在xz平面上绘制场景opengl [英] Drawing a scene in xz plane opengl

问题描述

我正在开发一个opengl程序。查看参数是：
eye 0 -4 6
viewup 0 1 0
lookat 0 0 0

背景矩形（具有纹理），使得我将能够从当前眼睛位置看到它。现在，眼睛从-ve Y方向看。我想要能够绘制一个覆盖整个屏幕的矩形。我不知道什么坐标给矩形和如何获得纹理映射。
目前我有这个在我的方法：
什么是同样的代码。我有这个功能：

  glPushMatrix 
 glLoadIdentity（）; 
 glBegin（GL_QUADS）; 
 glColor3f（1.0f，0.0f，0.0f）; 
 glVertex2f（-1.0，-1.0）; 
 glVertex2f（-1.0，1.0）; 
 glVertex2f（1.0，1.0）; 
 glVertex2f（1.0，-1.0）; 
 glEnd（）; 
 glPopMatrix（）; 
  

解决方案

绘制独立的背景图片的相机是在标准化设备坐标（NDC）中绘制它，并且不对其执行任何变换/投影。
要覆盖整个屏幕，你必须绘制一个从p = [-1，-1]到[1,1]的四边形。然后可以通过tex =（p + 1）/ 2找到纹理坐标。

标准化的设备坐标是在应用投影和透视除法之后通常得到的坐标。它们跨越从[-1，-1，-1]到[1,1,1]的立方体，其中近平面被映射到z = -1（至少在OpenGL中，在DirectX中，近平面被映射到z = 0）。在你的特殊情况下，深度并不重要，只要你绘制背景平面作为每个帧中的第一个元素，并禁用深度测试。

I am working on an opengl program. The viewing parameters are : eye 0 -4 6 viewup 0 1 0 lookat 0 0 0

I want to draw a background rectangle (with texture) such that I will be able to see it from the current eye location. Right now, the eye is looking from the -ve Y direction. I want to be able to draw a rectangle that covers the entire screen. I am not understanding what coordinates to give to the rectangle and how to get the texture mapping. Currently I have this in my method: What would be the code for the same. I have this in function:

glPushMatrix();
glLoadIdentity();
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(-1.0, -1.0);
glVertex2f(-1.0, 1.0);
glVertex2f(1.0, 1.0);
glVertex2f(1.0, -1.0);
glEnd();
glPopMatrix();

解决方案

The easiest option for drawing a background image that is independent of the camera is to draw it in normalized device coordinates (NDC) and do not perform any transformations/projections on it. To cover the whole screen, you have to draw a quad going from p = [-1, -1] to [1,1]. The texture coordinates can then be found by tex = (p + 1)/2

Normalized device coordinates are the coordinates one would normally get after applying projection and the perspective divide. They span a cube from [-1,-1,-1] to [1,1,1] where the near plane is mapped to z = -1 (at least in OpenGL, in DirectX the near plane is mapped to z=0). In your special case, the depth should not matter, as long as you draw the background plane as the first element in each frame and disable the depth-test.

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