Mesa (mesa_7_7_branch): softpipe: fix bug in perspective corrected interpolants for lines

[Brian Paul]

Module: Mesa
Branch: mesa_7_7_branch
Commit: 3ca6cb3440705ffec470beb601cdc0c22089e3f1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3ca6cb3440705ffec470beb601cdc0c22089e3f1

Author: Brian Paul <brianp at vmware.com>
Date:   Fri Feb  5 12:48:37 2010 -0700

softpipe: fix bug in perspective corrected interpolants for lines

Thanks to Michal for finding this.

This will get fixed on the gallium-cylindrical-wrap branch and
then merged to master.

---

 src/gallium/drivers/softpipe/sp_setup.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/src/gallium/drivers/softpipe/sp_setup.c b/src/gallium/drivers/softpipe/sp_setup.c
index 478d8ef..4cd11dd 100644
--- a/src/gallium/drivers/softpipe/sp_setup.c
+++ b/src/gallium/drivers/softpipe/sp_setup.c
@@ -805,7 +805,6 @@ line_persp_coeff(const struct setup_context *setup,
                  struct tgsi_interp_coef *coef,
                  uint vertSlot, uint i)
 {
-   /* XXX double-check/verify this arithmetic */
    const float a0 = setup->vmin[vertSlot][i] * setup->vmin[0][3];
    const float a1 = setup->vmax[vertSlot][i] * setup->vmax[0][3];
    const float da = a1 - a0;
@@ -813,7 +812,7 @@ line_persp_coeff(const struct setup_context *setup,
    const float dady = da * setup->emaj.dy * setup->oneoverarea;
    coef->dadx[i] = dadx;
    coef->dady[i] = dady;
-   coef->a0[i] = (setup->vmin[vertSlot][i] -
+   coef->a0[i] = (a0 -
                   (dadx * (setup->vmin[0][0] - setup->pixel_offset) +
                    dady * (setup->vmin[0][1] - setup->pixel_offset)));
 }