blue)
glEnd();
}
void Square(void) {
glBegin(GL_QUADS);
glVertex2f(-1.0f, 1.0f); // top left
glVertex2f(1.0f, 1.0f); // top right
glVertex2f(1.0f, -1.0f); // bottom right
glVertex2f(-1.0f, -1.0f); // bottom left
glEnd();
}
void Decagon(void) //draw the decagon shape
{
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.72f,0.8f, 0.0f); //a1
glVertex3f(0.52f, 0.8f,0.0f); //z
glVertex3f(0.35f, 0.64f, 0.0f); //b1
glVertex3f(0.3f, 0.48f, 0.0f); //d1
glVertex3f(0.35f, 0.3f, 0.0f); //e1
glVertex3f(0.52f, 0.16f, 0.0f); //l1
glVertex3f(0.72f, 0.16f, 0.0f); //m1
glVertex3f(0.9f, 0.3f, 0.0f); //o1
glVertex3f(0.95f, 0.48f, 0.0f); //p1
glVertex3f(0.9f, 0.64f, 0.0f); //c1
glScalef(10, 10, 10);
glTranslatef(1, 2, 3);
glEnd();
}
void Keyboard(unsigned char key, int x, int y) //press a key to perform actions
{
switch (key) {
case 'd': d[0] += 0.1; break; //camera right
case 'a': d[0] -= 0.1; break; //camera left
case 'w': d[1] += 0.1; break; //camera up
case 's': d[1] -= 0.1; break; //camera down
case 'm': d[2] += 0.1; break; //magnify
case 'n': d[2] -= 0.1; break; //minify
case 't': draw_triangle = true; draw_decagon = false; break; //draw pyramid when key is pressed
case 'q': draw_square = true; draw_decagon = false; draw_triangle = false; break; //draw cube when key is pressed
case 'l': draw_decagon = true; draw_triangle = false; draw_square = false; break; //draw prism when key is pressed
case 'x': xAngle += 5; break; //modify x axis angle
case 'y': yAngle += 5; break; //modify y axis angle
case 'z': zAngle += 5; break; //modify z axis angle
default: printf(" Keyboard %c == %d", key, key); //see what key it's pressed
}
glutPostRedisplay();
}
void spinDisplay() //here it's the problematic function
{
spin = spin + 0.1;
if (spin > 360.0)
{
spin = 0.0;
}
glutPostRedisplay();
}
void mouse(int buton, int state, int x, int y)
{
switch (buton) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(spinDisplay);
break;
case GLUT_RIGHT_BUTTON: //here I don't know how to change the color of the shape
glutIdleFunc(NULL);
default:glutIdleFunc(NULL);
break;
}
}
void redraw(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glLoadIdentity();
glTranslatef(0, 0, -3);
glRotatef(tippangle, 1, 0, 0); // Up and down arrow keys 'tip' view.
glRotatef(viewangle, 0, 1, 0); // Right/left arrow keys 'turn' view.
glDisable(GL_LIGHTING);
glPushMatrix();
glTranslatef(d[0], d[1], d[2]); // Move box down X axis.
glScalef(0.7f, 0.7f, 0.7f); //increase the object size
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
if (draw_triangle)
Triangle();
if (draw_decagon)
Decagon();
if (draw_square)
Square();
glPopMatrix();
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitWindowSize(900, 600);
glutInitWindowPosition(300, 300);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE);
glutCreateWindow("Figure Rotation");
glutDisplayFunc(redraw);
glutKeyboardFunc(Keyboard);
glutMouseFunc(mouse);
glClearColor(0.1, 0.0, 0.1, 1.0);
glMatrixMode(GL_PROJECTION);//specify which matrix is the current matrix, matrix that represents your camera's lens (aperture, far-field, near-field, etc).
gluPerspective(60, 1.5, 1, 10); //set up a perspective projection matrix
glMatrixMode(GL_MODELVIEW); //specify which matrix is the current matrix,matrix that represents your camera (position, pointing, and up vector).
glutMainLoop();
return 1;
}
仅根据您的代码,主要问题在于 Decagon()
的形状顶点定义。
由于这样的顶点不是在形状本身的中心定义的,而是在右上角定义的,因此它不会围绕自身旋转但似乎围绕中心旋转,尽管您的矩阵乘法序列工作正常。
为简单起见,我将其可视化为沿 xy 平面将其置于 0,0
中心,然后定义其形状的右半部分,然后将其镜像回左侧。您可以利用 -
减号。隐含地利用在 NDC (Normalizd Device Coordinate) space.
中定义形状
注意:与您最初定义的比率不完全相同,但可以让您了解一下。你可以试着把下面的换成你的,然后它应该绕着自己旋转。
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.25f, 0.5f, 0.0f);
glVertex3f(0.45f, 0.30f, 0.0f);
glVertex3f(0.55f, 0.0f, 0.0f);
glVertex3f(0.45f, -0.30f, 0.0f);
glVertex3f(0.25f, -0.5f, 0.0f);
glVertex3f(-0.25f, -0.5f, 0.0f);
glVertex3f(-0.45f, -0.30f, 0.0f);
glVertex3f(-0.55f, 0.0f, 0.0f);
glVertex3f(-0.45f, 0.30f, 0.0f);
glVertex3f(-0.25f, 0.5f, 0.0f);
//glScalef(10, 10, 10); // this won't have any effect on result
//glTranslatef(1, 2, -3);// the same
glEnd();
这里有 2 个选项
- 完全改变顶点定义(只有
Decagon
与上面相对于原点的相似)。其他形状已经好了,是相对于原点定义的。
- 无论您定义的形状的顶点如何,都要仔细确定形状的原点。在所有其他操作之前,首先使用这样的位置将形状转换回矩阵操作的一部分(请继续阅读以了解原因)。
绕自身旋转的概念
围绕自身旋转的概念就是我们需要依次进行以下操作
- 规模(在这种情况下我们没有)
- 旋转
- 翻译
缩放虽然我们在这种情况下没有,但应该放在最后,否则可能会影响其他两个操作。
如果我们先平移到任意位置,那么旋转将围绕该点发生。其实旋转是相对于原点的0,0
,因此我们只需要在继续之前无论如何将物体放回原点,然后我们就可以旋转,平移到它应该的位置,并且规模.
让我们看看你的矩阵乘法顺序
glScalef(0.7f, 0.7f, 0.7f); //increase the object size
glTranslatef(d[0], d[1], d[2]); // Move box down X axis.
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
这意味着我们按顺序执行以下操作
- 绕z轴旋转
spin
角度
- 绕x轴旋转
xAngle
角度
- 绕y轴旋转
yAngle
角度
- 绕z轴旋转
zAngle
角度
虽然我们可以把第一个和最后一个结合起来,但是没关系。
Also you might want to further look at Euler Angles when we rotate around 3 cardinal axes like this, it can lead to Gimbal lock problem but it can be solved by limiting angles user can rotate around a certain axis.
顺序是对的。这被翻译成数学术语 S * T * Rz * Ry * Rx * Rspin
,您可以在其中看到它与代码中的顺序相反。 Rspin
先发生,然后 Rx
然后依此类推。
现在,如果 Decagon
形状定义为 而非 相对于原点,而是以向右平移的方式定义,会发生什么情况。
采用我的顶点定义,但是 + 0.55f
对于所有 x 位置,我们将有
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.80f, 0.5f, 0.0f);
glVertex3f(1.0f, 0.30f, 0.0f);
glVertex3f(1.10f, 0.0f, 0.0f);
glVertex3f(1.0f, -0.30f, 0.0f);
glVertex3f(0.80f, -0.5f, 0.0f);
glVertex3f(0.30f, -0.5f, 0.0f);
glVertex3f(0.10f, -0.30f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(0.1f, 0.30f, 0.0f);
glVertex3f(0.30f, 0.5f, 0.0f);
glEnd();
如果您将上面的代码替换为您的顶点定义,那么它就不会再围绕自身旋转了。但是我们知道 x 轴需要 -0.55f
才能使这个形状回到原点,因此如果我们添加 glTranslatef(-0.55f, 0.0f, 0.0f)
作为第一个要执行的操作,那么它的工作原理是一样的。
我们会
glScalef(0.7f, 0.7f, 0.7f);
glTranslatef(d[0], d[1], d[2]);
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
glTranslatef(-0.55f, 0.0f, 0.0f); // <------ add this
简而言之,先将目标对象平移到原点,然后再旋转(围绕自身),然后像以前一样进行适当的顺序。
If you desire to have such object to be located at the location you've defined the shape's vertices i.e. it's to the right +0.55f
along x-axis and still rotate around itself. Then you use glTranslatef(d[0] + 0.55f, d[1], d[2])
instead.
进一步说明
- 最后两个 gl 操作
glScalef()
和 glTranslatef()
不会有任何效果,因为您已经绘制了形状。当您调用 glLoadIdentity()
. 时,这两个操作每帧都会被丢弃
- 请注意,源代码仍然基于OpenGL 的固定功能管道。您可能还想看看现代可编程管道。这将允许您更灵活地控制 虚拟 相机,因此矩阵操作更加清晰,并且在我们需要四处移动时与对象本身分离。所以这将使矩阵运算更容易掌握和理解。
编辑
额外控制和满足应用要求如下
- 左键单击无限旋转,然后再次左键单击停止
- 右键单击以循环显示渲染形状的颜色
我们必须有控制标志,以及我们可以在任何帧时间更改的信息,如下所示。
bool isSpinning = false;
#define NUM_COLOR 4
int sCurrColor = 0;
GLfloat sColor[NUM_COLOR][3] = {
{1.0f, 1.0f, 1.0f},
{1.0f, 0.0f, 0.0f},
{0.0f, 1.0f, 0.0f},
{0.0f, 0.0f, 1.0f}
};
所以对于颜色,我们有白色、红色、蓝色和绿色。共有 4 种颜色,每种颜色有 3 个 RGB 分量值。我们从索引 sCurrColor
中看到的白色开始。
现在你的 mouse()
函数看起来像这样
void mouse(int buton, int state, int x, int y)
{
switch (buton) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN && !isSpinning)
isSpinning = true;
else if (state == GLUT_DOWN && isSpinning)
isSpinning = false;
break;
case GLUT_RIGHT_BUTTON: //here I don't know how to change the color of the shape
if (state == GLUT_DOWN)
sCurrColor = (sCurrColor + 1) % NUM_COLOR;
break;
default:glutIdleFunc(NULL);
break;
}
}
我们优化了移动 glutIdleFunc(spinDisplay);
以在 main()
函数内部调用 glutMainLoop()
。根据您的要求,我们不必每帧都更改它。
因此,spinDisplay()
现在更改为
void spinDisplay() //here it's the problematic function
{
if (isSpinning)
{
spin = spin + 3.0;
if (spin > 360.0)
{
spin = 0.0;
}
}
glutPostRedisplay();
}
Probably better to change the name of function to something like display()
as it's more generic to not confuse that we have to spin everytime. Anyway, I didn't change this for the sake of brevity and consistency of your code.
现在最后一部分是插入 sColor
以供所有这些形状在渲染中使用。例如 Decagon
你可以这样做
glColor3f(sColor[sCurrColor][0], sColor[sCurrColor][1], sColor[sCurrColor][2]);
如果您希望通过右键单击以循环显示颜色来获得相同的效果,这对于其他形状也是一样的。
我成功地旋转了我的对象,但我需要右键单击该对象以停止其旋转。我不知道如何使对象绕其中心旋转然后停止,我将附上代码以查看此形状到底发生了什么。我认为问题出在 spinDisplay()
函数上……问题是我需要在单击鼠标左键时围绕它的中心旋转,而在单击鼠标右键时我应该更改对象的颜色…… .
#include <stdlib.h>
#include <math.h>
#include "dependente\freeglut\freeglut.h"
#include "dependente\glfw\glfw3.h"
#include <stdio.h> //incluziuni librarii
float ORG[3] = { 0,0,0 };
static GLfloat spin = 0.0;
GLfloat viewangle = 0, tippangle = 0, traj[120][3]; //variabila pentru unghi camera
GLfloat d[3] = { 0.1, 0.1, 0.1 }; //vector directie
GLfloat xAngle = 0.0, yAngle = 0.0, zAngle = 0.0;
bool draw_triangle = false; //variabila desenat figuri
bool draw_square = false;
bool draw_decagon = false;
void Triangle(void) //draw the triangle shape
{
glBegin(GL_TRIANGLE_FAN);//triangles have a common vertex, which is the central vertex
glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(0.0f, 1.0f, 0.0f); //V0(red)
glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); //V1(green)
glColor3f(0.0f, 0.0f, 1.0f); glVertex3f(1.0f, -1.0f, 1.0f); //V2(blue)
glEnd();
}
void Square(void) {
glBegin(GL_QUADS);
glVertex2f(-1.0f, 1.0f); // top left
glVertex2f(1.0f, 1.0f); // top right
glVertex2f(1.0f, -1.0f); // bottom right
glVertex2f(-1.0f, -1.0f); // bottom left
glEnd();
}
void Decagon(void) //draw the decagon shape
{
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.72f,0.8f, 0.0f); //a1
glVertex3f(0.52f, 0.8f,0.0f); //z
glVertex3f(0.35f, 0.64f, 0.0f); //b1
glVertex3f(0.3f, 0.48f, 0.0f); //d1
glVertex3f(0.35f, 0.3f, 0.0f); //e1
glVertex3f(0.52f, 0.16f, 0.0f); //l1
glVertex3f(0.72f, 0.16f, 0.0f); //m1
glVertex3f(0.9f, 0.3f, 0.0f); //o1
glVertex3f(0.95f, 0.48f, 0.0f); //p1
glVertex3f(0.9f, 0.64f, 0.0f); //c1
glScalef(10, 10, 10);
glTranslatef(1, 2, 3);
glEnd();
}
void Keyboard(unsigned char key, int x, int y) //press a key to perform actions
{
switch (key) {
case 'd': d[0] += 0.1; break; //camera right
case 'a': d[0] -= 0.1; break; //camera left
case 'w': d[1] += 0.1; break; //camera up
case 's': d[1] -= 0.1; break; //camera down
case 'm': d[2] += 0.1; break; //magnify
case 'n': d[2] -= 0.1; break; //minify
case 't': draw_triangle = true; draw_decagon = false; break; //draw pyramid when key is pressed
case 'q': draw_square = true; draw_decagon = false; draw_triangle = false; break; //draw cube when key is pressed
case 'l': draw_decagon = true; draw_triangle = false; draw_square = false; break; //draw prism when key is pressed
case 'x': xAngle += 5; break; //modify x axis angle
case 'y': yAngle += 5; break; //modify y axis angle
case 'z': zAngle += 5; break; //modify z axis angle
default: printf(" Keyboard %c == %d", key, key); //see what key it's pressed
}
glutPostRedisplay();
}
void spinDisplay() //here it's the problematic function
{
spin = spin + 0.1;
if (spin > 360.0)
{
spin = 0.0;
}
glutPostRedisplay();
}
void mouse(int buton, int state, int x, int y)
{
switch (buton) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(spinDisplay);
break;
case GLUT_RIGHT_BUTTON: //here I don't know how to change the color of the shape
glutIdleFunc(NULL);
default:glutIdleFunc(NULL);
break;
}
}
void redraw(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glLoadIdentity();
glTranslatef(0, 0, -3);
glRotatef(tippangle, 1, 0, 0); // Up and down arrow keys 'tip' view.
glRotatef(viewangle, 0, 1, 0); // Right/left arrow keys 'turn' view.
glDisable(GL_LIGHTING);
glPushMatrix();
glTranslatef(d[0], d[1], d[2]); // Move box down X axis.
glScalef(0.7f, 0.7f, 0.7f); //increase the object size
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
if (draw_triangle)
Triangle();
if (draw_decagon)
Decagon();
if (draw_square)
Square();
glPopMatrix();
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitWindowSize(900, 600);
glutInitWindowPosition(300, 300);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE);
glutCreateWindow("Figure Rotation");
glutDisplayFunc(redraw);
glutKeyboardFunc(Keyboard);
glutMouseFunc(mouse);
glClearColor(0.1, 0.0, 0.1, 1.0);
glMatrixMode(GL_PROJECTION);//specify which matrix is the current matrix, matrix that represents your camera's lens (aperture, far-field, near-field, etc).
gluPerspective(60, 1.5, 1, 10); //set up a perspective projection matrix
glMatrixMode(GL_MODELVIEW); //specify which matrix is the current matrix,matrix that represents your camera (position, pointing, and up vector).
glutMainLoop();
return 1;
}
仅根据您的代码,主要问题在于 Decagon()
的形状顶点定义。
由于这样的顶点不是在形状本身的中心定义的,而是在右上角定义的,因此它不会围绕自身旋转但似乎围绕中心旋转,尽管您的矩阵乘法序列工作正常。
为简单起见,我将其可视化为沿 xy 平面将其置于 0,0
中心,然后定义其形状的右半部分,然后将其镜像回左侧。您可以利用 -
减号。隐含地利用在 NDC (Normalizd Device Coordinate) space.
注意:与您最初定义的比率不完全相同,但可以让您了解一下。你可以试着把下面的换成你的,然后它应该绕着自己旋转。
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.25f, 0.5f, 0.0f);
glVertex3f(0.45f, 0.30f, 0.0f);
glVertex3f(0.55f, 0.0f, 0.0f);
glVertex3f(0.45f, -0.30f, 0.0f);
glVertex3f(0.25f, -0.5f, 0.0f);
glVertex3f(-0.25f, -0.5f, 0.0f);
glVertex3f(-0.45f, -0.30f, 0.0f);
glVertex3f(-0.55f, 0.0f, 0.0f);
glVertex3f(-0.45f, 0.30f, 0.0f);
glVertex3f(-0.25f, 0.5f, 0.0f);
//glScalef(10, 10, 10); // this won't have any effect on result
//glTranslatef(1, 2, -3);// the same
glEnd();
这里有 2 个选项
- 完全改变顶点定义(只有
Decagon
与上面相对于原点的相似)。其他形状已经好了,是相对于原点定义的。 - 无论您定义的形状的顶点如何,都要仔细确定形状的原点。在所有其他操作之前,首先使用这样的位置将形状转换回矩阵操作的一部分(请继续阅读以了解原因)。
绕自身旋转的概念
围绕自身旋转的概念就是我们需要依次进行以下操作
- 规模(在这种情况下我们没有)
- 旋转
- 翻译
缩放虽然我们在这种情况下没有,但应该放在最后,否则可能会影响其他两个操作。
如果我们先平移到任意位置,那么旋转将围绕该点发生。其实旋转是相对于原点的0,0
,因此我们只需要在继续之前无论如何将物体放回原点,然后我们就可以旋转,平移到它应该的位置,并且规模.
让我们看看你的矩阵乘法顺序
glScalef(0.7f, 0.7f, 0.7f); //increase the object size
glTranslatef(d[0], d[1], d[2]); // Move box down X axis.
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
这意味着我们按顺序执行以下操作
- 绕z轴旋转
spin
角度 - 绕x轴旋转
xAngle
角度 - 绕y轴旋转
yAngle
角度 - 绕z轴旋转
zAngle
角度
虽然我们可以把第一个和最后一个结合起来,但是没关系。
Also you might want to further look at Euler Angles when we rotate around 3 cardinal axes like this, it can lead to Gimbal lock problem but it can be solved by limiting angles user can rotate around a certain axis.
顺序是对的。这被翻译成数学术语 S * T * Rz * Ry * Rx * Rspin
,您可以在其中看到它与代码中的顺序相反。 Rspin
先发生,然后 Rx
然后依此类推。
现在,如果 Decagon
形状定义为 而非 相对于原点,而是以向右平移的方式定义,会发生什么情况。
采用我的顶点定义,但是 + 0.55f
对于所有 x 位置,我们将有
glBegin(GL_POLYGON);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f(0.80f, 0.5f, 0.0f);
glVertex3f(1.0f, 0.30f, 0.0f);
glVertex3f(1.10f, 0.0f, 0.0f);
glVertex3f(1.0f, -0.30f, 0.0f);
glVertex3f(0.80f, -0.5f, 0.0f);
glVertex3f(0.30f, -0.5f, 0.0f);
glVertex3f(0.10f, -0.30f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(0.1f, 0.30f, 0.0f);
glVertex3f(0.30f, 0.5f, 0.0f);
glEnd();
如果您将上面的代码替换为您的顶点定义,那么它就不会再围绕自身旋转了。但是我们知道 x 轴需要 -0.55f
才能使这个形状回到原点,因此如果我们添加 glTranslatef(-0.55f, 0.0f, 0.0f)
作为第一个要执行的操作,那么它的工作原理是一样的。
我们会
glScalef(0.7f, 0.7f, 0.7f);
glTranslatef(d[0], d[1], d[2]);
glRotatef(zAngle, 0, 0, 1);
glRotatef(yAngle, 0, 1, 0);
glRotatef(xAngle, 1, 0, 0);
glRotatef(spin, 0.0, 0.0, 1.0);
glTranslatef(-0.55f, 0.0f, 0.0f); // <------ add this
简而言之,先将目标对象平移到原点,然后再旋转(围绕自身),然后像以前一样进行适当的顺序。
If you desire to have such object to be located at the location you've defined the shape's vertices i.e. it's to the right
+0.55f
along x-axis and still rotate around itself. Then you useglTranslatef(d[0] + 0.55f, d[1], d[2])
instead.
进一步说明
- 最后两个 gl 操作
glScalef()
和glTranslatef()
不会有任何效果,因为您已经绘制了形状。当您调用glLoadIdentity()
. 时,这两个操作每帧都会被丢弃
- 请注意,源代码仍然基于OpenGL 的固定功能管道。您可能还想看看现代可编程管道。这将允许您更灵活地控制 虚拟 相机,因此矩阵操作更加清晰,并且在我们需要四处移动时与对象本身分离。所以这将使矩阵运算更容易掌握和理解。
编辑 额外控制和满足应用要求如下
- 左键单击无限旋转,然后再次左键单击停止
- 右键单击以循环显示渲染形状的颜色
我们必须有控制标志,以及我们可以在任何帧时间更改的信息,如下所示。
bool isSpinning = false;
#define NUM_COLOR 4
int sCurrColor = 0;
GLfloat sColor[NUM_COLOR][3] = {
{1.0f, 1.0f, 1.0f},
{1.0f, 0.0f, 0.0f},
{0.0f, 1.0f, 0.0f},
{0.0f, 0.0f, 1.0f}
};
所以对于颜色,我们有白色、红色、蓝色和绿色。共有 4 种颜色,每种颜色有 3 个 RGB 分量值。我们从索引 sCurrColor
中看到的白色开始。
现在你的 mouse()
函数看起来像这样
void mouse(int buton, int state, int x, int y)
{
switch (buton) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN && !isSpinning)
isSpinning = true;
else if (state == GLUT_DOWN && isSpinning)
isSpinning = false;
break;
case GLUT_RIGHT_BUTTON: //here I don't know how to change the color of the shape
if (state == GLUT_DOWN)
sCurrColor = (sCurrColor + 1) % NUM_COLOR;
break;
default:glutIdleFunc(NULL);
break;
}
}
我们优化了移动 glutIdleFunc(spinDisplay);
以在 main()
函数内部调用 glutMainLoop()
。根据您的要求,我们不必每帧都更改它。
因此,spinDisplay()
现在更改为
void spinDisplay() //here it's the problematic function
{
if (isSpinning)
{
spin = spin + 3.0;
if (spin > 360.0)
{
spin = 0.0;
}
}
glutPostRedisplay();
}
Probably better to change the name of function to something like
display()
as it's more generic to not confuse that we have to spin everytime. Anyway, I didn't change this for the sake of brevity and consistency of your code.
现在最后一部分是插入 sColor
以供所有这些形状在渲染中使用。例如 Decagon
你可以这样做
glColor3f(sColor[sCurrColor][0], sColor[sCurrColor][1], sColor[sCurrColor][2]);
如果您希望通过右键单击以循环显示颜色来获得相同的效果,这对于其他形状也是一样的。