用鼠标在 OpenGL GLUT 中绘制多边形

Question

我想在 openGL Glut 中通过鼠标交互绘制一个多边形，每次左键单击都会成为一个顶点，并且会在每个顶点之间绘制一条线。单击鼠标右键时，多边形将关闭从最后一个顶点到第一个顶点绘制一条线。我想到了这个，但它似乎不起作用。

void draw_polygon(int button, int state, int x, int y) {

    bool right_pushed = 0;
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_POINTS);

    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
        p1.x = x;
        p1.y = 480 - y;

        //if right is clicked draw a line to here
        first.x = x;
        first.y = 480 - y;
    }

    while (right_pushed == false) {

        if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
            p2.x = x;
            p2.y = 480 - y;
        }

        GLfloat dx = p2.x - p1.x;
        GLfloat dy = p2.y - p1.y;

        GLfloat x1 = p1.x;
        GLfloat y1 = p1.y;

        GLfloat step = 0;

        if (abs(dx) > abs(dy)) {
            step = abs(dx);
        }
        else {
            step = abs(dy);
        }

        GLfloat xInc = dx / step;
        GLfloat yInc = dy / step;


        for (float i = 1; i <= step; i++) {
            glVertex2i(x1, y1);
            x1 += xInc;
            y1 += yInc;
        }


        p1.x = p2.x;
        p1.y = 480 - y;

        if (button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN) {

            right_pushed = 1;
            p2.x = first.x;
            p2.y = first.y;

            dx = p2.x - p1.x;
            dy = p2.y - p1.y;

            x1 = p1.x;
            y1 = p1.y;

            step = 0;

            if (abs(dx) > abs(dy)) {
                step = abs(dx);
            }
            else {
                step = abs(dy);
            }

            xInc = dx / step;
            yInc = dy / step;


            for (float i = 1; i <= step; i++) {

                glVertex2i(x1, y1);
                x1 += xInc;
                y1 += yInc;

            }

        }
    }

    glEnd();
    glFlush();


}

int main(int argc, char **argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition(200, 200);
    glutInitWindowSize(640, 480);
    glutCreateWindow("windows");
    glutDisplayFunc(display);
    glutMouseFunc(draw_polygon);//
    init();
    glutMainLoop();
    return 0;
}

我也在尝试找出如何添加一个功能，当我从菜单中 select 时，我可以从创建这个多边形到以我可以 select 的方式编辑它vertex ，左右移动，形状随之变化

Answer 1

你必须把鼠标事件和绘图函数分开。

在鼠标事件中，您应该只收集输入。我建议为此使用 std::vector。如果按下鼠标左键，以下函数会向 std::vector 添加一个点。如果按下右键，多边形被标记为关闭。如果再次按下左键，多边形将被清除并重新开始。

#include <vector>
#include <array>

int vp_width = 640;
int vp_height = 480;

std::array<int, 2> currentPt;
std::vector<std::array<int, 2>> pts;
bool closed = false;

void draw_polygon(int button, int state, int x, int y)
{
    currentPt = std::array<int, 2>{x, vp_height-y}; 

    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
    {
        if ( closed )
            pts.clear(); // restart if last action was close
        closed = false;
        pts.push_back( currentPt );
    }
    if ( button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN )
        closed = true;
}

在鼠标移动事件函数中，您可以跟踪当前鼠标位置：

void mouse_move(int x, int y)
{
    currentPt = std::array<int, 2>{x, vp_height-y};
    glutPostRedisplay();
}

在您的主循环中，您可以连续绘制当前点之间的线。下面的函数在点列表之间画线。如果设置了 "cloesd" 标志，则多边形被关闭。否则绘制从列表中的最后一个点到当前鼠标位置的线。

void display(void)
{
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);

    if ( !pts.empty() )
    {
        glBegin(GL_LINE_STRIP);
        for ( auto &pt : pts )
            glVertex2f( (float)pt[0], (float)pt[1] );
        auto &endPt = closed ? pts.front() : currentPt;
        glVertex2f( (float)endPt[0], (float)endPt[1] );
        glEnd();
    }

    //glFlush();
    glutSwapBuffers();
}

int main()
{
    ..... 
    glutDisplayFunc(display);
    glutPassiveMotionFunc (mouse_move);
    glutMouseFunc(draw_polygon);

    glMatrixMode( GL_PROJECTION );
    glOrtho(0.0f, (float)vp_width, 0.0f, (float)vp_height, -1.0, 1.0);
    .....
}

预览：

用鼠标在 OpenGL GLUT 中绘制多边形

Draw a polygon in OpenGL GLUT with mouse

c++

opengl

graphics

glut

opengl-compat