Bug 135905

Summary: ios8 webgl shader compiler thinks that pow(negative_float, 2.0) is zero
Product: WebKit Reporter: makc <makc.the.great>
Component: WebGLAssignee: Nobody <webkit-unassigned>
Severity: Normal CC: ap, dino, gman, makc.the.great
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: iPhone / iPad   
OS: Unspecified   

Description makc 2014-08-13 14:35:07 PDT
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

ios 8.0 12A4345d

iPad 3

See this commit

And the demo that is fixed by it:
Comment 1 makc 2014-08-13 14:38:25 PDT
I actually have a recording of how that demo looked prior to commit: https://www.youtube.com/watch?v=y5-VwWlFZqo
Comment 2 Gregg Tavares 2019-07-22 21:42:06 PDT
pow(x < 0, ...) is undefined behavior according to the spec

According to the OpenGL ES GLSL 1.0 spec


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.