c - 如何使用 OpenGL 将正方形居中？

Question

我希望我的 2 个方 block 位于下方并位于窗口中央。

我有以下代码:

glBegin(GL_QUADS);
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(-0.8f, 0.1f);
    glVertex2f(-0.2f, 0.1f);
    glVertex2f(-0.2f, 0.7f);
    glVertex2f(-0.8f, 0.7f);

    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(-0.7f, -0.6f);
    glVertex2f(-0.1f, -0.6f);
    glVertex2f(-0.1f,  0.0f);
    glVertex2f(-0.7f,  0.0f);
    glEnd();

结果是:

但是，它并不完全在下面。

怎么做？

Answer 1

为了澄清问题，您应该首先考虑形状的位置和尺寸:

/* It seems that your windows lies on [-1,1][-1,1] square. */
/* dimension of squares: {width, height} 
   here rectangle since width is equal to height 
   The two rectangles have the same dimension.
   */       
float dim[2] = {0.25f, 0.25f};

/* position of the rectangle centers, here you can see that the first is above
   this array must be read like {{x1, y1}, {x2, y2}}
*/
float pos[2][2] = {{0.0f, 0.4f},{0.0f, -0.4f}};


glBegin(GL_QUADS);
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(pos[0][0] - dim[0], pos[0][1] - dim[1]);
    glVertex2f(pos[0][0] + dim[0], pos[0][1] - dim[1]);
    glVertex2f(pos[0][0] + dim[0], pos[0][1] + dim[1]);
    glVertex2f(pos[0][0] - dim[0], pos[0][1] + dim[1]);

    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(pos[1][0] - dim[0], pos[1][1] - dim[1]);
    glVertex2f(pos[1][0] + dim[0], pos[1][1] - dim[1]);
    glVertex2f(pos[1][0] + dim[0], pos[1][1] + dim[1]);
    glVertex2f(pos[1][0] - dim[0], pos[1][1] + dim[1]);        
glEnd();