Bug 135905
| Summary: | ios8 webgl shader compiler thinks that pow(negative_float, 2.0) is zero | ||
|---|---|---|---|
| Product: | WebKit | Reporter: | makc <makc.the.great> |
| Component: | WebGL | Assignee: | Nobody <webkit-unassigned> |
| Status: | RESOLVED WONTFIX | ||
| Severity: | Normal | CC: | ap, dino, gman, makc.the.great |
| Priority: | P2 | ||
| Version: | 528+ (Nightly build) | ||
| Hardware: | iPhone / iPad | ||
| OS: | Unspecified | ||
makc
well maybe not compiler.
Steps to Reproduce:
create any shader with x * x and pow (x, 2.0) side by side, you will see a difference.
Expected Results:
x * x is always equal to pow (x, 2.0)
Actual Results:
pow (x, 2.0) is zero when x < 0
Version:
ios 8.0 12A4345d
Configuration:
iPad 3
See this commit
https://github.com/makc/makc.github.io/commit/4221dc9788d2f509caf6427571656681fb3ad442
And the demo that is fixed by it:
http://makc.github.io/three.js/map2globe/demo.html
| Attachments | ||
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| Add attachment proposed patch, testcase, etc. |
makc
I actually have a recording of how that demo looked prior to commit: https://www.youtube.com/watch?v=y5-VwWlFZqo
Gregg Tavares
pow(x < 0, ...) is undefined behavior according to the spec
According to the OpenGL ES GLSL 1.0 spec
https://www.khronos.org/files/opengles_shading_language.pdf
Section 8.2
genType pow (genType x, genType y)
Returns x raised to the y power, i.e., x ^ y
Results are undefined if x < 0.
Results are undefined if x = 0 and y <= 0.