Mesa (master): i965/msaa: Fix centroid interpolation of unlit pixels.
Paul Berry
stereotype441 at kemper.freedesktop.org
Mon Jul 2 20:29:31 UTC 2012
Module: Mesa
Branch: master
Commit: 8313f44409ceb733e9f8835926364164237b3111
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=8313f44409ceb733e9f8835926364164237b3111
Author: Paul Berry <stereotype441 at gmail.com>
Date: Thu Jun 21 11:21:22 2012 -0700
i965/msaa: Fix centroid interpolation of unlit pixels.
>From the Ivy Bridge PRM, Vol 2 Part 1 p280-281 (3DSTATE_WM:
Barycentric Interpolation Mode):
"Errata: When Centroid Barycentric mode is required, HW may
produce incorrect interpolation results when a 2X2 pixels have
unlit pixels."
To work around this problem, after doing centroid interpolation, we
replace the centroid-interpolated values for unlit pixels with
non-centroid-interpolated values (which are interpolated at pixel
centers). This produces correct rendering at the expense of a slight
increase in shader execution time.
I've conditioned the workaround with a runtime flag
(brw->needs_unlit_centroid_workaround) in the hopes that we won't need
it in future chip generations.
Fixes piglit tests "EXT_framebuffer_multisample/interpolation {2,4}
{centroid-deriv,centroid-deriv-disabled}". All MSAA interpolation
tests pass now.
Reviewed-by: Eric Anholt <eric at anholt.net>
---
src/mesa/drivers/dri/i965/brw_context.c | 4 ++++
src/mesa/drivers/dri/i965/brw_context.h | 9 +++++++++
src/mesa/drivers/dri/i965/brw_fs.cpp | 12 ++++++++++++
src/mesa/drivers/dri/i965/brw_wm.c | 18 ++++++++++++++----
4 files changed, 39 insertions(+), 4 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index 6fb7dd2..8f53ff7 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -296,6 +296,10 @@ brwCreateContext(int api,
brw->has_negative_rhw_bug = true;
}
+ if (intel->gen <= 7) {
+ brw->needs_unlit_centroid_workaround = true;
+ }
+
brw->prim_restart.in_progress = false;
brw->prim_restart.enable_cut_index = false;
diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index 8d519e7..c1f2314 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -725,6 +725,15 @@ struct brw_context
bool has_pln;
bool precompile;
+ /**
+ * Some versions of Gen hardware don't do centroid interpolation correctly
+ * on unlit pixels, causing incorrect values for derivatives near triangle
+ * edges. Enabling this flag causes the fragment shader to use
+ * non-centroid interpolation for unlit pixels, at the expense of two extra
+ * fragment shader instructions.
+ */
+ bool needs_unlit_centroid_workaround;
+
struct {
struct brw_state_flags dirty;
} state;
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 6cef08a..3445805 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -506,6 +506,18 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
struct brw_reg interp = interp_reg(location, k);
emit_linterp(attr, fs_reg(interp), interpolation_mode,
ir->centroid);
+ if (brw->needs_unlit_centroid_workaround && ir->centroid) {
+ /* Get the pixel/sample mask into f0 so that we know
+ * which pixels are lit. Then, for each channel that is
+ * unlit, replace the centroid data with non-centroid
+ * data.
+ */
+ emit(FS_OPCODE_MOV_DISPATCH_TO_FLAGS, attr);
+ fs_inst *inst = emit_linterp(attr, fs_reg(interp),
+ interpolation_mode, false);
+ inst->predicated = true;
+ inst->predicate_inverse = true;
+ }
if (intel->gen < 6) {
emit(BRW_OPCODE_MUL, attr, attr, this->pixel_w);
}
diff --git a/src/mesa/drivers/dri/i965/brw_wm.c b/src/mesa/drivers/dri/i965/brw_wm.c
index 4a7225c..ae6c6bf 100644
--- a/src/mesa/drivers/dri/i965/brw_wm.c
+++ b/src/mesa/drivers/dri/i965/brw_wm.c
@@ -130,7 +130,8 @@ brw_wm_non_glsl_emit(struct brw_context *brw, struct brw_wm_compile *c)
* (see enum brw_wm_barycentric_interp_mode) is needed by the fragment shader.
*/
static unsigned
-brw_compute_barycentric_interp_modes(bool shade_model_flat,
+brw_compute_barycentric_interp_modes(struct brw_context *brw,
+ bool shade_model_flat,
const struct gl_fragment_program *fprog)
{
unsigned barycentric_interp_modes = 0;
@@ -154,11 +155,18 @@ brw_compute_barycentric_interp_modes(bool shade_model_flat,
if (attr == FRAG_ATTRIB_WPOS || attr == FRAG_ATTRIB_FACE)
continue;
+ /* Determine the set (or sets) of barycentric coordinates needed to
+ * interpolate this variable. Note that when
+ * brw->needs_unlit_centroid_workaround is set, centroid interpolation
+ * uses PIXEL interpolation for unlit pixels and CENTROID interpolation
+ * for lit pixels, so we need both sets of barycentric coordinates.
+ */
if (interp_qualifier == INTERP_QUALIFIER_NOPERSPECTIVE) {
if (is_centroid) {
barycentric_interp_modes |=
1 << BRW_WM_NONPERSPECTIVE_CENTROID_BARYCENTRIC;
- } else {
+ }
+ if (!is_centroid || brw->needs_unlit_centroid_workaround) {
barycentric_interp_modes |=
1 << BRW_WM_NONPERSPECTIVE_PIXEL_BARYCENTRIC;
}
@@ -168,7 +176,8 @@ brw_compute_barycentric_interp_modes(bool shade_model_flat,
if (is_centroid) {
barycentric_interp_modes |=
1 << BRW_WM_PERSPECTIVE_CENTROID_BARYCENTRIC;
- } else {
+ }
+ if (!is_centroid || brw->needs_unlit_centroid_workaround) {
barycentric_interp_modes |=
1 << BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC;
}
@@ -289,7 +298,8 @@ bool do_wm_prog(struct brw_context *brw,
brw_init_compile(brw, &c->func, c);
c->prog_data.barycentric_interp_modes =
- brw_compute_barycentric_interp_modes(c->key.flat_shade, &fp->program);
+ brw_compute_barycentric_interp_modes(brw, c->key.flat_shade,
+ &fp->program);
if (prog && prog->_LinkedShaders[MESA_SHADER_FRAGMENT]) {
if (!brw_wm_fs_emit(brw, c, prog))
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