[Mesa-dev] [PATCH 04/13] nouveau: Fix non-1x post-scale factor with DOT3 combiner

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

Fixes long standing bug on NV10 and NV20 where using a non-1x RGB or A
post-scale with GL_DOT3_RGB or GL_DOT3_RGBA texture environment would
not work.

The old combiner math uses HALF_BIAS_NORMAL and HALF_BIAS_NEGATE.  The
GL_NV_register_combiners defines these as

    HALF_BIAS_NORMAL_NV       max(0.0, e) - 0.5
    HALF_BIAS_NEGATE_NV       -max(0.0, e) + 0.5

In order to get the correct result from the dot-product, the
intermediate dot-product must be multiplied by 4.  This is a literal
implementation of the GL_ARB_texture_env_dot3 spec.  It also requires
using the register combiner post-scale.  As a result, the post-scale
cannot be used for the post-scale set by the application.

The new combiner math uses EXPAND_NORMAL and EXPAND_NEGATE.  The
GL_NV_register_combiners defines these as

    EXPAND_NORMAL_NV          2.0 * max(0.0, e) - 1.0
    EXPAND_NEGATE_NV          -2.0 * max(0.0, e) + 1.0

Since this fully expands the value to [-1, 1] range, the intermediate
dot-product result is the desired value.  This leaves the register
combiner post-scale available for application use.

NOTE: I have not actually tested this.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/mesa/drivers/dri/nouveau/nv10_state_frag.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/mesa/drivers/dri/nouveau/nv10_state_frag.c b/src/mesa/drivers/dri/nouveau/nv10_state_frag.c
index c007c6c..e78eac3 100644
--- a/src/mesa/drivers/dri/nouveau/nv10_state_frag.c
+++ b/src/mesa/drivers/dri/nouveau/nv10_state_frag.c
@@ -135,7 +135,7 @@ get_input_source(struct combiner_state *rc, int source)
 /* Get the RC input mapping for the specified texture_env_combine
  * operand, possibly inverted or biased. */
 #define INVERT 0x1
-#define HALF_BIAS 0x2
+#define NORMALIZE 0x2
 
 static uint32_t
 get_input_mapping(struct combiner_state *rc, int operand, int flags)
@@ -148,12 +148,12 @@ get_input_mapping(struct combiner_state *rc, int operand, int flags)
 		map |= RC_IN_USAGE(ALPHA);
 
 	if (is_negative_operand(operand) == !(flags & INVERT))
-		map |= flags & HALF_BIAS ?
-			RC_IN_MAPPING(HALF_BIAS_NEGATE) :
+		map |= flags & NORMALIZE ?
+			RC_IN_MAPPING(EXPAND_NEGATE) :
 			RC_IN_MAPPING(UNSIGNED_INVERT);
 	else
-		map |= flags & HALF_BIAS ?
-			RC_IN_MAPPING(HALF_BIAS_NORMAL) :
+		map |= flags & NORMALIZE ?
+			RC_IN_MAPPING(EXPAND_NORMAL) :
 			RC_IN_MAPPING(UNSIGNED_IDENTITY);
 
 	return map;
@@ -270,12 +270,10 @@ setup_combiner(struct combiner_state *rc)
 
 	case GL_DOT3_RGB:
 	case GL_DOT3_RGBA:
-		INPUT_ARG(rc, A, 0, HALF_BIAS);
-		INPUT_ARG(rc, B, 1, HALF_BIAS);
+		INPUT_ARG(rc, A, 0, NORMALIZE);
+		INPUT_ARG(rc, B, 1, NORMALIZE);
 
-		rc->out = RC_OUT_DOT_AB | RC_OUT_SCALE_4;
-
-		assert(!rc->logscale);
+		rc->out = RC_OUT_DOT_AB;
 		break;
 
 	default:
-- 
2.5.5