无法使用 opengl 正确旋转 2D 对象

Question

我正在使用opengl，glfw和glew。我想当用户分别按下左右箭头时，在不移动整个宇宙飞船的情况下旋转飞船的尖端。我试过使用gltransform glrotate，它确实会旋转，但它也会移动我的宇宙飞船。空间运动的输出

objects objects::rotateSpaceship(GLFWwindow * window, objects & sp)
{
    GLfloat spaceship_angle = sp.getAngle();
    GLfloat newAngle = sp.getAngle() + 0.5;
    sp.setAngle(newAngle);
    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);
        GLfloat spaceShipRightLine[] =
        {
            x, y + 80, 0,
            x - 50, y - 50, 0
        };

        GLfloat spaceShipLeftLine[] = {
            x, y + 80, 0,
            x + 50, y - 50, 0
        };
        GLfloat spaceShipMiddleLine[] = {
            sp.x - 30 ,sp.y,0,
            sp.x + 35,sp.y,0
        };

        glPushMatrix();
        glTranslatef(0.0, 0.01, 0.0); // 3. Translate to the object's position.
        glRotatef(sp.getAngle(), 0.0, 0.0, 1.0); // 2. Rotate the object.
        glTranslatef(0.0, 0.01, 0.0); // 1. Translate to the origin. 
        glEnableClientState(GL_VERTEX_ARRAY);
        glVertexPointer(3, GL_FLOAT, 0, spaceShipRightLine);
        glDrawArrays(GL_LINES, 0, 2);
        glDisableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_VERTEX_ARRAY);
        glVertexPointer(3, GL_FLOAT, 0, spaceShipLeftLine);
        glDrawArrays(GL_LINES, 0, 2);
        glDisableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_VERTEX_ARRAY);
        glVertexPointer(3, GL_FLOAT, 0, spaceShipMiddleLine);
        glDrawArrays(GL_LINES, 0, 2);
        glDisableClientState(GL_VERTEX_ARRAY);
        glPopMatrix();
        // Swap front and back buffers
        glfwSwapBuffers(window);
        // Poll for and process events
        glfwPollEvents();
    }
    glfwTerminate();
    return sp;
}

Answer 1

请注意，几十年来，通过glBegin/glEnd序列和固定函数矩阵堆栈绘制已被弃用。阅读有关固定函数管线的信息，并参阅顶点规范和着色器，了解最先进的渲染方式。

---

我想在不移动整个宇宙飞船的情况下旋转宇宙飞船的尖端 [...]

首先，你必须定义枢轴，这是宇宙飞船的"尖端"：

float pivot_x = sp.x;
float pivot_y = sp.y + 80.0f;

要围绕枢轴旋转，

您必须定义一个模型矩阵，该矩阵由倒置枢轴位移，然后旋转（glRotatef）并最终变换回枢轴（glTranslate）：

glTranslatef(pivot_x, pivot_y, 0);
glRotatef(angle, 0, 0, 1);
glTranslatef(-pivot_x, -pivot_y, 0);

最终代码可能如下所示：

float pivot_x = x;
float pivot_y = y + 80.0f;
glPushMatrix();
glTranslatef(pivot_x, pivot_y, 0 );      // 3. Translate to the object's position.
glRotatef(sp.getAngle(), 0.0, 0.0, 1.0); // 2. Rotate the object.
glTranslatef(-pivot_x, -pivot_y, 0.0);   // 1. Translate to the origin. 
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, spaceShipRightLine);
glDrawArrays(GL_LINES, 0, 2);
glDisableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, spaceShipLeftLine);
glDrawArrays(GL_LINES, 0, 2);
glDisableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, spaceShipMiddleLine);
glDrawArrays(GL_LINES, 0, 2);
glDisableClientState(GL_VERTEX_ARRAY);
glPopMatrix();