From b39e6f33b60ef9bbaf81f320aaca6a440d8a6a8f Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Wed, 22 Sep 2010 11:47:03 -0700
Subject: glsl: Rework assignments with write_masks to have LHS chan count
match RHS.
It turns out that most people new to this IR are surprised when an
assignment to (say) 3 components on the LHS takes 4 components on the
RHS. It also makes for quite strange IR output:
(assign (constant bool (1)) (x) (var_ref color) (swiz x (var_ref v) ))
(assign (constant bool (1)) (y) (var_ref color) (swiz yy (var_ref v) ))
(assign (constant bool (1)) (z) (var_ref color) (swiz zzz (var_ref v) ))
But even worse, even we get it wrong, as shown by this line of our
current step(float, vec4):
(assign (constant bool (1)) (w)
(var_ref t)
(expression float b2f (expression bool >=
(swiz w (var_ref x))(var_ref edge))))
where we try to assign a float to the writemasked-out x channel and
don't supply anything for the actual w channel we're writing. Drivers
right now just get lucky since ir_to_mesa spams the float value across
all the source channels of a vec4.
Instead, the RHS will now have a number of components equal to the
number of components actually being written. Hopefully this confuses
everyone less, and it also makes codegen for a scalar target simpler.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
---
src/mesa/program/ir_to_mesa.cpp | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
(limited to 'src/mesa/program')
diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index f24dce79f6..de0cb1ac5b 100644
--- a/src/mesa/program/ir_to_mesa.cpp
+++ b/src/mesa/program/ir_to_mesa.cpp
@@ -1577,13 +1577,39 @@ ir_to_mesa_visitor::visit(ir_assignment *ir)
assert(!ir->lhs->type->is_scalar() && !ir->lhs->type->is_vector());
l.writemask = WRITEMASK_XYZW;
} else if (ir->lhs->type->is_scalar()) {
- /* FINISHME: This hack makes writing to gl_FragData, which lives in the
+ /* FINISHME: This hack makes writing to gl_FragDepth, which lives in the
* FINISHME: W component of fragment shader output zero, work correctly.
*/
l.writemask = WRITEMASK_XYZW;
} else {
+ int swizzles[4];
+ int first_enabled_chan = 0;
+ int rhs_chan = 0;
+
assert(ir->lhs->type->is_vector());
l.writemask = ir->write_mask;
+
+ for (int i = 0; i < 4; i++) {
+ if (l.writemask & (1 << i)) {
+ first_enabled_chan = GET_SWZ(r.swizzle, i);
+ break;
+ }
+ }
+
+ /* Swizzle a small RHS vector into the channels being written.
+ *
+ * glsl ir treats write_mask as dictating how many channels are
+ * present on the RHS while Mesa IR treats write_mask as just
+ * showing which channels of the vec4 RHS get written.
+ */
+ for (int i = 0; i < 4; i++) {
+ if (l.writemask & (1 << i))
+ swizzles[i] = GET_SWZ(r.swizzle, rhs_chan++);
+ else
+ swizzles[i] = first_enabled_chan;
+ }
+ r.swizzle = MAKE_SWIZZLE4(swizzles[0], swizzles[1],
+ swizzles[2], swizzles[3]);
}
assert(l.file != PROGRAM_UNDEFINED);
--
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