[Mesa-stable] [PATCH] glsl: Allow overlapping locations for vertex input attributes
Anuj Phogat
anuj.phogat at gmail.com
Thu Mar 13 15:39:58 PDT 2014
On Tue, Mar 11, 2014 at 10:37 AM, Ian Romanick <idr at freedesktop.org> wrote:
> On 03/10/2014 04:15 PM, Anuj Phogat wrote:
> >
> >
> >
> > On Mon, Mar 10, 2014 at 3:27 PM, Ian Romanick <idr at freedesktop.org
> > <mailto:idr at freedesktop.org>> wrote:
> >
> > On 03/10/2014 11:19 AM, Anuj Phogat wrote:
> > > Currently overlapping locations of input variables are not allowed
> > for all
> > > the shader types in OpenGL and OpenGL ES.
> > >
> > >>From OpenGL ES 3.0 spec, page 56:
> > > "Binding more than one attribute name to the same location is
> > referred
> > > to as aliasing, and is not permitted in OpenGL ES Shading
> Language
> > > 3.00 vertex shaders. LinkProgram will fail when this condition
> > exists.
> > > However, aliasing is possible in OpenGL ES Shading Language
> > 1.00 vertex
> > > shaders."
> > >
> > > Taking in to account what different versions of OpenGL and OpenGL
> > ES specs
> > > say about aliasing:
> > > - It is allowed only on vertex shader input attributes in
> > OpenGL (2.0 and
> > > above) and OpenGL ES 2.0.
> > > - It is explictly disallowed in OpenGL ES 3.0.
> > >
> > > Fixes Khronos CTS failing test:
> > > explicit_attrib_location_vertex_input_aliased.test
> > > See more details about this at below mentioned khronos bug.
> > >
> > > Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com
> > <mailto:anuj.phogat at gmail.com>>
> > > Cc: "9.2 10.0 10.1" <mesa-stable at lists.freedesktop.org
> > <mailto:mesa-stable at lists.freedesktop.org>>
> > > Bugzilla: Khronos #9609
> > > ---
> > > src/glsl/linker.cpp | 74
> > +++++++++++++++++++++++++++++++++++++++++++----------
> > > 1 file changed, 61 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
> > > index a619bc8..9bd698b 100644
> > > --- a/src/glsl/linker.cpp
> > > +++ b/src/glsl/linker.cpp
> > > @@ -1798,10 +1798,12 @@
> > assign_attribute_or_color_locations(gl_shader_program *prog,
> > > * active attribute array, both of which require
> > multiple
> > > * contiguous generic attributes."
> > > *
> > > - * Previous versions of the spec contain similar
> > language but omit
> > > - * the bit about attribute arrays.
> > > + * I think above text prohibits the aliasing of explicit
> and
> > > + * automatic assignments. But, aliasing is allowed in
> manual
> > > + * assignments of attribute locations. See below
> > comments for
> > > + * the details.
> >
> > The text above (outside the diff) forbids things like:
> >
> > layout(location=0) in mat4 m;
> > layout(location=1) in vec4 v;
> >
> > where v and m now partially overlap because m consumes 4 slots (0
> > through 3, inclusive).
> >
> >
> > This should not be a problem as along as there's only one active
> attribute
> > in vertex shader. If a developer uses such locations, its his
> > responsibility
> > to use just one of them in any path in shader program. Khronos CTS test
> > also expects linking to happen in above case.
> >
> > OpenGL 4.0 spec makes similar looking statements at two different places.
> > First for vertex shader input locations at page 60:
> >
> > "LinkProgram will fail if the attribute bindings assigned by BindAttri-
> > bLocation do not leave not enough space to assign a location for an
> > active matrix
> > attribute or an active attribute array, both of which require multiple
> > contiguous
> > generic attributes."
>
> Somewhere in the intervening specs, the language was changed. In 4.4 it
> says:
>
> "LinkProgram will fail if the attribute bindings specified either
> by BindAttribLocation or explicitly set within the shader text do
> not leave not enough space to assign a location for an active
> matrix attribute or an active attribute array, both of which
> require multiple contiguous generic attributes."
>
> > This statement sounds little unclear to me. It doesn't say what happens
> if
> > locations set in shader text don't leave enough space. It also doesn't
> make
> > clear who assigns the location in "to assign a location for an active
> > matrix".
> > explicit or automatic assignment?
>
> You may be right. We'll have to prod other implementations. I'll also
> do some spec archaeology.
>
Piglit tests I posted on mailing list passes on NVIDIA's OpenGL 4.3 linux
driver. NVIDIA allows the kind of overlapping you described above.
>
> > Second for fragment output locations at page 233:
> > "if the explicit binding assigments do not leave enough space for the
> linker
> > to automatically assign a location for a varying out array, which
> requires
> > multiple contiguous locations."
> >
> > This statement makes the condition more clear for linking error. Notice
> > the words
> > 'explicit' and 'automatically' in text from page 233.
> >
> > So I interpreted the two statements as:
> > Aliasing of explicit and automatic assignments is prohibited.
> > But, aliasing is allowed in explicit assignments of attribute locations.
> >
> > Do you interpret them differently ?
> >
> >
> > Does this patch affect this?
> >
> > Yes. It allows linking in such cases.
> >
> >
> > > *
> > > - * Page 61 of the OpenGL 4.0 spec also says:
> > > + * From OpenGL 4.0 spec, page 61:
> > > *
> > > * "It is possible for an application to bind more
> > than one
> > > * attribute name to the same location. This is
> > referred to as
> > > @@ -1814,12 +1816,48 @@
> > assign_attribute_or_color_locations(gl_shader_program *prog,
> > > * but implementations are not required to generate
> > an error
> > > * in this case."
> > > *
> > > - * These two paragraphs are either somewhat
> > contradictory, or I
> > > - * don't fully understand one or both of them.
> > > - */
> > > - /* FINISHME: The code as currently written does not
> support
> > > - * FINISHME: attribute location aliasing (see comment
> > above).
> > > + * From GLSL 4.30 spec, page 54:
> > > + *
> > > + * "A program will fail to link if any two non-vertex
> > shader
> > > + * input variables are assigned to the same
> > location. For
> > > + * vertex shaders, multiple input variables may be
> > assigned
> > > + * to the same location using either layout
> > qualifiers or via
> > > + * the OpenGL API. However, such aliasing is
> > intended only to
> > > + * support vertex shaders where each execution path
> > accesses
> > > + * at most one input per each location.
> > Implementations are
> > > + * permitted, but not required, to generate
> > link-time errors
> > > + * if they detect that every path through the vertex
> > shader
> > > + * executable accesses multiple inputs assigned to
> > any single
> > > + * location. For all shader types, a program will
> > fail to link
> > > + * if explicit location assignments leave the linker
> > unable
> > > + * to find space for other variables without explicit
> > > + * assignments."
> > > + *
> > > + * From OpenGL ES 3.0 spec, page 56:
> > > + *
> > > + * "Binding more than one attribute name to the same
> > location
> > > + * is referred to as aliasing, and is not permitted
> > in OpenGL
> > > + * ES Shading Language 3.00 vertex shaders.
> > LinkProgram will
> > > + * fail when this condition exists. However,
> aliasing is
> > > + * possible in OpenGL ES Shading Language 1.00
> > vertex shaders.
> > > + * This will only work if only one of the aliased
> > attributes
> > > + * is active in the executable program, or if no
> > path through
> > > + * the shader consumes more than one attribute of a
> > set of
> > > + * attributes aliased to the same location. A link
> > error can
> > > + * occur if the linker determines that every path
> > through the
> > > + * shader consumes multiple aliased attributes, but
> > implemen-
> > > + * tations are not required to generate an error in
> > this case."
> > > + *
> > > + * After looking at above references from OpenGL,
> > OpenGL ES
> > > + * and GLSL specifications, we allow aliasing of
> > vertex input
> > > + * variables in: OpenGL 2.0 (and above) and OpenGL
> > ES 2.0.
> > > + *
> > > + * NOTE: This is not required by the spec but its
> worth
> > > + * mentioning here that we're not doing anything to
> > make sure
> > > + * that no path through the vertex shader executable
> > accesses
> > > + * multiple inputs assigned to any single location.
> >
> > These last two paragraphis should be un-indented.
> >
> > > */
> > > +
> > > /* Mask representing the contiguous slots that will be
> > used by
> > > * this attribute.
> > > */
> > > @@ -1832,11 +1870,21 @@
> > assign_attribute_or_color_locations(gl_shader_program *prog,
> > > if ((~(use_mask << attr) & used_locations) !=
> > used_locations) {
> > > const char *const string = (target_index ==
> > MESA_SHADER_VERTEX)
> > > ? "vertex shader input" : "fragment shader output";
> > > - linker_error(prog,
> > > - "insufficient contiguous locations "
> > > - "available for %s `%s' %d %d %d", string,
> > > - var->name, used_locations, use_mask,
> attr);
> > > - return false;
> > > +
> > > + if (target_index == MESA_SHADER_FRAGMENT ||
> > > + (prog->IsES && prog->Version >= 300)) {
> > > +
> > > + linker_error(prog,
> > > + "overlapping location is assigned "
> > > + "to %s `%s' %d %d %d\n", string,
> > > + var->name, used_locations,
> > use_mask, attr);
> > > + return false;
> > > + } else {
> > > + linker_warning(prog,
> > > + "overlapping location is
> assigned "
> > > + "to %s `%s' %d %d %d\n", string,
> > > + var->name, used_locations,
> > use_mask, attr);
> > > + }
> > > }
> > >
> > > used_locations |= (use_mask << attr);
> >
> >
>
>
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