From: Axel Davy <davyaxel0@gmail.com>
Date: Thu, 16 Aug 2018 14:29:31 +0000 (+0200)
Subject: st/nine: Use perspective correction for ps depth fog
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a9bf82ecf4c284989c40e4e6c1f6962bc9bd58d2;p=mesa.git

st/nine: Use perspective correction for ps depth fog

Emulate perspective interpolation of depth for programmable ps fog

ff ps fog uses position z, or 1/w depending on the ff
projection matrix set. This is according to public documents
found describing the algorithm and tests we made.

In the case of programmable ps, we used position's z,
which was sufficient to pass wine tests (which test shaders
don't set w).

Issue https://github.com/iXit/Mesa-3D/issues/315 showed
that this calculation was wrong.
Using perspective interpolation on z, that is using z * 1/w
seems to satisfy both this application and wine tests.

Fixes: https://github.com/iXit/Mesa-3D/issues/315

Signed-off-by: Axel Davy <davyaxel0@gmail.com>
---

diff --git a/src/gallium/state_trackers/nine/nine_shader.c b/src/gallium/state_trackers/nine/nine_shader.c
index 5b8ad3f161e..913508fb889 100644
--- a/src/gallium/state_trackers/nine/nine_shader.c
+++ b/src/gallium/state_trackers/nine/nine_shader.c
@@ -3458,8 +3458,8 @@ shader_add_ps_fog_stage(struct shader_translator *tx, struct ureg_src src_col)
     struct ureg_program *ureg = tx->ureg;
     struct ureg_dst oCol0 = ureg_DECL_output(ureg, TGSI_SEMANTIC_COLOR, 0);
     struct ureg_src fog_end, fog_coeff, fog_density;
-    struct ureg_src fog_vs, depth, fog_color;
-    struct ureg_dst fog_factor;
+    struct ureg_src fog_vs, fog_color;
+    struct ureg_dst fog_factor, depth;
 
     if (!tx->info->fog_enable) {
         ureg_MOV(ureg, oCol0, src_col);
@@ -3467,8 +3467,10 @@ shader_add_ps_fog_stage(struct shader_translator *tx, struct ureg_src src_col)
     }
 
     if (tx->info->fog_mode != D3DFOG_NONE) {
-        depth = nine_get_position_input(tx);
-        depth = ureg_scalar(depth, TGSI_SWIZZLE_Z);
+        depth = tx_scratch_scalar(tx);
+        /* Depth used for fog is perspective interpolated */
+        ureg_RCP(ureg, depth, ureg_scalar(nine_get_position_input(tx), TGSI_SWIZZLE_W));
+        ureg_MUL(ureg, depth, ureg_src(depth), ureg_scalar(nine_get_position_input(tx), TGSI_SWIZZLE_Z));
     }
 
     nine_info_mark_const_f_used(tx->info, 33);
@@ -3478,16 +3480,16 @@ shader_add_ps_fog_stage(struct shader_translator *tx, struct ureg_src src_col)
     if (tx->info->fog_mode == D3DFOG_LINEAR) {
         fog_end = NINE_CONSTANT_SRC_SWIZZLE(33, X);
         fog_coeff = NINE_CONSTANT_SRC_SWIZZLE(33, Y);
-        ureg_ADD(ureg, fog_factor, fog_end, ureg_negate(depth));
+        ureg_ADD(ureg, fog_factor, fog_end, ureg_negate(ureg_src(depth)));
         ureg_MUL(ureg, ureg_saturate(fog_factor), tx_src_scalar(fog_factor), fog_coeff);
     } else if (tx->info->fog_mode == D3DFOG_EXP) {
         fog_density = NINE_CONSTANT_SRC_SWIZZLE(33, X);
-        ureg_MUL(ureg, fog_factor, depth, fog_density);
+        ureg_MUL(ureg, fog_factor, ureg_src(depth), fog_density);
         ureg_MUL(ureg, fog_factor, tx_src_scalar(fog_factor), ureg_imm1f(ureg, -1.442695f));
         ureg_EX2(ureg, fog_factor, tx_src_scalar(fog_factor));
     } else if (tx->info->fog_mode == D3DFOG_EXP2) {
         fog_density = NINE_CONSTANT_SRC_SWIZZLE(33, X);
-        ureg_MUL(ureg, fog_factor, depth, fog_density);
+        ureg_MUL(ureg, fog_factor, ureg_src(depth), fog_density);
         ureg_MUL(ureg, fog_factor, tx_src_scalar(fog_factor), tx_src_scalar(fog_factor));
         ureg_MUL(ureg, fog_factor, tx_src_scalar(fog_factor), ureg_imm1f(ureg, -1.442695f));
         ureg_EX2(ureg, fog_factor, tx_src_scalar(fog_factor));