Use appropriate UNPACK_ALIGNMENT for data textures #13013
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📦 Preview the examples and docs from this branch here: https://deploy-preview-13013--ol-site.netlify.app/. |
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I used a modified version of the Data Tiles examples https://codesandbox.io/s/data-tiles-forked-yx559?file=/main.js to check the calculations work - it could be used as the basis for rendering tests if needed. |
src/ol/webgl/TileTexture.js
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| @@ -84,6 +93,7 @@ function uploadDataTexture(helper, texture, data, size, bandCount) { | |||
| textureType, | |||
| data | |||
| ); | |||
| gl.pixelStorei(gl.UNPACK_ALIGNMENT, 4); | |||
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We can restore this to the previous gl.getParameter(gl.UNPACK_ALIGNMENT) value. I've changed this in the latest commit.
src/ol/webgl/TileTexture.js
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| data, | ||
| size, | ||
| bandCount, | ||
| unpackAlignment |
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Instead of adding another argument, this function can determine the optimal unpack alignment based on data.byteLength / size[1]. I've changed this in the latest commit.
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Thanks for identifying this issue and putting together a fix, @mike-000. I think it is worth describing two separate issues that your change addresses. The first issue is with texture data where the "byte width" (or number of bytes per row) is not divisible by 4. This is the issue described in #12995 (e.g. 3-band, 8-bit data and a tile width of 25). This can be addressed by setting the appropriate The second change you've made here is to allow "loosely packed" data tiles (where the band count x tile width x tile height is not the same as the length of the data array). I'm not sure when we might encounter these. But I think it makes sense to respect the provided tile width (and height) in this case. I've added rendering tests for these two separate cases and reworked the alignment handling a bit. |
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Fixes #12995
Most of the time (RGBA data and/or standard tile sizes) the default
UNPACK_ALIGNMENTvalue of 4 has no problems. However a combination of RBG or other data and non-standard tile sizes may mean this does not work. The calculations assumed anUNPACK_ALIGNMENTof 1 (not a valid assumption) but continued to use the default value, It is possible to avoid assumptions and calculate an appropriate value from the datasizeandbyteLengthand set that when uploading data textures, then restore the default value. It should not be necessary for the application to guess a value and patch it in the prerender event.