从屏幕坐标计算光线方向矢量 [英] Calculate ray direction vector from screen coordanate

问题描述

我正在寻找一种更好的方法（或者说，这是是最好的方式）将像素坐标从任意相机传输到相应的光线方向位置/方向。

I'm looking for a better way (or a note that this is the best way) to transfer a pixel coordinate to its corresponding ray direction from a arbitrary camera position/direction.

我当前的方法如下。我定义一个摄像机作为位置矢量，外观矢量和向上矢量，命名为。 （注意，观察向量是相机所面向的方向上的单位向量，NOT（（position-lookat）是方向，XNA的Matrix.CreateLookAt中的标准）这三个向量可以唯一地定义相机位置。这里是实际的代码（好吧，不是真的，简单的抽象版本）（语言是HLSL）

My current method is as follows. I define a "camera" as a position vector, lookat vector, and up vector, named as such. (Note that the lookat vector is a unit vector in the direction the camera is facing, NOT where (position - lookat) is the direction, as is the standard in XNA's Matrix.CreateLookAt) These three vectors can uniquely define a camera position. Here's the actual code (well, not really the actual, a simplified abstracted version) (Language is HLSL)

float xPixelCoordShifted = (xPixelCoord / screenWidth * 2 - 1) * aspectRatio;
float yPixelCoordShifted = yPixelCoord / screenHeight * 2 - 1;
float3 right = cross(lookat, up);
float3 actualUp = cross(right, lookat);
float3 rightShift = mul(right, xPixelCoordShifted);
float3 upShift = mul(actualUp, yPixelCoordShifted);
return normalize(lookat + rightShift + upShift);

（返回值是光线的方向）

(the return value is the direction of the ray)

所以我要问的是，这是一个更好的方法来做到这一点，也许使用矩阵等。这个方法的问题是，如果你有太宽的视角，屏幕的边缘

So what I'm asking is this- What's a better way to do this, maybe using matrices, etc. The problem with this method is that if you have too wide a viewing angle, the edges of the screen get sort of "radially stretched".

推荐答案

您可以计算它（ ray ）in像素着色器，HLSL代码：

You can calculate it (ray) in pixel shader, HLSL code:

float4x4 WorldViewProjMatrix; // World*View*Proj
float4x4 WorldViewProjMatrixInv; // (World*View*Proj)^(-1)

void VS( float4 vPos : POSITION,
     out float4 oPos : POSITION,
     out float4 pos  : TEXCOORD0 )
{
    oPos = mul(vPos, WorldViewProjMatrix);
    pos = oPos;
}

float4 PS( float4 pos : TEXCOORD0 )
{
    float4 posWS = mul(pos, WorldViewProjMatrixInv);
    float3 ray = posWS.xyz / posWS.w;

    return float4(0, 0, 0, 1);
}

相机的位置和方向信息位于 View matrix（Matrix.CreateLookAt）。

The information about your camera's position and direction is in View matrix (Matrix.CreateLookAt).

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