[Mesa-dev] [PATCH 2/3] i965: Add runtime checks for line antialiasing in Gen < 6.

[Iago Toral Quiroga]

In Gen < 6 the hardware generates a runtime bit that indicates whether AA data
has to be sent as part of the framebuffer write SEND message. This affects the
specific case where we have setup antialiased line rendering and we render
polygons which have one face setup in GL_LINE mode (line antialiasing
will be used) and the other one in GL_FILL mode (no line antialiasing needed).

Currently we are not doing this runtime test and instead we always send AA
data, which produces incorrect rendering of the GL_FILL face of the polygon in
in the aforementioned scenario (verified in ironlake and gm45).

In Gen4 this is, likely, a regression introduced with commit 098acf6c843. In
Gen5 this has never worked properly. Gen > 5 are not affected by this.

The patch fixes the problem by adding the appropriate runtime check and
adjusting the framebuffer write message accordingly in the conflictive
scenario (detected with fs_visitor::runtime_check_aads_emit == TRUE).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78679
---
 src/mesa/drivers/dri/i965/brw_fs.h           |  4 ++
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 86 +++++++++++++++++-----------
 2 files changed, 58 insertions(+), 32 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 60a4906..ab8912f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -452,6 +452,10 @@ public:
 
    void emit_color_write(int target, int index, int first_color_mrf);
    void emit_alpha_test();
+   void do_emit_fb_write(int target, int base_mrf, int mlen, bool eot,
+                         bool header_present);
+   void emit_fb_write(int target, int base_mrf, int mlen, bool eot,
+                      bool header_present);
    void emit_fb_writes();
 
    void emit_shader_time_begin();
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 171f063..4c3897b 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -2731,6 +2731,54 @@ fs_visitor::emit_alpha_test()
 }
 
 void
+fs_visitor::do_emit_fb_write(int target, int base_mrf, int mlen, bool eot,
+                             bool header_present)
+{
+   fs_inst *inst = emit(FS_OPCODE_FB_WRITE);
+   inst->target = target;
+   inst->base_mrf = base_mrf;
+   inst->mlen = mlen;
+   inst->eot = eot;
+   inst->header_present = header_present;
+   if ((brw->gen >= 8 || brw->is_haswell) && fp->UsesKill) {
+      inst->predicate = BRW_PREDICATE_NORMAL;
+      inst->flag_subreg = 1;
+   }
+}
+
+void
+fs_visitor::emit_fb_write(int target, int base_mrf, int mlen, bool eot,
+                          bool header_present)
+{
+   if (!runtime_check_aads_emit) {
+      do_emit_fb_write(target, base_mrf, mlen, eot, header_present);
+   } else {
+      /* This can only happen in Gen < 6
+       */
+      fs_reg reg_tmp_ud = fs_reg(this, glsl_type::uint_type);
+      emit(AND(reg_tmp_ud,
+               fs_reg(get_element_ud(brw_vec8_grf(1,0), 6)),
+               fs_reg(brw_imm_ud(1<<26))));
+      emit(CMP(reg_null_ud,
+               reg_tmp_ud,
+               fs_reg(brw_imm_ud(0)),
+               BRW_CONDITIONAL_Z));
+      emit(IF(BRW_PREDICATE_NORMAL));
+      {
+         /* Shift message header one register since we are not sending
+          * AA data stored in base_mrf+2
+          */
+         do_emit_fb_write(target, base_mrf + 1, mlen - 1, eot, header_present);
+      }
+      emit(BRW_OPCODE_ELSE);
+      {
+         do_emit_fb_write(target, base_mrf, mlen, eot, header_present);
+      }
+      emit(BRW_OPCODE_ENDIF);
+   }
+}
+
+void
 fs_visitor::emit_fb_writes()
 {
    this->current_annotation = "FB write header";
@@ -2848,16 +2896,7 @@ fs_visitor::emit_fb_writes()
       if (INTEL_DEBUG & DEBUG_SHADER_TIME)
          emit_shader_time_end();
 
-      fs_inst *inst = emit(FS_OPCODE_FB_WRITE);
-      inst->target = 0;
-      inst->base_mrf = base_mrf;
-      inst->mlen = nr - base_mrf;
-      inst->eot = true;
-      inst->header_present = header_present;
-      if ((brw->gen >= 8 || brw->is_haswell) && fp->UsesKill) {
-         inst->predicate = BRW_PREDICATE_NORMAL;
-         inst->flag_subreg = 1;
-      }
+      emit_fb_write(0, base_mrf, nr - base_mrf, true, header_present);
 
       prog_data->dual_src_blend = true;
       this->current_annotation = NULL;
@@ -2894,19 +2933,10 @@ fs_visitor::emit_fb_writes()
             emit_shader_time_end();
       }
 
-      fs_inst *inst = emit(FS_OPCODE_FB_WRITE);
-      inst->target = target;
-      inst->base_mrf = base_mrf;
-      if (src0_alpha_to_render_target && target == 0)
-         inst->mlen = nr - base_mrf - reg_width;
-      else
-         inst->mlen = nr - base_mrf;
-      inst->eot = eot;
-      inst->header_present = header_present;
-      if ((brw->gen >= 8 || brw->is_haswell) && fp->UsesKill) {
-         inst->predicate = BRW_PREDICATE_NORMAL;
-         inst->flag_subreg = 1;
-      }
+      int mlen = (src0_alpha_to_render_target && target == 0) ?
+         nr - base_mrf - reg_width : nr - base_mrf;
+
+      emit_fb_write(target, base_mrf, mlen, eot, header_present);
    }
 
    if (key->nr_color_regions == 0) {
@@ -2919,15 +2949,7 @@ fs_visitor::emit_fb_writes()
       if (INTEL_DEBUG & DEBUG_SHADER_TIME)
          emit_shader_time_end();
 
-      fs_inst *inst = emit(FS_OPCODE_FB_WRITE);
-      inst->base_mrf = base_mrf;
-      inst->mlen = nr - base_mrf;
-      inst->eot = true;
-      inst->header_present = header_present;
-      if ((brw->gen >= 8 || brw->is_haswell) && fp->UsesKill) {
-         inst->predicate = BRW_PREDICATE_NORMAL;
-         inst->flag_subreg = 1;
-      }
+      emit_fb_write(0, base_mrf, nr - base_mrf, true, header_present);
    }
 
    this->current_annotation = NULL;
-- 
1.9.1