在顶点着色器中将顶点转换到球面。

I'm programming a (hopefully) planetary shader for a Unity project. I'm relatively new to shaders, and as I understand the language here is a subset of CG Shader called ShaderLab.

我正在为一个联合项目设计一个(希望)行星着色器。我对着色器比较陌生，我理解这里的语言是一个叫做ShaderLab的CG着色器的子集。

My question is can this be done in a shader? I have the formulas to map coords to a sphere, but I just get a tangled mess. I used the same formulas in an XNA project to map planes from a unit cube to a unit sphere and it worked fine. What am I doing wrong?

我的问题是，这能在着色器中完成吗?我有把坐标映射到球面的公式，但我只是得到了一个混乱的混乱。我在XNA项目中使用了相同的公式，将平面从一个单位立方体映射到一个单位球体，它运行得很好。我做错了什么?

Oh, and I'm testing this on a stock plane prefab in Unity placed at (0, 1, 0), scale (1, 1, 1).

哦，我在一个平面预置的平面上测试它(0,1,0)，标度(1,1,1)

Things to note:

注意事项:

• appdata_base : a vertex format that consists of position, normal and one texture coordinate
• appdata_base:由位置、正常和一个纹理坐标组成的顶点格式。
• _Object2World : current model matrix from Unity
• _Object2World:来自Unity的当前模型矩阵。
• UNITY_MATRIX_VP : current view * projection matrix from Unity
• UNITY_MATRIX_VP:当前视图*来自Unity的投影矩阵。

Here is my vertex shader:

这是我的顶点着色器:

struct v2f {
    float4 pos : SV_POSITION;
    float3 col : COLOR0;
};

v2f vert(appdata_base v) {
    v2f o;
    o.pos = v.vertex;
    o.pos = mul(_Object2World, o.pos); // _Object2World is the current model matrix from UNITY

    o.pos.x *= sqrt(1 - o.pos.y * o.pos.y / 2 - o.pos.z * o.pos.z / 2 + o.pos.y * o.pos.y * o.pos.z * o.pos.z / 3);
    o.pos.y *= sqrt(1 - o.pos.z * o.pos.z / 2 - o.pos.x * o.pos.x / 2 + o.pos.z * o.pos.z * o.pos.x * o.pos.x / 3);
    o.pos.z *= sqrt(1 - o.pos.x * o.pos.x / 2 - o.pos.y * o.pos.y / 2 + o.pos.x * o.pos.x * o.pos.y * o.pos.y / 3);

    o.pos = mul(UNITY_MATRIX_VP, o.pos);            
    o.col = v.normal * 0.5 + 0.5;

    return o;
}

1 个解决方案

#1

I found a silly mistake in my code. I was setting 'o.pos.x' to it's new value, then figuring the result for 'o.pos.y' using the new value I just calculated for 'o.pos.x'. The code below works satisfactorily in answering my question.

我在我的代码中发现了一个愚蠢的错误。我是设置的o.pos。x'到它的新值，然后计算结果。y'用我刚才计算的新值。下面的代码很好地回答了我的问题。

To comment further, mapping coordinates to a sphere is possible in a vertex shader in Unity. However, my end goal is impossible or much more challenging which is to map terrain coordinates onto a sphere. Unity doesn't allow terrain meshes to be rotated and seemingly imposes other restrictions. It might be possible to achieve such mapping with a more advanced vertex shader.

若要进一步评论，在一个顶点着色器中，可以将坐标映射到一个球体。然而，我的最终目标是不可能的，或者更具有挑战性的是将地形坐标映射到一个球体上。Unity不允许地形网格被旋转，并且似乎强加其他限制。可以用更高级的顶点着色器实现这样的映射。

struct v2f {
    float4 pos : SV_POSITION;
    float3 col : COLOR0;
};

v2f vert(appdata_base v) {
    v2f o;

    float4 p = v.vertex;

    p.x *= sqrt(1 - v.vertex.y * v.vertex.y / 2 - v.vertex.z * v.vertex.z / 2 + v.vertex.y * v.vertex.y * v.vertex.z * v.vertex.z / 3);
    p.y *= sqrt(1 - v.vertex.z * v.vertex.z / 2 - v.vertex.x * v.vertex.x / 2 + v.vertex.z * v.vertex.z * v.vertex.x * v.vertex.x / 3);
    p.z *= sqrt(1 - v.vertex.x * v.vertex.x / 2 - v.vertex.y * v.vertex.y / 2 + v.vertex.x * v.vertex.x * v.vertex.y * v.vertex.y / 3);

    o.pos = mul(UNITY_MATRIX_MVP, p);
    o.col = v.normal * 0.5 + 0.5;

    return o;
}