[Mesa-dev] [PATCH] mesa: clamp MaxLevel for immutable textures at initialization

[Fredrik Höglund]

On Thursday 22 October 2015, Nicolai Hähnle wrote:
> The same clamping already happens for glTexParameteri. This change
> also fixes a bug in mipmap generation, see
> https://bugs.freedesktop.org/show_bug.cgi?id=91993

I don't think this patch is correct.  The ARB_texture_view specification
doesn't say that MaxLevel should be initialized to the value of
TEXTURE_IMMUTABLE_LEVELS, only that it's interpreted relative to
the view and not relative to the original data store.

Liam Middlebrook also pointed out recently that the clamping done
in glTexParameteri is in fact a bug:

http://lists.freedesktop.org/archives/piglit/2015-June/016342.html

The language in the specification that says that MaxLevel is clamped
when the texture is immutable applies to texture minification,
magnification, and texture completeness; not to gl*Tex*Parameter*.

> piglit test cases have been submitted for review (as additions to
> arb_texture_storage-texture-storage and arb_texture_view-max-level).
>
> ---
>  src/mesa/main/textureview.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/src/mesa/main/textureview.c b/src/mesa/main/textureview.c
> index 04b7d73..b6eaa77 100644
> --- a/src/mesa/main/textureview.c
> +++ b/src/mesa/main/textureview.c
> @@ -408,6 +408,8 @@ _mesa_set_texture_view_state(struct gl_context *ctx,
>        texObj->NumLayers = 6;
>        break;
>     }
> +
> +   texObj->MaxLevel = MIN2(texObj->MaxLevel, texObj->ImmutableLevels - 1);
>  }
>  
>  /**
> @@ -680,6 +682,7 @@ _mesa_TextureView(GLuint texture, GLenum target, GLuint origtexture,
>     texObj->NumLayers = newViewNumLayers;
>     texObj->Immutable = GL_TRUE;
>     texObj->ImmutableLevels = origTexObj->ImmutableLevels;
> +   texObj->MaxLevel = MIN2(texObj->MaxLevel, texObj->ImmutableLevels - 1);
>     texObj->Target = target;
>     texObj->TargetIndex = _mesa_tex_target_to_index(ctx, target);
>     assert(texObj->TargetIndex < NUM_TEXTURE_TARGETS);
>