[PATCH] st/mesa: fix WPOS adjustment

[Christoph Bumiller]

For the first change, where we want to convert from half integer
to integer coordinates, consider the upper left position:

u,h -> l,i /  0.5 -> 99.0 : ( 0.5 - 0.5) * -1 + 99
u,h -> u,i /  0.5 ->  0.0 : ( 0.5 - 0.5)
l,h -> u,i / 99.5 ->  0.0 : (99.5 - 0.5) * -1 + 99
l,h -> l,i / 99.5 -> 99.0 : (99.5 - 0.5)
---
 src/mesa/state_tracker/st_mesa_to_tgsi.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/src/mesa/state_tracker/st_mesa_to_tgsi.c b/src/mesa/state_tracker/st_mesa_to_tgsi.c
index c07739f..6a63a39 100644
--- a/src/mesa/state_tracker/st_mesa_to_tgsi.c
+++ b/src/mesa/state_tracker/st_mesa_to_tgsi.c
@@ -883,7 +883,7 @@ emit_wpos(struct st_context *st,
          ureg_property_fs_coord_pixel_center(ureg, TGSI_FS_COORD_PIXEL_CENTER_INTEGER);
       else if (pscreen->get_param(pscreen, PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_HALF_INTEGER))
          /* the driver supports pixel center half integer, need to bias X,Y */
-         emit_adjusted_wpos(t, program, 0.5f, invert ? 0.5f : -0.5f);
+         emit_adjusted_wpos(t, program, -0.5f, -0.5f);
       else
          assert(0);
    }
@@ -891,6 +891,10 @@ emit_wpos(struct st_context *st,
       /* Fragment shader wants pixel center half integer */
       if (pscreen->get_param(pscreen, PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_HALF_INTEGER)) {
          /* the driver supports pixel center half integer */
+         if (invert) {
+            /* for h = 100: (0.5 -> 99.5) by ((0.5 - 1.0) * -1 + 99.0) */
+            emit_adjusted_wpos(t, program, 0.0f, -1.0f);
+         }
       }
       else if (pscreen->get_param(pscreen, PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_INTEGER)) {
          /* the driver supports pixel center integer, need to bias X,Y */
-- 
1.7.3.4


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