问题描述
在GL ES 2.0函数中， texture2DLod 在片段着色器中不可用.我需要移植GLSL着色器.
In GL ES 2.0 Functions texture2DLod not available in the fragment Shader.I need to port the GLSL Shader.
在GL ES 2.0中，我只能使用 texture2D (sampler2D采样器，vec2坐标，浮点偏差)
In GL ES 2.0 I can only use texture2D(sampler2D sampler, vec2 coord, float bias)
告诉我如何计算与已知值 LOD (详细程度)等效的 bias 的值?
Tell me how to calculate the value of a bias equivalent to a known value LOD (level of detail)?
//Example GLSL:
float lod=u_lod;
textureLod(sampler, (uInverseViewMatrix * vec4(r, 0.0)).xy, lod);
//I need GL ES 2.0:
float lod=u_lod;
float bias=? <-----calc bias from lod
texture2D(sampler,(uInverseViewMatrix * vec4(r, 0.0)).xy,bias)
推荐答案
想要的东西是不可能的.
What you want is not possible.
LOD偏差恰好是: bias .它被添加到从texture2D自动计算的LOD中.
The LOD bias is exactly that: a bias. It is added to the LOD that is automatically computed from texture2D.
textureLOD不能那样工作.它选择一个特定的 LOD，该LOD不基于任何人自动计算的任何内容.
textureLOD doesn't work that way. It selects a specific LOD, which is not based on anything automatically computed by anyone.
执行所需操作的唯一方法是自己执行自动LOD计算，然后尝试计算该值与实际所需的LOD之间的偏差，然后使用texture2D对其进行应用.我将告诉您如何执行此操作，但这需要功能dFdx和dFdy，这在OpenGL ES 2.0中不是 .所以你不能.
The only way to do what you want would be to perform the automatic LOD computations yourself, then try to compute a bias between that value and the LOD you actually want, and then apply that with texture2D. I would tell you how to do that, but that would require the functions dFdx and dFdy, which are not in OpenGL ES 2.0. So you can't.
但是不要感到难过，因为即使可以，它也不起作用.另一个问题是，LOD偏置被钳制在特定范围内.注意，您不会在ES 2.0规范中找到它，但是没关系.您也不会找到关于该偏见如何应用到为mipmapping计算的lambda的任何语言.对真的;继续搜索.最接近的是GLSL ES规范，但是OpenGL ES规范并没有说明对lambda施加偏见.
But don't feel bad, because even if you could, it wouldn't work. The other problem there is that the LOD bias is clamped within a specific range. Note that you won't find this in the ES 2.0 spec, but that's OK; you also won't find any language about how that bias gets applied to the lambda computed for mipmapping. Yes, really; go ahead and search for it. The closest you get is in the GLSL ES spec, but the OpenGL ES spec says nothing about applying a bias to the lambda.
是的，这是不可能的.
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