[Mesa-dev] [PATCH 1/2] i965/gen9: Annotate input coverage mask change

[Ben Widawsky]

As far as I can tell, the behavior is preserved from the previous generations.
Before we set a single bit to tell the FS whether or not we'll be using an input
coverage mask. Now we have some options which are implementing various
extensions. These bits are used for the various conservative rasterization
mechanisms (for collision detection, binning, and whatever else).

I believe that the behavior is preserved because the problem which conservative
rasterization is attempting to fix would go away with the "NORMAL" mode (at the
cost of performance, I believe).

This patch serves as documentation of the change by creating the enums, as well
as giving some of the history with the links here so that the next person who
comes along and looks at it doesn't spend as long as I had to in order to
determine if there is an issue or not.

Previously, this algorithm had been done in software, and this can still be used
as long as we don't export an extension stating otherwise.

References: https://developer.nvidia.com/sites/default/files/akamai/opengl/specs/GL_NV_conservative_raster.txt
References: https://http.developer.nvidia.com/GPUGems2/gpugems2_chapter42.html
Cc: Kristian Høgsberg <krh at bitplanet.net>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/brw_defines.h   | 16 ++++++++++++++++
 src/mesa/drivers/dri/i965/gen8_ps_state.c |  8 ++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index cb5c82a..a9c1e08 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -2265,6 +2265,21 @@ enum brw_pixel_shader_computed_depth_mode {
    BRW_PSCDEPTH_ON_LE = 3, /* PS guarantees output depth <= source depth */
 };
 
+enum brw_pixel_shader_coverage_mask_mode {
+   BRW_PSICMS_OFF     = 0, /* PS does not use input coverage masks. */
+   BRW_PSICMS_NORMAL  = 1, /* Input Coverage masks based on outer conservatism
+                            * and factors in SAMPLE_MASK.  If Pixel is
+                            * conservatively covered, all samples are enabled.
+                            */
+
+   BRW_PSICMS_INNER   = 2, /* Input Coverage masks based on inner conservatism
+                            * and factors in SAMPLE_MASK.  If Pixel is
+                            * conservatively *FULLY* covered, all samples are
+                            * enabled.
+                            */
+   BRW_PCICMS_DEPTH   = 3,
+};
+
 #define _3DSTATE_PS_EXTRA                       0x784F /* GEN8+ */
 /* DW1 */
 # define GEN8_PSX_PIXEL_SHADER_VALID                    (1 << 31)
@@ -2282,6 +2297,7 @@ enum brw_pixel_shader_computed_depth_mode {
 # define GEN9_PSX_SHADER_PULLS_BARY                     (1 << 3)
 # define GEN8_PSX_SHADER_HAS_UAV                        (1 << 2)
 # define GEN8_PSX_SHADER_USES_INPUT_COVERAGE_MASK       (1 << 1)
+# define GEN9_PSX_SHADER_NORMAL_COVERAGE_MASK_SHIFT     0
 
 enum brw_wm_barycentric_interp_mode {
    BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC		= 0,
diff --git a/src/mesa/drivers/dri/i965/gen8_ps_state.c b/src/mesa/drivers/dri/i965/gen8_ps_state.c
index ae18f0f..a686fed 100644
--- a/src/mesa/drivers/dri/i965/gen8_ps_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_ps_state.c
@@ -52,8 +52,12 @@ gen8_upload_ps_extra(struct brw_context *brw,
        _mesa_get_min_invocations_per_fragment(ctx, fp, false) > 1)
       dw1 |= GEN8_PSX_SHADER_IS_PER_SAMPLE;
 
-   if (fp->Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_MASK_IN)
-      dw1 |= GEN8_PSX_SHADER_USES_INPUT_COVERAGE_MASK;
+   if (fp->Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_MASK_IN) {
+      if (brw->gen >= 9)
+         dw1 |= BRW_PSICMS_INNER << GEN9_PSX_SHADER_NORMAL_COVERAGE_MASK_SHIFT;
+      else
+         dw1 |= GEN8_PSX_SHADER_USES_INPUT_COVERAGE_MASK;
+   }
 
    if (prog_data->uses_omask)
       dw1 |= GEN8_PSX_OMASK_TO_RENDER_TARGET;
-- 
2.5.0