Fix broken map on pitch=0 on some systems #3740
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lucaswoj
reviewed
Dec 5, 2016
| @@ -408,6 +408,9 @@ class Transform { | |||
| mat4.perspective(m, 2 * Math.atan((this.height / 2) / this.altitude), this.width / this.height, 0.1, farZ); | |||
| mat4.translate(m, m, [0, 0, -this.altitude]); | |||
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| // a hack around https://github.com/mapbox/mapbox-gl-js/issues/2270 | |||
| m[14] = Math.min(m[14], m[15]); | |||
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The rewards of this not-100%-understood fix outweigh the severity of the bug & risks of the fix in my mind.
Out of curiosity, is there any intuitive meaning of elements 14 and 15 in the transformation matrix? Can we anticipate any cases where elements 14 and 15 might end up with very different values? cc @ansis
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There seem to be no intuitive meaning since the perspective projection math is a bit involved, but at this point of position matrix calculation, m[15] always equals the altitude value (1.5), and m[14] represents translation along Z axis (which always seems to be <=1.5).
lucaswoj
approved these changes
Dec 5, 2016
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Fixes #2270 by making sure a floating point error does not accumulate into a broken projection matrix.
When pitch = 0, a
Float32Arrayperspective matrix would end up with1.5000001192092896, 1.5as the last values, whileFloat64Arrayproduces correct1.5, 1.5. Empirically, I found that the first value never exceeds the second one with proper precision. When it does (which happens even withFloat64Arrayon some systems), the map disappears. So while I don't fully grasp the math behind this, this hack seems to fix the pitch=0 bug.cc @ansis @jfirebaugh @lucaswoj