I have no objection to adding a note to the spec. I would prefer something along the lines of:At the absolute minimum, we need wording in the spec that spells this out: "We send decoded image data top-row-first into texImage2D, which, per spec, expects bottom-row-first data. This means that textures uploaded this way will be upside down compared to textures uploaded via other methods. You can force HTML element uploads to upload bottom-row-first by using UNPACK_FLIP_Y_WEBGL=true, but this also flips the order that TypedArray rows are uploaded."
The default texture coordinate system in OpenGL is such that the first row of data loaded by texImage2D will appear at bottom of the texture. However the first row of data in HTML elements is the logical top of the image therefore textures uploaded from HTML elements will appear upside down. One way of adjusting for this is to set UNPACK_FLIP_Y_WEBGL=true. Then texImage2D will flip the rows of data as it uploads them. UNPACK_FLIP_Y_WEBGL affects the operation of texImage2D for all data sources.
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