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st/mesa: change SQRT lowering to fix the game Risen

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Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94627
(against nouveau)

Acked-by: Ilia Mirkin <imirkin@alum.mit.edu>
This commit is contained in:
Marek Olšák 2016-05-30 17:43:26 +02:00
parent 991cbfcb14
commit 589d6b58c3
1 changed files with 9 additions and 7 deletions
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16
src/mesa/state_tracker/st_glsl_to_tgsi.cpp
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@ -1901,13 +1901,15 @@ glsl_to_tgsi_visitor::visit_expression(ir_expression* ir, st_src_reg *op)
if (have_sqrt) {
emit_scalar(ir, TGSI_OPCODE_SQRT, result_dst, op[0]);
} else {
/* sqrt(x) = x * rsq(x). */
emit_scalar(ir, TGSI_OPCODE_RSQ, result_dst, op[0]);
emit_asm(ir, TGSI_OPCODE_MUL, result_dst, result_src, op[0]);
/* For incoming channels <= 0, set the result to 0. */
op[0].negate = ~op[0].negate;
emit_asm(ir, TGSI_OPCODE_CMP, result_dst,
op[0], result_src, st_src_reg_for_float(0.0));
/* This is the only instruction sequence that makes the game "Risen"
* render correctly. ABS is not required for the game, but since GLSL
* declares negative values as "undefined", allowing us to do whatever
* we want, I choose to use ABS to match DX9 and pre-GLSL RSQ
* behavior.
*/
emit_scalar(ir, TGSI_OPCODE_ABS, result_dst, op[0]);
emit_scalar(ir, TGSI_OPCODE_RSQ, result_dst, result_src);
emit_scalar(ir, TGSI_OPCODE_RCP, result_dst, result_src);
}
break;
case ir_unop_rsq: