openGL(c) 画正方形 [英] openGL(c) draw square

问题描述

我需要用 c (openGL) 画一个正方形，我只有 1 个坐标，它是正方形的中心(比方说 0.5,0.5)，我需要画一个正方形 ABCD，每边长 0.2(AB、BC、CD、DA)，我尝试使用下一个函数，但它没有绘制任何内容，

i need to draw a square using c (openGL), i only have 1 coordinate which is the center of the square (lets say 0.5,0.5) and i need to draw a square ABCD with each side 0.2 length (AB,BC,CD,DA), I tried using the next function but it does not draw anything for some reson,

void drawSquare(double x1,double y1,double radius)
{
    glColor3d(0,0,0);
    glBegin(GL_POLYGON);

    double locationX = x1;
    double locationY = x2;
    double r = radius;

    for(double i=0; i <= 360 ; i+=0.1)
    {
        glVertex2d(locationX + radius*i, locationY + radius*i);
    }

    glEnd();
}

有人可以告诉我为什么它不起作用\指向我正确的方向(我不想绘制具有 4 个正常坐标的多边形，但只有 1 个坐标具有给定的半径，谢谢！

can someone please tell me why its not working\point me to the right direction (i do not want to draw polygon with 4 coordinated normally, but with only 1 coordinate with a givven radius, thanks!

推荐答案

您的代码甚至不会画圆.如果有的话，它会很快绘制一条延伸出视图区域的对角线.圆图需要根据半径和角度使用正弦和余弦.

Your code will not even draw a circle. If anything, it will draw a diagonal line extending out of the view area very quickly. A circle plot would need to use sine and cosine, based on the radius and angle.

这个代码我没试过，但是需要更像这样才能画个正方形.

I have not tried this code, but it needs to be more like this to draw a square.

void drawSquare(double x1, double y1, double sidelength)
{
    double halfside = sidelength / 2;

    glColor3d(0,0,0);
    glBegin(GL_POLYGON);

    glVertex2d(x1 + halfside, y1 + halfside);
    glVertex2d(x1 + halfside, y1 - halfside);
    glVertex2d(x1 - halfside, y1 - halfside);
    glVertex2d(x1 - halfside, y1 + halfside);

    glEnd();
}

没有定义法线:也许我应该逆时针走.

There are no normals defined: perhaps I should have travelled counter-clockwise.

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