【OpenGL】9-鼠标与键盘

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参考教程

【中文版】第六课：键盘和鼠标

【英文版】Tutorial 6 : Keyboard and Mouse

学习笔记

  上一篇文章中我们使用了矩阵运算让正方体实现了平移旋转等操作，不过都是用我们设定好的值进行变换，这一篇中我们将实现使用鼠标API使得正方体在X，Y平面上随鼠标移动，并且使用W，A，S，D和Up，Down，Left，Right等键位控制关于X，Y轴的旋转。

  首先贴出我们使用到的鼠标的API glfwGetCursorPos，glfwSetCursorPos，这两个API的作用通过名字便可以猜出来一个是Get光标位置，一个是Set光标位置，我们需要让正方体跟随鼠标移动，那么肯定需要调用Get方法。

  首先看一下官方的API描述：

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void glfwGetCursorPos   (   GLFWwindow *    window,                          
                         	 double *    xpos,                       
                         	 double *    ypos 
)

  This function returns the position of the cursor, in screen coordinates, relative to the upper-left corner of the client area of the specified window.

  If the cursor is disabled (with GLFW_CURSOR_DISABLED) then the cursor position is unbounded and limited only by the minimum and maximum values of a double.

  The coordinate can be converted to their integer equivalents with the floor function. Casting directly to an integer type works for positive coordinates, but fails for negative ones.

  Any or all of the position arguments may be NULL. If an error occurs, all non-NULL position arguments will be set to zero.

  • Parameters

    [in]windowThe desired window.[out]xposWhere to store the cursor x-coordinate, relative to the left edge of the client area, or NULL.[out]yposWhere to store the cursor y-coordinate, relative to the to top edge of the client area, or NULL.

  • Thread safety

    This function must only be called from the main thread.

  我们使用glfwGetCursorPos可以获得光标的坐标，由于平移操作是相对于上一刻所对应的位置进行计算，所以我们需要保存上一刻的坐标和当前坐标，如下：

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double preX = width / 2, preY = height / 2;
double curX = preX, curY = preY;
//do something
glfwGetCursorPos(window, &curX, &curY);
preX = curX;
preY = curY;

  平移的X，Y参数也修改为

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Model = Model * glm::translate(glm::mat4(), glm::vec3(curX-preX, curY-preY, 0.0f));

  点击运行，发现打开之后立方体消失了，怎么回事？

  其实是因为打开的那一瞬间，我们的鼠标光标一般不会在显示的正中心，又因为一次性平移的幅度太大，所以超出了可显示区域。这种时候，我们需要用glfwSetCursorPos固定光标到最中心，并且修改glm::translate中的X，Y将其缩小到百分之一。如下：

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double preX = width / 2, preY = height / 2;
double curX = preX, curY = preY;
glfwSetCursorPos(window , curX , curY);
do {
    glfwGetCursorPos(window, &curX, &curY);
    Model = Model * glm::translate(glm::mat4(), glm::vec3((curX-preX)/100, (curY-preY)/100, 0.0f));
    preX = curX;
    preY = curY;
    ...
} while(...)

  Ok，现在启动之后动动鼠标，是不是正方体跟随鼠标移动而移动啦。

  搞定了跟随鼠标平移，那么现在我们需要实现的是使用W，A，S，D或者Up，Down，Left，Right进行旋转。首先需要看一下我们读取键盘的方法glfwGetKey：

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int glfwGetKey	(	GLFWwindow * 	window,
					int 	key 
)

  This function returns the last state reported for the specified key to the specified window. The returned state is one of GLFW_PRESS or GLFW_RELEASE. The higher-level action GLFW_REPEAT is only reported to the key callback.

  If the GLFW_STICKY_KEYS input mode is enabled, this function returns GLFW_PRESS the first time you call it for a key that was pressed, even if that key has already been released.

  The key functions deal with physical keys, with key tokens named after their use on the standard US keyboard layout. If you want to input text, use the Unicode character callback instead.

  The modifier key bit masks are not key tokens and cannot be used with this function.

Do not use this function to implement text input.

  • Parameters

    [in]windowThe desired window.[in]keyThe desired keyboard key. GLFW_KEY_UNKNOWN is not a valid key for this function.

  • Returns

    One of GLFW_PRESS or GLFW_RELEASE.

  • Thread safety

    This function must only be called from the main thread.

  这个方法需要我们传一个Window参数和一个键盘标识符，返回是否按键，使用如下：

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if(glfwGetKey(window , GLFW_KEY_UP)){ //当按Up键的时候
            ...
        }

  现在我们需要按Up键的时候正方体绕X轴逆时针旋转，自然可以这样写：

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if(glfwGetKey(window , GLFW_KEY_UP)){
            Model = Model * glm::rotate(glm::mat4() , glm::radians(15.0f), glm::vec3(-1.0f, 0.0f, 0.0f));
        }

  其他几个也类似：

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if(glfwGetKey(window , GLFW_KEY_UP) || glfwGetKey(window , GLFW_KEY_W)){
    Model = Model * glm::rotate(glm::mat4() , glm::radians(15.0f), glm::vec3(-1.0f, 0.0f, 0.0f));
}

if(glfwGetKey(window , GLFW_KEY_DOWN) || glfwGetKey(window , GLFW_KEY_S)){
    Model = Model * glm::rotate(glm::mat4() , glm::radians(15.0f), glm::vec3(1.0f, 0.0f, 0.0f));
}

if(glfwGetKey(window , GLFW_KEY_LEFT) || glfwGetKey(window , GLFW_KEY_A)){
    Model = Model * glm::rotate(glm::mat4() , glm::radians(15.0f), glm::vec3(0.0f, -1.0f, 0.0f));
}

if(glfwGetKey(window , GLFW_KEY_RIGHT) || glfwGetKey(window , GLFW_KEY_D)){
    Model = Model * glm::rotate(glm::mat4() , glm::radians(15.0f), glm::vec3(0.0f, 1.0f, 0.0f));
}

  不会Markdown上传短视频，所以具体效果只能自己尝试运行了，如果有什么地方卡壳的话，可以看这里源代码。

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