skia2/resources/sksl/shared/ConstVariableComparison.sksl
Brian Osman 7b361499c9 Align SkSL const rules more closely with GLSL
This adds Analysis::IsConstantExpression, to determine if an expression
is a constant-expression. It now expands to cover 'const' local and
global variables, because we also enforce that the initializer on those
variables is - in turn - a constant expression.

This fixes 10837 - previously you could initialize a const variable with
a non-constant expression, and we'd emit GLSL that contained that same
pattern, which would fail to compile at the driver level. That should
not be possible any longer.

Bug: skia:10679
Bug: skia:10837
Change-Id: I517820ef4da57fff45768c0b04c55aebc18d3272
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/375856
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2021-02-26 17:44:11 +00:00

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uniform half4 colorGreen, colorRed;
half4 main() {
const float4 a = float4(0);
const float4 b = float4(1);
// This is a constant-expression in GLSL, but not in SkSL (yet).
// We can't declare this const, and we can't eliminate it. skbug.com/10835
/*const*/ float4 c = abs(b);
if (a == b || b != c) {
return colorRed;
} else {
return colorGreen;
}
}