c++ - 缩放 3D 形状(OpenGL 和 C++)

Question

我在 OpenGL 中创建了一个程序来绘制一些形状。我希望用户能够根据需要放大形状。这是绘制形状的代码:

/*Initialise the required OpenGL functions*/
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(0.0, screenWidth, screenHeight, 0.0, -1.0, 10.0);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glDisable(GL_CULL_FACE);
glClear(GL_DEPTH_BUFFER_BIT);

/*Draw a square*/
glColor3f(1, 0, 0);
glBegin(GL_QUADS);
glVertex2f(screenWidth * 0.75, screenHeight * 0.08333);
glVertex2f(screenWidth * 0.75, screenHeight * 0.16666);
glVertex2f(screenWidth * 0.86666, screenHeight * 0.16666);
glVertex2f(screenWidth * 0.86666, screenHeight * 0.08333);
glEnd();
glColor3f(0, 0, 0);

/*Let the user zoom*/
if (GetAsyncKeyState(VK_UP))
{
    /*"zoom" is a global variable*/
    zoom += 0.005;
}

glScaled(1 + zoom, 1 + zoom, 1);

/*Everything that is drawn from this point on (A sphere and a cube) should be scaled*/
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(-0.3, 0, 0);
glutSolidSphere(3, 20, 20);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.55, 0.36, 0);
glutSolidCube(0.05);

glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
glPopMatrix();

glutSwapBuffers();

代码正确绘制了形状，但无法缩放形状。我在其他一些函数中使用了类似的代码，所以我认为这可能是因为我使用的是 3D 形状，或者它可能与我多次调用“glMatrixMode”有关。无论哪种方式，我应该如何更改我的代码，以便根据用户输入缩放立方体和球体，但不影响第一个正方形？

Answer 1

glScaled() 改变当前矩阵。因此，一旦您调用 glLoadIdentity()，您就会撤消缩放。您正在对应该消除的 glMatrixMode() 和 glLoadIdentity() 进行大量不必要的调用。所以尝试更像这样的事情:

// You probably don't really need to do these, but if you do, do it once up top.
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glPushMatrix(); // Save the current matrix
glScaled(1 + zoom, 1 + zoom, 1); // Scale it

/*Everything that is drawn from this point on (A sphere and a cube) should be scaled*/
glTranslatef(-0.3, 0, 0);
glutSolidSphere(3, 20, 20);

glTranslatef(0.55, 0.36, 0);
glutSolidCube(0.05);

glPopMatrix(); // Undo the glScaled() call above

glutSwapBuffers();