r300/compiler: make shadow sampler codegen more readable, add comments

diff --git a/src/mesa/drivers/dri/r300/compiler/radeon_program_tex.c b/src/mesa/drivers/dri/r300/compiler/radeon_program_tex.c
index 98e391a..e1bb7c7 100644 (file)
--- a/src/mesa/drivers/dri/r300/compiler/radeon_program_tex.c
+++ b/src/mesa/drivers/dri/r300/compiler/radeon_program_tex.c
@@ -116,45 +116,53 @@ int radeonTransformTEX(
                        struct rc_instruction * inst_rcp = rc_insert_new_instruction(c, inst);
                        struct rc_instruction * inst_mad = rc_insert_new_instruction(c, inst_rcp);
                        struct rc_instruction * inst_cmp = rc_insert_new_instruction(c, inst_mad);
+                       unsigned tmp_recip_w = rc_find_free_temporary(c);
+                       unsigned tmp_texsample = rc_find_free_temporary(c);
+                       unsigned tmp_sum = rc_find_free_temporary(c);
                        int pass, fail;
 
+                       /* Save the output register. */
+                       struct rc_dst_register output_reg = inst->U.I.DstReg;
+
+                       /* Redirect TEX to a new temp. */
+                       inst->U.I.DstReg.File = RC_FILE_TEMPORARY;
+                       inst->U.I.DstReg.Index = tmp_texsample;
+                       inst->U.I.DstReg.WriteMask = RC_MASK_XYZW;
+
+                       /* Compute 1/W. */
                        inst_rcp->U.I.Opcode = RC_OPCODE_RCP;
                        inst_rcp->U.I.DstReg.File = RC_FILE_TEMPORARY;
-                       inst_rcp->U.I.DstReg.Index = rc_find_free_temporary(c);
+                       inst_rcp->U.I.DstReg.Index = tmp_recip_w;
                        inst_rcp->U.I.DstReg.WriteMask = RC_MASK_W;
                        inst_rcp->U.I.SrcReg[0] = inst->U.I.SrcReg[0];
                        inst_rcp->U.I.SrcReg[0].Swizzle = RC_SWIZZLE_WWWW;
 
-                       inst_cmp->U.I.DstReg = inst->U.I.DstReg;
-                       inst->U.I.DstReg.File = RC_FILE_TEMPORARY;
-                       inst->U.I.DstReg.Index = rc_find_free_temporary(c);
-                       inst->U.I.DstReg.WriteMask = RC_MASK_XYZW;
-
+                       /* Perspective-divide r (=depth) by W and add the texture sample (see below). */
                        inst_mad->U.I.Opcode = RC_OPCODE_MAD;
                        inst_mad->U.I.DstReg.File = RC_FILE_TEMPORARY;
-                       inst_mad->U.I.DstReg.Index = rc_find_free_temporary(c);
+                       inst_mad->U.I.DstReg.Index = tmp_sum;
                        inst_mad->U.I.SrcReg[0] = inst->U.I.SrcReg[0];
                        inst_mad->U.I.SrcReg[0].Swizzle = RC_SWIZZLE_ZZZZ;
                        inst_mad->U.I.SrcReg[1].File = RC_FILE_TEMPORARY;
-                       inst_mad->U.I.SrcReg[1].Index = inst_rcp->U.I.DstReg.Index;
+                       inst_mad->U.I.SrcReg[1].Index = tmp_recip_w;
                        inst_mad->U.I.SrcReg[1].Swizzle = RC_SWIZZLE_WWWW;
                        inst_mad->U.I.SrcReg[2].File = RC_FILE_TEMPORARY;
-                       inst_mad->U.I.SrcReg[2].Index = inst->U.I.DstReg.Index;
+                       inst_mad->U.I.SrcReg[2].Index = tmp_texsample;
                        inst_mad->U.I.SrcReg[2].Swizzle = compiler->state.unit[inst->U.I.TexSrcUnit].depth_texture_swizzle;
 
                        /* Recall that SrcReg[0] is tex, SrcReg[2] is r and:
-                        *   r  < tex  <=>      -tex+r < 0
-                        *   r >= tex  <=> not (-tex+r < 0 */
+                        *   LESS:    r  < tex  <=>      -tex+r < 0
+                        *   GEQUAL:  r >= tex  <=> not (-tex+r < 0)
+                        *   GREATER: r  > tex  <=>       tex-r < 0
+                        *   LEQUAL:  r <= tex  <=> not ( tex-r < 0)
+                        *
+                        * This negates either r or tex: */
                        if (comparefunc == RC_COMPARE_FUNC_LESS || comparefunc == RC_COMPARE_FUNC_GEQUAL)
                                inst_mad->U.I.SrcReg[2].Negate = inst_mad->U.I.SrcReg[2].Negate ^ RC_MASK_XYZW;
                        else
                                inst_mad->U.I.SrcReg[0].Negate = inst_mad->U.I.SrcReg[0].Negate ^ RC_MASK_XYZW;
 
-                       inst_cmp->U.I.Opcode = RC_OPCODE_CMP;
-                       /* DstReg has been filled out above */
-                       inst_cmp->U.I.SrcReg[0].File = RC_FILE_TEMPORARY;
-                       inst_cmp->U.I.SrcReg[0].Index = inst_mad->U.I.DstReg.Index;
-
+                       /* This negates the whole expresion: */
                        if (comparefunc == RC_COMPARE_FUNC_LESS || comparefunc == RC_COMPARE_FUNC_GREATER) {
                                pass = 1;
                                fail = 2;
@@ -163,6 +171,10 @@ int radeonTransformTEX(
                                fail = 1;
                        }
 
+                       inst_cmp->U.I.Opcode = RC_OPCODE_CMP;
+                       inst_cmp->U.I.DstReg = output_reg;
+                       inst_cmp->U.I.SrcReg[0].File = RC_FILE_TEMPORARY;
+                       inst_cmp->U.I.SrcReg[0].Index = tmp_sum;
                        inst_cmp->U.I.SrcReg[pass].File = RC_FILE_NONE;
                        inst_cmp->U.I.SrcReg[pass].Swizzle = RC_SWIZZLE_1111;
                        inst_cmp->U.I.SrcReg[fail] = shadow_ambient(compiler, inst->U.I.TexSrcUnit);