1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
|
[require]
GLSL >= 1.30
[vertex shader passthrough]
[fragment shader]
#version 130
uniform float zero = 0.0;
uniform float also_zero = 0.0;
out vec4 piglit_fragcolor;
void main()
{
/* Create a value that, if it were a number, would have to be > 0. Due to
* possible flush-to-zero semantics, pretty much anything involving
* multiplication or division can be zero. However, gt_zero + ge_zero is
* gt_zero.
*/
float not_a_number = 1.0 + abs(zero / also_zero);
/* Result of the max() should be 0.0, but range analysis might incorrectly
* think that it's some value > 0.
*
* A clever optimizer will convert this to
*
* piglit_fragcolor = vec4(float(saturate(X) > 0),
* float(!(saturate(X) > 0)),
* 0, 1);
*
* Since saturate(X) must be a number, it may further convert it to
*
* piglit_fragcolor = vec4(float(saturate(X) > 0),
* float(saturate(X) <= 0),
* 0, 1);
*
* At this point, all conversions are safe and exact.
*
* There are two possible incorrect reductions here. First, range anaysis
* may detect that X must be greater than zero, so saturate(X) must also
* be greater than zero. This first comparison a tautology and the second
* comparison a contradiction. If X is NaN (as we have cleverly
* constructed here), saturate(X) should be zero instead.
*
* Second, since the calculations are not marked precise, an overzealous
* optimizer may reduce this to
*
* piglit_fragcolor = vec4(float(X > 0),
* float(X <= 0),
* 0, 1);
*
* Dropping saturate() from the greater-than comparison is safe because
* (0 > 0) is equivalent to (NaN > 0). If X is NaN, the other condition
* will also evaluate false. The GLSL spec gives quite a bit of leeway
* with respect to NaN, but that seems too far. The shader author asked
* for a result of red or green. A result of black is still "undefined
* behavior," but it's also a little mean.
*
* A result of red likely indicates the first problem, and a result of
* black likely indicates the second problem.
*/
if (min(max(not_a_number, 0.0), 1.0) > 0.0) {
piglit_fragcolor = vec4(1.0, 0.0, 0.0, 1.0);
} else {
piglit_fragcolor = vec4(0.0, 1.0, 0.0, 1.0);
}
}
[test]
draw rect -1 -1 2 2
probe all rgba 0.0 1.0 0.0 1.0
|
