Fix broken line clipping.

When both ends of the line were clipped, we were using the new v0 instead
of the original v0 when computing the location of the second vertex. Thus,
the second vertex's position was incorrect.
Thanks to Heath Feather for finding a test case.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/mesa/tnl/t_vb_cliptmp.h b/src/mesa/tnl/t_vb_cliptmp.h
index e5e379e151..788fe329ed 100644
--- a/src/mesa/tnl/t_vb_cliptmp.h
+++ b/src/mesa/tnl/t_vb_cliptmp.h
@@ -1,6 +1,6 @@
 /*
  * Mesa 3-D graphics library
- * Version:  6.5.1
+ * Version:  6.5.2
  *
  * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
  *
@@ -125,6 +125,7 @@ TAG(clip_line)( GLcontext *ctx, GLuint v0, GLuint v1, GLubyte mask )
    GLfloat t0 = 0;
    GLfloat t1 = 0;
    GLuint p;
+   const GLuint v0_orig = v0;
 
    if (mask & 0x3f) {
       LINE_CLIP( CLIP_RIGHT_BIT,  -1,  0,  0, 1 );
@@ -157,9 +158,13 @@ TAG(clip_line)( GLcontext *ctx, GLuint v0, GLuint v1, GLubyte mask )
       ASSERT(t0 == 0.0);
    }
 
+   /* Note: we need to use vertex v0_orig when computing the new
+    * interpolated/clipped vertex position, not the current v0 which
+    * may have got set when we clipped the other end of the line!
+    */
    if (VB->ClipMask[v1]) {
-      INTERP_4F( t1, coord[newvert], coord[v1], coord[v0] );
-      interp( ctx, t1, newvert, v1, v0, GL_FALSE );
+      INTERP_4F( t1, coord[newvert], coord[v1], coord[v0_orig] );
+      interp( ctx, t1, newvert, v1, v0_orig, GL_FALSE );
 
       if (ctx->Light.ShadeModel == GL_FLAT)
 	 tnl->Driver.Render.CopyPV( ctx, newvert, v1 );