1 files changed, 24 insertions, 2 deletions
diff --git a/src/mesa/main/stencil.c b/src/mesa/main/stencil.c
index b4ea9978d87..15c98e20156 100644
--- a/src/mesa/main/stencil.c
+++ b/src/mesa/main/stencil.c
@@ -27,6 +27,23 @@
  * \file stencil.c
  * Stencil operations.
  *
+ * Note: There's some conflict between GL_EXT_stencil_two_side and
+ * OpenGL 2.0's two-sided stencil feature.
+ *
+ * With GL_EXT_stencil_two_side, calling glStencilOp/Func/Mask() only the
+ * front OR back face state (as set by glActiveStencilFaceEXT) is set.
+ *
+ * But with OpenGL 2.0, calling glStencilOp/Func/Mask() sets BOTH the
+ * front AND back state.
+ *
+ * Also, note that GL_ATI_separate_stencil is different as well:
+ * glStencilFuncSeparateATI(GLenum frontfunc, GLenum backfunc, ...)  vs.
+ * glStencilFuncSeparate(GLenum face, GLenum func, ...).
+ *
+ * This problem is solved by keeping three sets of stencil state:
+ *  state[0] = GL_FRONT state.
+ *  state[1] = OpenGL 2.0 / GL_ATI_separate_stencil GL_BACK state.
+ *  state[2] = GL_EXT_stencil_two_side GL_BACK state.
  */
 
 
@@ -519,7 +536,11 @@ _mesa_update_stencil(GLcontext *ctx)
 {
    const GLint face = ctx->Stencil._BackFace;
 
-   ctx->Stencil._TestTwoSide =
+   ctx->Stencil._Enabled = (ctx->Stencil.Enabled &&
+                            ctx->DrawBuffer->Visual.stencilBits > 0);
+
+    ctx->Stencil._TestTwoSide =
+       ctx->Stencil._Enabled &&
        (ctx->Stencil.Function[0] != ctx->Stencil.Function[face] ||
 	ctx->Stencil.FailFunc[0] != ctx->Stencil.FailFunc[face] ||
 	ctx->Stencil.ZPassFunc[0] != ctx->Stencil.ZPassFunc[face] ||
@@ -542,7 +563,7 @@ _mesa_init_stencil(GLcontext *ctx)
 {
    ctx->Stencil.Enabled = GL_FALSE;
    ctx->Stencil.TestTwoSide = GL_FALSE;
-   ctx->Stencil.ActiveFace = 0;  /* 0 = GL_FRONT, 1 = GL_BACK */
+   ctx->Stencil.ActiveFace = 0;  /* 0 = GL_FRONT, 2 = GL_BACK */
    ctx->Stencil.Function[0] = GL_ALWAYS;
    ctx->Stencil.Function[1] = GL_ALWAYS;
    ctx->Stencil.Function[2] = GL_ALWAYS;
@@ -565,4 +586,5 @@ _mesa_init_stencil(GLcontext *ctx)
    ctx->Stencil.WriteMask[1] = ~0U;
    ctx->Stencil.WriteMask[2] = ~0U;
    ctx->Stencil.Clear = 0;
+   ctx->Stencil._BackFace = 1;
 }