From 3e21a014c308a87e1dd7bdabba255aad02d3ad1b Mon Sep 17 00:00:00 2001
From: Roland Scheidegger <sroland@tungstengraphics.com>
Date: Tue, 22 May 2007 03:29:59 +0200
Subject: [PATCH] fog: fix issues with negative fog coords (may fix #10529)

Rework tnl fog a bit. Make sure we always use ABS(eyez) when fog coord source
is depth, OTOH it does not seem to be necessary to use it (as was done before
in some cases) if fog coord source is fogcoord (just to save some work).
This fixes tests/fog (the first 2 cases) with i915/i915tex.
---
 src/mesa/tnl/t_vb_fog.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/mesa/tnl/t_vb_fog.c b/src/mesa/tnl/t_vb_fog.c
index 5440ff7894d..f6518500d80 100644
--- a/src/mesa/tnl/t_vb_fog.c
+++ b/src/mesa/tnl/t_vb_fog.c
@@ -114,7 +114,7 @@ compute_fog_blend_factors(GLcontext *ctx, GLvector4f *out, const GLvector4f *in)
       else
          d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
-         const GLfloat z = FABSF(*v);
+         const GLfloat z = *v;
          GLfloat f = (end - z) * d;
 	 data[i][0] = CLAMP(f, 0.0F, 1.0F);
       }
@@ -122,14 +122,14 @@ compute_fog_blend_factors(GLcontext *ctx, GLvector4f *out, const GLvector4f *in)
    case GL_EXP:
       d = ctx->Fog.Density;
       for ( i = 0 ; i < n ; i++, STRIDE_F(v,stride)) {
-         const GLfloat z = FABSF(*v);
+         const GLfloat z = *v;
          NEG_EXP( data[i][0], d * z );
       }
       break;
    case GL_EXP2:
       d = ctx->Fog.Density*ctx->Fog.Density;
       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
-         const GLfloat z = FABSF(*v);
+         const GLfloat z = *v;
          NEG_EXP( data[i][0], d * z * z );
       }
       break;
@@ -153,6 +153,8 @@ run_fog_stage(GLcontext *ctx, struct tnl_pipeline_stage *stage)
 
 
    if (ctx->Fog.FogCoordinateSource == GL_FRAGMENT_DEPTH_EXT) {
+      GLuint i;
+      GLfloat *coord;
       /* Fog is computed from vertex or fragment Z values */
       /* source = VB->ObjPtr or VB->EyePtr coords */
       /* dest = VB->AttribPtr[_TNL_ATTRIB_FOG] = fog stage private storage */
@@ -168,6 +170,8 @@ run_fog_stage(GLcontext *ctx, struct tnl_pipeline_stage *stage)
 	 input = &store->fogcoord;
 
          /* NOTE: negate plane here so we get positive fog coords! */
+	 /* NOTE2: this doesn't always work (tests/fog - all frag depth fog
+	    coords will be negative). */
 	 plane[0] = -m[2];
 	 plane[1] = -m[6];
 	 plane[2] = -m[10];
@@ -180,18 +184,29 @@ run_fog_stage(GLcontext *ctx, struct tnl_pipeline_stage *stage)
 					      VB->ObjPtr, plane );
 
 	 input->count = VB->ObjPtr->count;
+
+	 /* make sure coords are really positive
+	    NOTE should avoid going through array twice */
+	 coord = input->start;
+	 for (i = 0; i < input->count; i++) {
+	    input->data[i][0] = FABSF(*coord);
+	    STRIDE_F(coord, input->stride);
+	 }
       }
       else {
          /* fog coordinates = eye Z coordinates (use ABS later) */
-	 input = &store->input;
+	 input = &store->fogcoord;
 
 	 if (VB->EyePtr->size < 2)
 	    _mesa_vector4f_clean_elem( VB->EyePtr, VB->Count, 2 );
 
-	 input->data = (GLfloat (*)[4]) &(VB->EyePtr->data[0][2]);
-	 input->start = VB->EyePtr->start+2;
-	 input->stride = VB->EyePtr->stride;
+	 input->stride = 4 * sizeof(GLfloat);
 	 input->count = VB->EyePtr->count;
+	 coord = VB->EyePtr->start;
+	 for (i = 0 ; i < VB->EyePtr->count; i++) {
+	    input->data[i][0] = FABSF(coord[2]);
+	    STRIDE_F(coord, VB->EyePtr->stride);
+	 }
       }
    }
    else {
-- 
2.30.2