gluPerspective，glViewport，gluLookAt和GL_PROJECTION和GL_MODELVIEW矩阵 [英] gluPerspective, glViewport, gluLookAt and the GL_PROJECTION and GL_MODELVIEW Matricies

问题描述

我想使用'gluPerspective'，'glViewport'和'gluLookAt'来操纵相机和屏幕.

I want to use 'gluPerspective', 'glViewport' and 'gluLookAt' to manipulate my camera and screen.

我对哪些功能适用于哪种矩阵模式?我应该/我应该按什么顺序使用它们?

Which functions to I apply to which matrix mode? And in what order should I / must I use them?

例如，我正在尝试像这样设置屏幕和摄像头:(但不起作用！)

For example, I am trying to set up my screen and camera like this: (But it is not working!)

glMatrixMode(GL_PROJECTION) // Apply following to projection matrix - is this correct?
glLoadIdentity(); // Reset first
glPerspective(45.0, (double)w/(double)h, 1.0, 200.0); // Set perspective
glViewport(0, 0, w, h); // Set viewport

glMatrixMode(GL_MODELVIEW); // Apply following to modelview - should glViewport come under here?
glLoadIdentity(); // Reset first
gluLookAt(px, py, pz, cx, cy, cz, ux, uy, uz); // Set position, centre and then up vectors
// This surely comes after calling GL_MODELVIEW?

我到处寻找在线文档，并且我了解这些功能，但不了解它们应该去哪里以及以什么顺序排列！

I have looked around for online documentation, and I understand the functions, just not where they should go and in what order!

现在已经几个月了，我将添加一个快速编辑以显示用于OpenGL渲染系统的系统.这是为了帮助将来看到此问题的其他人.

It is several months later now and I am adding a quick edit to show the system I use to render things with OpenGL. This is to help others who see this question in the future.

我主要使用两种方法.

方法1:

此方法将所有内容组合在一起.

This method groups everything together.

// Firstly, the window may have been resized so re-create the viewing area
glViewport(0, 0, width_of_window_rendering_area, height_of_window_rendering area);

这将重新创建视口，以在窗口内部的整个区域上进行渲染.使用sfml，您可以执行诸如window.width()或window.height()之类的操作，或类似操作，具体取决于您所使用的窗口工具包(glut，glfw，sdl等)...

This recreates the viewport for rendering over the entire area of the inside of the window. With sfml, you would do something like window.width() or window.height(), or something similar depending on which windowing toolkit you use (glut, glfw, sdl etc)...

// The second step is to add a projection matrix. There are three main ones I like to use
// Uncomment the one you want
glMatrixMode(GL_PROJECTION); // Tell OpenGL to manipulate the correct matrix stack
glLoadIdentity(); // Reset the projection matrix, or bad things happen after multiple calls to below functions!
// glOrtho( ... ) // Uncomment to use 2D rendering
// gluPerspective( ... ) // Uncomment to use (easy) 3D rendering
glFrustrum( ... ) // Uncomment to use (harder/less intuitive?) 3D rendering
glMatrixMode(GL_MODELVIEW); // I always prefer to leave OpenGL in the modelview manipulation mode.
    // I consider it the "default" and safest mode to leave OpenGL in, as any rogue
    // calls to functions changing its contents is likely to mess up your geometry
    // which should be visible as a problem on the screen, which tells you you need
    // to fix something! Manipulating the other matrix stacks may not show obvious
    // problems.

您需要从'glOrtho'，'gluPerspective'和'glFrustrum'中选择三个.还有"gluOrtho2D"，但要小心使用！ (我更愿意用'glOrtho'指定自己的近平面和远平面.)您还需要用函数的参数替换'...'.

You will need to select one of the three out of 'glOrtho', 'gluPerspective' and 'glFrustrum'. There is also 'gluOrtho2D', but use that with care! (I prefer to specify near and far planes myself with 'glOrtho'.) You need to replace the '...' with your arguments to the function also.

// The third step is to clear the screen and set your camera / geometry position
glClear(GL_COLOR_BUFFER_BIT); // use bitwise OR ('||') with 'GL_DEPTH_BUFFER_BIT' and 'GL_STENCIL_BUFFER_BIT' if required
gluLookAt( ... );
// I like to use gluLookAt, or at least I _italic_used to! Now I implement my own camera...
 // That is another fun thing you should try if you are comfortable with 3D geometry and hard math!

// The fourth step is to draw your scene. You may want to put lighting stuff first or in with the drawing
glutWireTeapot( ... );

方法2:

第二种方法与上面的方法相同，但是将第一步移到了单独的函数中.然后，您必须检测窗口调整大小事件并调用此函数.使用glut时，您可以指定一个回调.使用SFML，您可以在调整窗口大小时检测到事件.我忘记了SDL的工作原理，但这是相似的.我尚未了解glfw的工作原理.

The second method is the same as above, but to move the first step into a separate function. Then you must detect window resize events and call this function. With glut, you can specify a callback. With SFML you can detect an event when the window is resized. I forget how SDL works, but it is similar. I have not yet learned how glfw works.

希望对您有所帮助.

一些OpenGL新手(可能一次也包括我自己)尝试在PROJECTION矩阵上指定摄影机转换. 请勿这样做-我认为这会弄乱照明和其他可能的东西.

Some OpenGL novices (probably myself included at one time) try to specify camera translations on the PROJECTION matrix. Do not do this - I head it messes up lighting and possibly other things.

推荐答案

我将重塑回调函数定义为:

I define my reshape callback function as:

从头开始呼叫glViewport(...).

然后用一个单位矩阵重新加载投影矩阵:

Then reload the projection matrix with an identity matrix:

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

然后:

glPerspective(...)
glMatrixMode(GL_MODELVIEW);

如果需要更改相机位置，可以在任何时候调用

gluLookAt(...).

gluLookAt(...) can be called anytime later if you need to change your camera position.

为我的简单目的而工作.

Works for my simple purposes.

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