Opengl 鼠标点击矩形
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【中文标题】Opengl 鼠标点击矩形【英文标题】：Opengl Mouse click on rectangle 【发布时间】：2016-02-11 09:18:43 【问题描述】：伙计们，我在使用 glut 鼠标功能时遇到了这个程序的问题。我在做什么 在屏幕上绘制一个矩形，在鼠标功能中，我将像素坐标转换为宽度为 600 和高度为 500 的世界坐标如何确定鼠标点击这些矩形。 代码：
#include <cstdlib>
#include<GL\freeglut.h>
#include <iostream>
using namespace std;
float xWorldCoordinate = 0.0f;
float yWorldCoordinate = 0.0f;
float r = 0.0f;
float g = 0.0f;
float b = 0.0f;
float r1 = 0.0f;
float g1 = 0.0f;
float b1 = 0.0f;
bool isRed = false;
void init(void)
glClearColor(31.0f / 255, 28.0f / 255, 44.0f / 255, 0.0f);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
void MouseButton(int button, int action, int xPixel, int yPixel)
if (button == GLUT_LEFT_BUTTON && action == GLUT_DOWN)
yPixel = 500 - yPixel;
xWorldCoordinate = (xPixel / 600.0f) * 2;
yWorldCoordinate = (yPixel / 400.0f) * 2;
xWorldCoordinate = -1 + xWorldCoordinate;
yWorldCoordinate = -1 + yWorldCoordinate;
int index1 = 0;
int index2 = 0;
//Index1
glReadPixels(xPixel, yPixel, 1, 1, GL_STENCIL_INDEX, GL_UNSIGNED_INT, &index1);// Read pixel under mouse's cursor and read information from stencil buffer to index when it rectangle index should be equal to 1
if (index1 == 1)
isRed = !isRed;
if (isRed)
r = 0.0f;
else
r = 1.0f;
//Index 2
// glReadPixels(xPixel, yPixel, 1, 1, GL_STENCIL_INDEX, GL_UNSIGNED_INT, &index2);
glutPostRedisplay();
void Rectangles(void)
glStencilFunc(GL_ALWAYS, 1, -1); //set front and back function and reference value for stencil testing
glBegin(GL_POLYGON);
glColor3f(r, g, b);
glVertex2f(-0.1f, 0.1f);
glVertex2f(-0.1f, -0.1f);
glVertex2f(0.1f, -0.1f);
glVertex2f(0.1f, 0.1f);
glEnd();
//2nd Rectangle
glStencilFunc(GL_ALWAYS, 2, -1);
glBegin(GL_POLYGON);
glColor3f(r1, g1, b1);
glVertex2f(0.66f, 0.84f);
glVertex2f(0.87f, 0.84f);
glVertex2f(0.87f, 0.66f);
glVertex2f(0.66f, 0.66f);
glEnd();
void Display(void)
glClearStencil(0); // specifies the index used by glClear to clear the stencil buffer
glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
Rectangles();
glFlush();
int main(int argc, char **argv)
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_STENCIL); //Bit mask to select a window with a stencil buffer.
glutInitWindowSize(600, 500);
glutInitWindowPosition(100, 100);
glutCreateWindow("Mouse");
init();
glutDisplayFunc(&Display);
glutMouseFunc(&MouseButton);
glutMainLoop();
return EXIT_SUCCESS;
【问题讨论】：
您试图确定单击时是否单击了矩形，我说得对吗？ @segevara 是的，正是点击它改变颜色 【参考方案1】：我想你可以通过这个来使用 GLUT_STENCIL 你可以通过索引来指示你场景中的所有对象
#if defined(__APPLE__) || defined(MACOSX)
#include <GLUT/glut.h>
#else
#include <GL\freeglut.h>
#endif
#include <cstdlib>
#include <iostream>
using namespace std;
using namespace std;
float xWorldCoordinate = 0.0f;
float yWorldCoordinate = 0.0f;
float r = 0.0f;
float g = 0.0f;
float b = 0.0f;
float r1 = 0.0f;
float g1 = 0.0f;
float b1 = 0.0f;
bool isRed = false;
bool isBlue = false;
void init(void)
glClearColor(31.0f / 255, 28.0f / 255, 44.0f / 255, 0.0f);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
void MouseButton(int button, int action, int xPixel, int yPixel)
if (button == GLUT_LEFT_BUTTON && action == GLUT_DOWN)
yPixel = glutGet(GLUT_WINDOW_HEIGHT) - yPixel;
int * index = new int[1];
//Index1
glReadPixels(xPixel, yPixel, 1, 1, GL_STENCIL_INDEX, GL_UNSIGNED_INT, index);// Read pixel under mouse's cursor and read information from stencil buffer to index when it rectangle index should be equal to 1
if (index[0] == 1)
isRed = !isRed;
if (isRed)
r = 1.0f;
else
r = 0.0f;
//Index 2
// glReadPixels(xPixel, yPixel, 1, 1, GL_STENCIL_INDEX, GL_UNSIGNED_INT, &index2);
else if(index[0] == 2)
isBlue = !isBlue;
if (isBlue)
b1 = 1.0f;
else
b1 = 0.0f;
delete index;
glutPostRedisplay();
void Rectangles(void)
glStencilFunc(GL_ALWAYS, 1, -1); //set front and back function and reference value for stencil testing
glBegin(GL_POLYGON);
glColor3f(r, g, b);
glVertex2f(-0.1f, 0.1f);
glVertex2f(-0.1f, -0.1f);
glVertex2f(0.1f, -0.1f);
glVertex2f(0.1f, 0.1f);
glEnd();
//2nd Rectangle
glStencilFunc(GL_ALWAYS, 2, -1);
glBegin(GL_POLYGON);
glColor3f(r1, g1, b1);
glVertex2f(0.66f, 0.84f);
glVertex2f(0.87f, 0.84f);
glVertex2f(0.87f, 0.66f);
glVertex2f(0.66f, 0.66f);
glEnd();
void Display(void)
glClearStencil(0); // specifies the index used by glClear to clear the stencil buffer
glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
Rectangles();
glFlush();
int main(int argc, char **argv)
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_STENCIL); //Bit mask to select a window with a stencil buffer.
glutInitWindowSize(600, 500);
glutInitWindowPosition(100, 100);
glutCreateWindow("Mouse");
init();
glutDisplayFunc(&Display);
glutMouseFunc(&MouseButton);
glutMainLoop();
return EXIT_SUCCESS;
它适用于我在 Mac 上，但我认为也应该适用于 freeglut
【讨论】：
感谢您的回答，它有效，您能帮我解决这个问题吗***.com/questions/35310028/… 我不明白这段代码是如何工作的glReadPixels(xPixel, yPixel - 1, 1, 1, GL_STENCIL_INDEX,GL_UNSIGNED_INT, &index) 。我知道这个函数的参数，但在 y 坐标中你为什么写 yPixel - 1 。你也可以只写yPixel 为什么你写-1，你如何写宽度和高度1。在最后一个参数data 之后，你写了&index 它如何自动将值初始化为 1 并返回地址 1 你能解释一下吗？我在这一行很困惑
我编辑了我的问题代码，如果我现在制作两个矩形而不是它应该如何工作，你能帮我吗..
@hamel123 实际上你是对的，-1 不需要 yPixel。 glReadPixels 可以从一组像素中读取信息，在我们的例子中，我们希望只从一个像素中读取信息，因此我们希望只从一个像素中读取信息，因此您可以通过有趣的矩形来指示这些像素组中的信息 (x,y) 和适当的高度和宽度，因此 height and width 是 1。glReadPixels 还读取缓冲区中的信息，您在我们的例子中的参数中指示我们只需要一个数字情况，我们只读取一个像素，所以我给 glReadPixels 变量的地址，我需要它从模板缓冲区中放置信息。
@hamel123 我刚刚编辑了两个矩形的代码，如果它适合你，请告诉我以上是关于Opengl 鼠标点击矩形的主要内容，如果未能解决你的问题，请参考以下文章