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CubeTexture: Clarify envMap flip. #20490

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Oct 10, 2020
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CubeTexture: Clarify envMap flip. #20490

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10 changes: 10 additions & 0 deletions src/textures/CubeTexture.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,16 @@ function CubeTexture( images, mapping, wrapS, wrapT, magFilter, minFilter, forma

this.flipY = false;

// Why CubeTexture._needsFlipEnvMap is necessary:
//
// By convention -- likely based on the RenderMan spec from the 1990's -- cube maps are specified by WebGL (and three.js)
// in a coordinate system in which positive-x is to the right when looking up the positive-z axis -- in other words,
// in a left-handed coordinate system. By continuing this convention, preexisting cube maps continued to render correctly.

// three.js uses a right-handed coordinate system. So environment maps used in three.js appear to have px and nx swapped
// and the flag _needsFlipEnvMap controls this conversion. The flip is not required (and thus _needsFlipEnvMap is set to false)
// when using WebGLCubeRenderTarget.texture as a cube texture.

this._needsFlipEnvMap = true;

}
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